Solar insolation models at Quetta v and proposal for installation of heating and cooling systems in Science Faculty V f.. *4 I , # 'ÿÿ'7 i i '/

BEING A THESIS PRESENTED

BY

AYATULLAH DURRANI

1

TO THE •N.

UNIVERSITY OF BALOCHISTAN &3v % i."- / QUETTA

IN APPLICATION FOR

rTHE DEGREE OF DOCTOR OF PHILOSOPHY

1994.

-.4 i

' -J i-j if

Dedloated to my father l*• (Late) Mouiana Mohammad Umar >• \

v CONTENTS Page No.

CHAPTER:!

1. INTRODUCTION

1.1 (A) Introduction: Solar Insolation Models.

1.2 Solar Energy Potential. )

1.3 Solar Energy Conversion. X 1.3.1 Solar Energy: Direct Conversion. X 1.3.2 Solar Energy: Indirect Conversion. 3

1.4 Solar Spectrum. 3 l.S. The sun and Solar Constant. t 1.5. 1 Sun-Earth Astronomical Relationship. k

1.5.2 Solar Declination. 7-

1.6 Characteristics and Atmospheric Attenuation 8 of Solar Radiation.

1.6.1 Extraterrestrial, Global, Diorct and Diffuse Solar 9 Radiation on Horizontal Surface.

1.7 Solar Radiation Striking on the Earth's Surface. lo

1.1.(B) Applications on Heating/Cooling Syustems.

1.2 Solar Heating/Cooling System. II 1.2.1 Collectors. 13 1.2.2 Storage Devices. 13 1.2.3 Distribution System. 1.2.4 Auxiliary Heating & Cooling. 15" 1.3. Passive System. /5*

1.4. Active System. 19

1.5 Solar Houses. 2Z-

1.6. Solar Total Energy Concept. 2.2 1.7. Cooling System Design. 57 1.8. Sun Space / Building Relationship. 7/ CHAPTER-II (A)

2.1 Results and Discussions.

2.2 Characteristics Distribution of Global Radiation at Quetta.

2.3 Sky Condition at Quetta. Aÿ- 2.4. Difluse Solar Radiation Estimation Horizontal & Inclined /££ Surface at Quetta.

2.5 Monthly Average Diffuse Solar Radiation on a Horizontal Surface.

2.6 Monthly Average Difluse Solar Radiation on Inclined A? Surface.

2.7 Direct and Diffiis Radition: Monthly Variation. l?D

2.8 Relatinship between Monthly Average Daily Diffuse and ffj Monthly Average Daily Total Radiation.

2.9 Annual Variation of the Monthly Mean Global Solar J72. Radiation.

2.10 Monthly Average Hourly Global & Diffuse Solar Radiation at Quetta. az

2.11 Estimated and Observed Hourly Global Solar 175- Radiation Data for Quetta. 2.12 Measured Average Hourly Global Solar Radiation ns Data.

2.13 Estimation of Monthly Average Diffuse Radiation from Clearness Index.

2.14 Estimation of Monthly Average Diffuse Solar Radiation Jfg from Sunshine Hours. 2.15 Calculation from Monthly Average Hourly Data. m 2.16 Calculation from Monthly Average Daily Data. 18! 2.17 Method of Calculations. 182 2.18 On the Choice of Proper Inclimation and Orientation t8£ at Comparative Study of the Azimuth angles.

2.19 Correlation of Average Diffuse Beam and Global Solar Radiation with Hours of Bright sunshine.

2.20 Optimum Tilt angle and Orientation for Solar Collection in Quetta. 189 II - (B .) Solar Heating/Cooling Systems for Buildings. /?$ 2.21 Passive Solar, Low, Energy Residences with Transparent Insulation.

2.22 Thermal Performance of the TI construction. 2x>/

2.23 Annual Collectible Energy of a Two-Axis Tracking Flat-Plate Solar Collector. -21>4

CHAPTER-111 Conclusions and Suggestions for Future Work. a// 3.1 Conclusions. 2-H 3.2 Suggestions for future work. 2/9 CERTIFICATE

It is a pleasure to certify that this is the bonafide work of Mr.Ayat-ullah Durrani.In my opinion the thesis is suitable for the consideration Ph.D. degree in physics.

( DR.SYEDÿIOHSIN"RAZA") / Research Supervisor and Chairman Department of Physics University of Balochistan Quetta. Acknowledgement

It is pleasure to record my profound indebtedness to my supervisor Professor Dr.Sycd Molisin Raza for liis constanÿcouragemcm, guidance and constructive criticism in the course of this work. I am also grateful to Dr.Naeem Farooqui for his continuous and keen interest in the progress of the research. 1 am also thankful to S,M.Nasir for his cooperation and support during research. I express my deep appreciation and gratitude to Mr.Abdul Rauf and Mr.Mohammad Salman Nazir for typing thesis so expertly and quickly. Abstract

Solar insolation models have been extensively reviewed for Quetta, Pakistan. The correlations a/ suggestÿ by Klein are found suitable for global solar radiations at Quetta and that Quetta on an average receives 763 Jo|les/nf/sec. Estimation of monthly daily diffuse radiation although found

quite reliable needs further investigations. We found reliable estimates for both global solar and

diffused solar radiations using sunshine hours. The 60 tilt surface of flat plate collector facing south

receives about 1.7 to 2.0 times the maximum irradiation on a surface with a tilt equal to latitude at

Quetta, especially in summer, whereas maximum solar energy round the year is received for the same

tilt angle. The other tilt angles of a flat plate collector are also found suitable to intercept both global

and in particular, maximum diffuse solar radiations provided declination angles and solar trackings are

adjusted.

For thermal performance of building designs, the use of transparent insulation (Tl) at Quetta

particularly in a LEGIS south facade is recommended. Qur analysis on the use of a two-axis tracking

flat plate collector is found in agreement with estimates of solar radiations. We suggested

architectural design of buildings and residences at Quetta from view point of using both active and

passive solar heating/cooling systems and with environmental and climatic considerations.

We recommend installations of prototype solar heating and cooling systems for experimental

Verification of our estimated values of solar radiations and that the monitoring of their operational

modes is as essential as architectural designing of buildings itself. Duirnel variations of solar

radiations have a significant affect as heat transfer and thermal performance of building designs. CHAPTER-I (A)

1.1. Introduction.

The economic stability and prosperity of a country

depends upon its energy consumption per capita.

It has been estimated that the world population will approximately become 6000 million by 2000 causing about

6% increase in energy demand. So the conservative and existing energy sources would not meet the requirement.

Further the developing and underdeveloped countries still do not enjoy a proper share in the consumption of energy sources. As such alternate energy sources are to be introduced to be introduced to meet the demand as prevailing resources are getting meagre in quantity and socio-economic setup would be badly effected. 1.2 Solar Bnergy Potential It has been observed that solar energy is the only dependable energy in coming years. It has following characteristics i.e., most powerful, clean, safe and inexhaustible. Historically the utilization of solar energy started in 1845 with the invention of solar boiler by

C.Gunter and later in 1876 by John Ericsson who invented several types of hot air engines (Sayigh 1977) , but the pace of research in solar energy was not fast upto first-half of the present century as of existing cheap sources of energy.

However, due to energy crises not the research in solar.

I energy has got a great momentum in industrialized countries

like USA, UK, France, Russia (USSR) , Australia and Japan, while some work is also in process in Asia, Africa, South- east Asia. Statistically it is seen that solar energy falling on earth surface is 583.3 W/m2d_1 . Further, considering the land surface only the solar energy reaching is I63.2xl012 Kwh per day with eight hours sunshine which on large scale comes out to the 30xl013 Kwh per year i.e. 60 times the world energy requirement by 2000 (Sayigh 1977) . 1.3. Solar Energy Conversion. This exhaustible energy could be used either directly

or indirectly. By direct process the solar energy is

converted into electricity while for indirect case it is converted into heat energy. 1.3.1 Direct Conversion. Using photovoltaic cell the solar energy is

directly converted into electricity. These cells can generate electricity on large scale which can be utilized over large land on individual building. In some cases dual purpose is seen i.e. producing heat and electricity.

The efficiency of simple photovoltaic cell is 35% out of which 20% is obtained. The photovoltaic system has been used in solar pump for supply of drinking water supply and irrigation in rural areas. It is also used in

Radio-bacous, community radio, TV sets, railway signal system, weather monitoring, battery charging etc.

To improve the quality of these cells,

2 considerable research has been done and technology being improved with cost reduced.

1.3.2 Indirect Conversion:

The working of solar thermal device depends on harnessing process whose basic principle in the "Greenhouse effect" described as:

Glass has the specific property of being transparent to incoming short-wave solar radiation after passing through it, strikes a material and is re-radiated as long wave length radiation. The glass then becomes opaque to this long-wavelength radiation, so heat is trapped in at {Bruce Anderson 1977) . To stop the escape of this heat from base and side walls proper insulation is being done. A cover used is made of plastic and polymets, and the absorber plate is of copper, aluminum, steel or any material painted black. The glass cover plate help to reduce the loss of heat from front while insulation reduces losses from back portion.

Now from the absorber plate, heat is transferred by conduction to a transfer fluid or some times air which flows by the help of pump or blower. This fluid or air also acts as heat exchanger.

1.4 Solar Spectrum:

The electromagnetic spectrum consists of T-rays, x-rays, uv-radiations, light, heat, radio waves and radar waves. However, the thermal radiation emitted is common known as heat and light which could be detected by human body. It is observed that most of the solar radiations lies

3 in thermal range with wave length from 0.2 to lOOOjim.

The range of invisible spectrum and division of un-spectrum is given in tabular form below:

Visible Spectrum:

Violet O.390 0.455 jim .

Blue 0.455 0.492 jim.

Green 0.492 0.577 jim.

Yellow 0.577 0.597 jim.

Orange 0.597 0.622 Lim.

Red 0.622 0 . 770 |im.

UV-Spectrum.

near uv 0.3 0.4 jim.

far uv 0.2 0.3 jim.

max uv 0.001 0.2 jim . The infra-red position of thermal radiation has following classification:

near I.R. 0 . 77 25 jim.

far I.R. 25 1000 jim.

The thermal radiation is also subdivided into short and long waves, the major contribution of solar radiation is within short wave length, also about 95% of the sun's energy lies with 0.3 jim to 2.4 jim wavelength. 1.5 The Sun and Solar Constant. The structure and characteristics of sun gives the nature of its radiations. The range of wavelength of interest is from 0.3 to 3.0 jim where 95% of its energy is found. The diameter

4 of sun is 1.39x10® Km and is 1.59x10® Km away from the earth. Its structure is divided into; solar interior,

photosphere and solar atmosphere.

The solar interior is the main mass of the sun

where gaseous pressure is of billion atmosphere, i.e., 80 to

100 times that of water. The presence of continuous energy

is due to the reason of cyclic fusion reactions.lt is

estimated that 90% of the energy generated in the region 0

to 0.23 R (R is the radius of the sun) contain 40% of the

sun's mass. The energy of this region is radiated to a

distance of 0 . 7R from the center where temperature drops to 130.000K and density to 0.07 gms/cm . Outside this zone is fluid. The upper layer of this zone is called "photosphere" which is the source of heat and light with opaque

appearance. Above this photosphere there is a transparent

layer of rarefied gas 10,000 Km thick, known as

"chromosphere" due to its red colour.Its density decreases

from 10 gm/cm at high altitudes , its luminosity fades at

6000-7000 km above the photosphere;its temperature is 4500K at base and 10 km at an elevation of 12000 km where

isothermal corona starts. The light emitted by the chromosphere is of short wavelength due to high temperature and is weak due to rarefication of gases. It contributes 10% to the total energy emitted by the sun. Finally there is corona, a whitish glowing layer which could be seen during total solar eclipse made of highly ionized gases of very low density with temperature 10® k. These factors show that sun does not in fact function as a black body radiator, at a fixed temperature.

Mathematically; the solar constant I is the energy from the sun, per unit area, per unit time, received on a unit area

of surface perpendicular to the radiation in space, at the earth's mean distance from the sun. The solar constant has

been studied in detail both on ground-base observations and

at the top of the atmosphere. The value of this constant varies from 1338 to 1368 W/m. The various values of solar constant have been compiled by Thekaekara (1973) showing

that ground base measurements are higher than high altitude measurements. The NASA value of solar constant is 1353 W/m (based on the international Pyrelaliometer scale IPC 1956) . However, a comparison on this scale value was carried out in 1970 and 1975 by WMO to establish a solar constant

Reference scale (SCRS) after re-examinations of twelve

measurements taken from air-craft, high altitudes, balloons,

satellites and rockets. Consequently the WMO has adopted a

new scale called the World Radiometrical Reference ( WRR) as a common base for all meteorological measurements. Frohlich and Collegues (1981a. 1981b) recommended 1367 W/m as solar constant value after thorough study of values from 1969 to 1980.

1.5.1 Sun-Earth Astronomical Relationship.

The earth is closest to sun on 3rd January and

farthest on 4th July, while on 4th April and 5th October,

the earth is at its mean distance from the sun.

6 Further, the earth revolves round the sun in elliptical orbit with sun at one of the foci, and the amount of solar radiation reaching the earth is inversely proportional to the square of its distance from the sun.

The mean sun-earth distance is 0.983 AU, where

1 Au is 1.496x10°8 km.

1.5.2 Solar Declination.

There is daily change in the angle between a line joining the centers of the sun and the earth to the equatorial plane. This angle is called the solar declination, A. Its value is zero at vernal and autumnal equnoues, and has a value of +23 *S°at summer solstice and

-23 for winter solstice.

Due to the fixed direction of rotation of the earth in space a different tilt or declination A of the aims relative to the sun earth line for different seasons of the year results. The earth is tilted away from the sun, in the winter in northern hemisphere and after six months, it is tilted towards the sun. The time of maximum and minimum declination are known as summer and winter solstice respectively, while in between these two seasons, the declination A through zero at vernal and autumnal equinoues. The relatives to obtain A are: A Sin (0.4 Sin (360/365 (d0 - 82))) in degrees ...(1) obtained by Perrin de Brichanbant (1975) and also A = 23.45 Sin (360/365 (dn + 285) in degrees ...(2)

7 by Cooper (1969), where dn is the day of the year. 1.6 Characteristic and Atmospheric Attenuation of

Solar Radiation.

The solar radiation falling on earths atmosphere propitious through the atmosphere the 99% of which is contained within a distance of 30 km. These radiation are absorbed and scattered by the atmospheric material . The spectral distribution to solar radiation is given as:

JÿdA,=

The spectral distribution curve for solar radiation lies below value for the reason that absorption of the solar radiation by ozone, oxygen, carlondioxide and water vapors at various wavelengths. The ozone, 03 between 10 to 40 Km from earth's surface strongly absorb uv-radiation having h = 0.20 to 0.29 jim and relatively strong between

0.29 to 0.34 fim, so no solar radiation having wavelength less than 0.3 nm biological system on earth is protected naturally by UV- radiations . The 02 absorption occurs in a very narrow line centered at = 0.76 urn, while due water vapors the absorption is visible between 0.70 to 2.2 4m. The C02 and water vapors strongly absorb thermal radiations with wavelengths larger than 2.2 urn. As a result the wavelength of the solar radiations

9 reaching earth is between 0.29 to 2.5 um and total energy under clear atmosphere is 956 W/m . There is also scattering of solar radiations by air molecules, water droplets contained in the clouds and aerosols or dust particles. The air molecules produce short wavelength scattering of solar radiations as compared to the size of the molecules so called Rayleigh Scattering, while water droplets, aerosols and other atmospheric turbidities scatter radiation in wavelengths comparable to the diameter of such particles.

1.6.1 Extra terrestrial, Global, Direct and Diffuse Solar Radiation on Horizontal Surface. The extra terrestrial radiations are outside the atmosphere depending on many solar parameters for specific location given as: HQ = 24/n Isc {1+0.033 cos (360n/365) } (cos$ cos& Sin ws + 2nwg /360 siiufr sin&) . . . (4) Where I is solar constant, n the day of the year, 6 the declination and WB being the sunrise hour angle. The variation in extraterrestrial radiation flux is also caused by earth sun distance by ± 30%. However, the part of radiation neither absorbed nor scattered comes from solar disc reaches as beam called Direct Solar Radiation or beam radiation. The scattered part of the radiation reaching earth's surface from all directions over the sky is called

4 Diffuse Solar Radiation.

Thus the Global Solar Radiation H received by the

earth's surface is composed of direct, and diffuse

components. The diffuse component varies from 10% of the

total on a clear day to 100% on cloudy day. Clouds being one

of the major contributor of diffuse radiation determine the

transmission through the atmosphere as well.

1.7 Solar Radiation Striking on the Barth's Surface.

The amount of solar energy reaching the earth's

surface depends on the orientation of the surface with

respect to the sun, the hour of the day, the day of the year

and the latitude of the point of observation and the

atmospheric conditions. The

solar radiations follow oblique path in early morning or

late afternoon producing greater atmospheric attenuation and

laser intensity.

The total energy flux received per unit area of a

surface at the ground level is composed of direct and diffuse components. If qdf is diffuse solar radiation in W/m2 incident on horizontal surface and qD the direct radiation flux per unit area normal to the direct of the

solar beam on the ground level and 8 the angle of incidence so total flux qt received per unit area is given as: { qt = qD cosG + qdf } W/m2 - . . (5)

So, to calculate the Global (total) solar

radiation the diffuse, direct radiation flux must be known.

/0 Chapter-I (B)

Introduction .

1. Solar Heatinq/Coolincr:

The heating of residences by the use of solar radiation is a very ancient concept, and it has been used since man first began to build habitations as indicated by

John I. Yellott. One of the outstanding examples of natural solar heating is the

Indian cliff dwelling known as "Montezuma's Castle, "located some 80 miles north of Phoenix, Arizona. During the winter, the sun shines directly upon the south-facing surface of this remarkable "apartment house, " heating the masonry, and, because of the time lag imposed by he thick walls, providing heat to the structure at night. During the day, the residual heat in the walls and the additional heat that enter through the relatively small windows was apparently enough to produce comfortable conditions. During the summer, natural ventilation was adequate.

There was very little apparent activity in the field of solar heating until the beginning of interest in the utilization of solar energy for many different purposes which occurred about a century ago. One outstanding example was the use by Professor E.S. Morse, of Salem,

Massachusetts, in 1881, of "a surface of blackened slate under glass, fixed to the sunny side of a house with vents in the walls, so arranged that the cold air of a room is let

// out at the bottom of the slate and forced in again at the top by the ascending heated column between the slate and the glass.

The first scientific work on solar heating began in

1940, at Massachusetts Institute of Technology, Cambridge

Massachusetts, when a team of engineers, under the direction of Dr. Hoyt Hottel. The first definitive paper on flat plate collectors for this service was published by Dr. Hottel in

1942, and other papers followed to lay a solid foundation for the analytical study of the type of collector which is most widely used in solar heating and cooling of residences. Whillier and Hottel (1955) . There are two primary categories into which virtually all solar heating systems may be divided. The first is passive systems, in which solar radiation is collected by some element of the structure itself, or admitted directly into the building through large, south-facing windows. The second is the active systems, which generally consist of (a) separate solar collectors, which may heat either water or air, (b) storage devices which can accumulate the collected energy for use at night and during inclement days, and (c) a backup system to provide heat for protracted periods of bad weather. Heat is transferred from the collectors or from the storage means by conventional equipment such as fan-coil units, when hot or cold water is provided: fans, ducts, and air outlets when the heat transfer medium is air: and radiant means when heating is the only task which must be accomplished.

a /..?•/. Collectors: In active solar heating systems, a separate

collector is generally used, and this may be built into the structure as a part of the roof or a south-facing wall, or it may be a separate device. A wide variety of solar

collectors has been developed over the years, starting with

the simplest version, which is simply a zigzag pattern of

cooper tubes soldered to a flat copper plate, and proceeding

through many other variation to the most recent development, which uses the Roll-Bond" process. Many versions of

galvanized steel collectors have been made. Yellott (1974)

shows 14 different varieties of solar water and air heaters.

Collection efficiency is dependent upon the transmittance of

the cover glass, the absorbtance for solar radiation of the

absorber plate, and the longwave omittance of the plate,

varies with the time of day, and is dependent upon the

number of hours away from solar noon, for south-facing

collectors.

/.j.2> Storage Devices:

The storage of heat or cold is an essential part of

a complete solar heating and cooling system, since there is

no solar energy available at night, and, in virtually every

location throughout the world, there will come a time when

there will be three or more almost sunless days in succession. The types of heat storage systems are few in

number, consisting primarily of tanks full of water, some times with an antifreeze liquid additive, or containers

13 filled with small rocks. The rock bed system is used with

air as the heat transfer medium, and this combination has

the advantage that it cannot freeze and leaks are generally not serious. The water system has the advantage of being

able to store far more heat in a given volume and weight.

Water is another heat-of -fusion material which, when it

freezes at 0 C (32 F) , gives up its latent heat of fusion, 335KJ/kg (144Btu/lb) . When it melts, the same amount of heat must be added to it. This procedure has been used for many

years in the dairy industry to enable a relatively small refrigeration system to cool a large amount of milk in a

short period of time by the melting of ice which has been

stored up during off-peak periods.

A23 > Distribution Systems: When water is used as the heat transport medium,

the heat is carried into the structure by means of supply

and return pipes, and the air within the structure is heated by blowing it over a finned coil, using a fan-coil

combination of the type widely used in the heating and air

conditioning industry. Radiant heating may also be used,

employing either thin tubes along the upper portions of a wall, just below the ceiling, or using tubes embedded within

ceilings or floors. When air is the heat transport medium,

the fan which draws the air through the collector and blows

it into the storage may be used also to cause the air to

flow to the various rooms which are being heated. When

cooling is attempted, the fan-coil system is the most widely used type, since it can both heat and cool, depending upon

the temperature of the water flowing though its tubes. 1.2*4- Auxiliary Heating and Cooling: An auxiliary heater or cooler is one which is

called upon the carry part of the load during periods of

highest heating or cooling demand. It may be a fuel-burning

heater, an electric heater, or a compression refrigeration system operating as a heat pump in the heating mode. For

cooling, the heat pump offers a very good solution to the problem, since it can both cool in the summer and heat in

the winter. /•3. Passive Systems: An increasing number of residences using various

passive have been built. Fig. (1) shows the very unusual house.

•«» « *> I I

L"-W»». -J

l ie. /. The Baer house near Albuquerque, using vviilcr barrel* mounted horizontally behind insulating panels which Can be lowered during the day lime lo admit tolar radiation. and raised again at night lo conserve the collected solar radiation.

This consists of four interconnected dome-type segments,

called zomes. The south-facing wall of each of these element is gazed with single glass, and behind the blazing is a water-wall, consisting of 20 to 25 steel drums, with their

exposed ends painted black to absorb the incoming solar

radiation. The indoor surfaces of the barrels are painted in various colors, since black is not needed for longwave radiation, and the drums provide heat to the interior of the structure primarily by radiant transfer. In front of these south walls are flat panels of insulating materials, hinged at their lower edges, and provided with a simple means by which they can be lowered with the sun begins to strike them, and raised again at night or during bad weather .Domestic hot water is supplied by a battery of four flat plate collectors on the east side of the house, and a windmill supplies a modest amount of electricity, so that the house can become at least partially self-sustaining. Fig. (2) shows another residence uses a conventional

r" w\ WrFfi Y i

FIG. ji.' Paul Davis residence in Albuquerque, with uir healers providing hoi air in charge, hy ihermmyphon action, rock bed storage enclosed bcneaili paiio. The house is Manned ai nighl by hem stored in the rock bed, and a fireplace provides the necessary auxiliary heat. Cooling in summer is adequately provided by ventilation through open windows. air heater and a rock bed storage bin located beneath the patio on the side of the house. Solar heating is accomplished partially by allowing direct radiation to enter through the windows, and these are provided with insulating shutters on the inside so that, somewhat like the head wall they can be blocked off at night to prevent excessive heat loss. The unique feature of this house is the fact that it

/6 uses thermosyphon action to cause circulation of warm air upward to the collector during the sunlit hours of the day.

The air then passes into the top of the rock bed, and moves slowly downward through the rock, giving up the absorbed heat to the storage system. The cooled air recenters the collector, and this action continues throughout the day. At night, the warm air back from the house to the bottom of the rock bed . One of the most original developments in solar heating and natural cooling is the Skytherm system, invented by Horold Hay. The structure features at steel panel ceiling-roof which supports ponds of water enclosed within plastic bags. The water is in thermal contact with the roof- ceiling, and the house is heated by radiation from the roof to the floor and walls. It is cooled in summer by radiation from the floor and walls and the occupants to the ceiling which transmits the absorbed heat to the water. The system operates, because it has thermal valve in the form of insulating panels that can roll horizontally to cover the water ponds during winter nights and summer day. The solar radiation is absorbed by a black lining beneath the water ponds, and this in turn heats both the roof -ceiling and the water during the summer; the panels cover the water ponds during the daytime and their aluminum coating reflects the solar radiation back to the sky. On summer nights, the insulation is rolled away and cooling takes place.

17 Fig. (3) shows the house originated by Dr. Felix Trombe .

- -Ai V **57

FIG 3 Trombe- Michel hoiue, developed for uve in Ihetouih of Friince. uiili .i Miuwivc concrete south-facing wall lived ns ihc heal absorber, insulated by double glazing, with con¬ vection space provided between the concrete and the glazing. The vertical south wall provides both heat storage and heating of the building at night. The system is passive, because the solar radiation is absorbed by a heavy concrete south-facing wall, which is covered with a single glazing. The concrete wall extends below the floor of the living space, and entry ports are provided which enable cool air from the floor level to flow downward, and then as the concrete is heated by the sun, the air rise in the space between the glass and the wall, and returns to the house through ports located near the roof . An overhang protects the wall from excessive insolation during the summer.

Another completely passive heating system is that used by Mr. and Mrs. David Wright. In the house constructed with heavy double adobe walls, with insulation between two

12 in. thicknesses of adobe block. The floor is also made of

24 in. of adobe, with insulation below it. The roof is heavily insulated, and the entire south wall consists of double-glazed windows. An overhang shades the windows from the summer sun, but permits the low-angle winter sun to

it enter freely. In order to seal the house against heat loss

at night, a horizontal insulating curtain is provided, which

can be retracted into space at the top of the window during

the daytime, and then lowered to any desired extent to

control the admission of solar energy in season when the

house would tend to be overheated without this provision. At

night, the insulating curtain is lowered completely, so that

all the glass is covered, and the combination of glass and curtain achieves a very high insulating value. j.if Active Systems:

Most of the hundreds of solar-heated residences

built throughout the would use the active system, in which

separate collectors are used to gather the solar radiation,

transfer it to air or water, and store it in tanks of water or rock piles, or both. The air and water are circulated by

fans or pumps, and conventional means are used to distribute

the heat to the interior of the residences. The oldest of

these in terms of operating history is the structure shown

in Fig. (4) which was built by Dr. George Lof, one of the

pioneers in the solar energy.

m inr H«I

V

house, erected in Denver in I9ÿS TW« k.,nif r i collectors are T h nls °r °vcrÿppinc: ass used to warm dr which in » k . *1

/

The collectors utilize glass plates, with the upper half transparent and the lower half blackened. The plates are set at an angle to the direction of air flow, so that the solar radiation, entering through a cover glass, also passes through several thicknesses of clear glass and is then absorbed on the blackened lower segment of each glass plate the heated air is blown through two large cylinders which are filled with rock approximately 5cm (2 in.) in diameter. This constitutes the storage system, which is charged up during each day.

One of the most successful and simplest solar heating systems is that devised by Dr. Harry Thomason of

Washington, D.C. His solar system uses an open-flow collector made of corrugated aluminum sheets that are painted with a waterproof black. A single cover glass is used and the collector is mounted directly on an insulated and water-proofed roof Fig. (5) . The primary

W h

b -no. S' Tin; Thomason residence in Washington. DC, which uses the system shown in I IO provide healing hy relatively low-temperature sun-warmed water. This house now has more than eighteen years of experience to demonstrate it* feasibility,

SLo storage is a 600-gal water tank, located in the basement of the house, and this is surrounded by some 50 tons of rocks, which provide both additional storage and a very large amount of heat transfer surface. The rocks are warmed by the outer surface of the tank, which in turn is heated by the sun-warmed water. A differential thermostat with one sensor fastened on the collector surface and the other in the water tank directs the pump to start whenever the sun has warmed the collector until its temperature is above the temperature of the water in the tank.

The water is pumped to a distribution pipe at the top of the roof and runs down by gravity through the troughs of the solar collector. The system is "fail-safe," because the water drains from the collector whenever the pump stops for any reasons . Warm air is used as the heat transport medium, and this is circulated by a small blower. For summer operation, a small compression refrigeration system issued to cool the water in the tank. A compressor operates only during off-peak periods, and cool air is circulated through the house during the daylight hours, when air conditioning is required. Fig. (6) a, b shows a cross section of the

rasirr-JK.

rrv iy l«l T“ T /

*******

X4> IlMf •* Py a i

'W Malt K«k >UTMJ Mi'h ka«‘ -l~* w 10 -4m ' K-M Solar system and an open-flow collector.

A number of active solar-heated and cooled residences are now in operation. The use double-glazed high- performance flat plate collectors to heat water freezed with ethylene glycol or a similar substance. In winter, the water issued directly in the heating systems of these building,

and in summer, the hot water is used to activate a lithium bromide absorption refrigeration system. Introduction of a practical sun-following concentrating collector using a linear Fresnel lens. These systems offer far more promise of

receive a substantial amount of direct radiation until close

to 0900 h on a summer day. The sun moves again to the

northwest by 1500 h, giving only approximately 6 h of

collection time. The concentrating collector, on the other

hand, can turn towards the east and pick up the early

morning solar radiation and follow the sun across the sky

until it is about to sit in the northwest. /.S'. Solar Houses as studied by Harry E. Thomason. Solar energy system has supplied most of the

heat requirements for the house despite half -cloudy winter weather and temperatures well below zero Centigrade (often

between 0 and 32 F) . Water from the 600 gal steel tank is

pumped to the top of the solar heat collector. There, it is

distributed in small streams to hundreds of valleys on the

black corrugated solar heat collector sheet. As the water

flows down in the valleys it is warmed by solar energy passing through the transparent cover. A gutter at the. bottom collects the small streams of warm water and passes

it to a 275 gal domestic water preheater tank and thence to

the main tank in the heat storage bin.

The warmed water, in addition to pre-heating the domestic water also warms the three truck loads of first¬

sized stones around the main 1600 gal tank. Then, when the

living quarters need heat, the thermostat automatically starts a 1/4 h.p. blower. This blows air through the warmed stones and around the warm tank of water thus warming the air. During the hot summer, water was pumped at night up

to the north-sloping roof section (U. S .Patent

No . 3, 254 , 701) .The tank of water and surrounding stones were thereby cold. Then a reverse-acting thermostat turned the blower on to circulate air to the bin . The solar heat collector is smaller (about 560 ft2 vs about 800 ft2 for solar house No.1) .However , a reflector of ordinary aluminum roofing was placed, at bottom to

increase solar input and solar heat collection by about 15 per cent . "Chimneys" were built behind the collector to take

excess heat to the attic and reduce the closet temperature (U.S. Patent No . 3, 254 , 703 ) . The "chimney" performs as anticipated, and the closet do not heat up. However, a

disadvantage sometimes arises during humid autumn weather. The closets remain very cool . Warm humid air enters the cool closets. At times the moisture condenses causing mildew in.

\ . £3 the closets. Therefore, warm air must be admitted during some humid cool periods of autumn to avoid mildew. The heat collector is installed entirely on the roof. The winter sun shines into the living room and swimming pool windows on the south side. The heat storage bin was modified by building the water tank of a concrete block. It makes it possible to install a tank simply even in an existing basement without removing a basement wall for a large steel tank. And the concrete blocks are not subject to rusting or corrosion.

Disadvantages include a reduced heat transfer rate from the warm water to the stones and to circulating air in the heat bin. The cooling systems is designed to alleviate the need for high power requirements during brownout. Also dehumidification and "dry" storage are achieved. A standard 3 h.p. compressor unit refrigerates a cooling coil in the ductwork ahead of the heat (Cold) storage bin. This dehumidifies the air and chills it as it is blown into the "cold" storage bin. An A-Frame design sets the heat collector area at a 60 degree slope and the entire side-roof is available for collector area. In this design half of the house support the collector, and The solar heat collector is small (about 560 ft vs about 800 ft for Solar House No .1) . However, a reflector of ordinary aluminum roofing was placed, at the bottom to increase solar input the collector serves as a roof and wall thereby reducing overall construction costs.

A new type of collector, using black, asphalt

& 4 shingles as the collector sheet . Water was pumped to the top and discharged in small streams about 2 in. apart.

Theoretically the streams should spread out and wet the entire hot black shingled surface to thereby heat the water.

However, spreading was not complete. A detergent (wetting agent) was added to the water and spreading was fair, but some areas remained dry and unvisited by the water. Instead of a water tank surrounded by stones in a bin, a "pancake" water tank was constructed. A two inch bed of sand was placed on the leveled ground under the floor. Two types of insulation were placed on the sand and inside of the foundation walls (Polyurethance and foamed glass) . A linear of polyethylene was draped over the foundation walls to form a shallow tank.

Like the Hay-Yellott system, this system uses a rooftop pond/8/. However, in the Hay/Yellot system insulation is physically moved over the solar warmed pond each night. Heat from the warm ceiling warms the space below. But heat is lost from the warm roof pond through the insulation all night long because no insulation is completely effective. In the author, s systems the solar warmed water flows by gravity to "Pancake" heat storage under the floor. The floor is thereby warmed. The rising heat warms the living quarter above.

In the system a small pump, pumps the water to the pond, only 8-9 ft above the heat storage tank, within 30-60 min. A pressure of only about 4 lb/in is adequate. Thus, very little pump power is required to pump the water up to

the pond each morning, and no power is required to allow it

to flow back down at the end of each day. In the Hay/Yellott

system the solar flux is de-concentrated in the winter. This

is because the rays come in at a low angle, say 30 45 ,

and are spread out over the entire large horizontal pond

area. The solar flux is only about 50-70 per cent as intense

as it would be if the sunlight were shining directly on a

surface normal to the sunrays . This means that the rays are

deconcentrated and the pond must therefore 50-100 per cent

large to intercept a given amount of solar heat . Such a large pond loses substantial amounts of heat upwards during

the day because it is radiating from is large are to the cold sky in a full hemisphere, and because cold winter

breezes are skimming the top of the transparent cover over

the large pond. The large pond also loses some heat at night

through the large insulated area, which cannot be completely effective.

To minimize this drawback the size of the roof -rope pond is reduced. A design for a large flat roof house or other building which permits considerable architectural deviation. Ponds No.1,2,3 and so on are fairly narrow in the north-south direction. Relatively short reflectors Rÿ , Rÿ , etc. are adjacent to their respective ponds. The ponds may extend the full length of the building in the east-west direction.

26 The figures showing solar houses are attached.

\ \ x *

\ JUS- —X//«- -r- 11 Ml :.«rt ! !»®iasi' ayr. kM kww N# I knH ft* *-»*« TktFHMÿlMIMWlbMNk mm,, T*

o y.>V SK-t; “7“ • Wj ./ OBB "s M

L< i u JT"'L *•- >» h,i|4 i bon >k* W*»*1 »W r-.i - Kÿn« nt< >W| / Dec.-Jan " Sun o\

N N. V R* 30"/ '• > J<_ Y Pond No 1 -tr~Pond No 2 jfcsn South

CA Fig. .A series of rooftop ponds and reflectors

Further the status report on the Sandia solar energy program by R.P. Stromberg reveals following experience [1, 2, 3] . Since July 1972 Sandia Laboratories has been undertaking a series of systems studies directed at

£ 7 evaluating the potential of solar energy as a partial

solution to the national energy problem. The goal of these

studies is to provide a system which (1) could save significant amount of fossil fuel, (2) could be economically competitive with the existing energy systems, and (3) could,

at the same time, minimize harmful ‘effects on the

environment and remain architecturally attractive. These

studies have resulted in the development of a concept designated as the Solar Total Energy System or a Solar Community in which a variety of techniques compatible with

solar energy concepts are combined in integral parts of a

residential, light commercial, and light industrial solar energy community. /.£. Solar Total Energy Concept: The solar community concept is an energy system

which attempts to minimize the use of fossil fuel energy in

a community by making maximum possible use of the energy

collected by a system of solar collectors Fig. (7). In this

baseline design, energy is collected at high

SOLAR COLLECTORS (FOCUSED) rossu rua rossu run ELECTRICITY HIGM TEMP BOILER r*- TURBO-GIN _ J r t - HEAT SOIAR { TEMPERATURE V >- l VÿSTORACtJ EXCHANGER TURBO-GEN; ELECTRICITY

COOLING TOWER WASTE HEAT

f ABSORPTION LOW TEMP SPACE COOLING STORAGE ) AIR CONDITIONING ICHIUEO WATER) FOSSIL FUEL AUX HEATER HOT WATER HEATING SPACE HEATING

'WATER DOMESTIC HEATER HOT WATER Fig-Y Focused cascaded total energy. temperature, stored in a thermal reservoir, and used to

produce electricity. After use for producing electricity,

the remaining thermal energy is either stored in a lower

temperature thermal reservoir for later use or distributed

immediately for heating, air conditioning, hot water or

i process heat.

Recent studies of the economics of thermal distribution show improvements in economics when activities using relatively large amounts of low-quality process heat can be integrated into the community plan. With the improved mathematical model now under development, an effort will be made to find the optimum max of loads for such a system.

The plan for the Solar Total Energy Program includes a solar total energy test bed which will be used for evaluating the general concept and for supplying the energy needs of a solar project building Fig. (8). The program will continue through

y «fll>:ii*1 connet. at 1 1 1 / i y /

II0«WC

iSolti loti!CIKflir several phases and will conclude with the construction and operation of a solar total energy opilot plant. The test bed will be constructed at Sandia Laboratories near the building

£9 presently housing the technical staff assigned to the Solar

Total Energy Project. The test bed is being designed to be as flexible as possible in order that it can be used to test a variety of energy systems and component part developed as

part of solar energy projects at other locations as well as

at Sandia.

A major part of the Sandia program is the

construction and evaluation of a "testbed" designed for

operation of loads approximately equivalent to 12-15 homes.

A first part of the systems analysis program is the

construction of a mathematical model of the test bed and the studies conducted to determine its operating

characteristics. A 1000-home community has been chosen as a

baseline for first analysis. Various parts of the system

will be sized for minimum cost, and a first series of

optimization will be performed on the cascaded system. In this case, as well as in all future cases, comparison will be made between the fuel savings and relative costs of (1)

the baseline design, (2) a fossil-fuel total energy system and (3) conventional practice as applied to the same

community configuration. How water and electric load

profiles and weather and solar data for different

geographical locations will be used to determine the fuel

savings and economic effects of construction of solar total O'- energy systems in different geographic locations. >$preiSmSftary studies of the Solar Total Energy n conceptÿjhave shown it to be more expensive than conventional 6/ . uses of fossil fuels at current prices. An effort will be made to extrapolate the future costs of fossil fuels and services in order to estimate the relative economics as changes occur in the relative cost of fuels and services. A user may assemble a group of mathematical models, prepared as subroutines, first specifies a name for a subroutine which models an individual component and then identifies it by a loop number and component number so that the parts may be assembled in the proper order. By specifying the upstream component and the numerical values for the parameters used in the subroutine, assembles a loop. The program connects a series of components (outlet of one component to inlet of next component) to form a closed loop for fluid flow.

Initial outlet temperature, pressure and mass flow rate are specified for each component. At each time step, information parameters are computed and applied to the component subroutines. From these parameters, equilibrium temperatures and heat transfer rates are calculated.

When equilibrium conditions are determined, time is incremented and equilibrium heat transfer rates are integrated to calculate new temperatures in components such as storage units which cannot be assumed to operate at equilibrium. At this time, new information parameters are given to the components, and the process is repeated.

It is important to note that the system is treated as a "quasi-equilibrium" system, that is, those components with large heat-retaining reservoirs do not have equilibrium

31 models. A diagram that summarizes the computer program is presented in Pig. (9).

I •re I GO ! El pH

Gil I r*rH=»*l;griiÿr |- f E.'S'*' )J‘ f,*JL Economic analyticcomputer program.

The output is a figure referred to as the annual revenue requirement, which is the average amount that must be received each year to cover the economic cost of the project under consideration. In the case of such nondepreciable assets as hand and working capital, only the cost of money used for their acquisition is required. The value of these items is assumed to remain in the business, and additional cash outlays are not required. In the case of depreciable assets and future costs, a recovery factor is applied that takes into account the need to recover cash as well as provide a return on money invested.

Valid economic comparisons between alternative components within the system can be made with this program.

When the total system is compared with other energy systems, the annual revenue requirement must be converted to a cost per energy unit-cost per dwelling, or some such common denominator that can be determined for both system. A system design which incorporates 1000 identical

residences, focusing collectors, a high and low-temperature

thermal storage system two auxiliary fossil fuel furnaces,

a turbo-generator, and a load composed of 1000 identical residences has been selected, and analysis of the system has

been initiated. One hundred and fifty 9.15x15.25m focusing

collectors mounted in N-S orientation and elevated to 40

collect solar energy and heat Therminal 66 fluid to 590 K.

This energy is stored in a 1000m high-temperature storage

unit (sized for overnight storage) for use by turbogenerator

which operates at a boiling temperature of 510 K and a

condenser temperature of 380 K. The Therminol fluid is

returned from the turbine to storage at 460 K, and heat is

rejected from the turbine condenser at 380 K to a 1500m . Cooling towers are included to dissipate the energy during

periods when the storage systems are full. From the storage, the water travels through an insulated pipe distribution

system to the individual homes and is returned to storage

after undergoing pipe thermal losses and a 30 C temperature

drop at the home. The homes are uniform, with an area of

139 -5m each and are spaced 36.5m apart. The ratio of total

house- to-collector area is approx. 6.5:1.The average daily

electrical load is 0.83 kW per house. Economic analysis have been completed with the results shown in Fig. (10) . w*

z S'"; ----— §v srvan IVLAUCN vou * M wo MUG 19 H il •« 11 *9 10 t l* k-t M *»!_1_I L- I W K__» Hut n i>f VvH jvul onl» tofivi n Miter \

A few curves from the preliminary runs of the computer program will serve to illustrate its operating

characteristics under summer weather condition. The first

two curves Fig. (11 and 12) shown inside and outside

10in |*OfcT will* ta«« ruAi iu»> tntiu w« xmu •AN ***** or(iui>ON

oum« IUU inn Hwnt*iu*( •? ». ma • S , I W- S' L S l -i 5 s 5*.\ wttWHCATÿat ’i »*C" ll»J»l

t—t— lill/nu two ujifciif +-t~* luwvia 'Hi/ll* •JOW * Ai*hwu»Q«lbi»»UM»|Uiiipcis*w*-

temperatures of the house and the energy content in the high and low-temperature storage. The inside room temperature shows a sharp decrease at 2 and 4 p.m. when the air conditioning system is energized.

Fig. (13) shows consumption of fuel by the fossil- T J J e f- f

1 i fuel heaters to supply the high-temperature and low- temperatures storage reservoirs. As indicated in Fig. (12) . the high-temperature storage reached its lower limit at 3 a.m. Starting at that time the high-temperature fuel is

burned to produce electricity. The shape of the consumption

curve for high-temperature fluid heating matches the

electrical load demand in the home for 3-7 a.m. By 7 a.m.

the solar input has reached a level high enough (750 J/m sec) to take over operation of the turbogenerator, and the

fuel for high-temperature fluid heating in cut off.

As an aid to the process of designing solar collectors and collector arrays, a computer simulation has

been developed. Basically, the graphics system provides a

tool which the designer can use to analyze in real time the

performance of both collector arrays and individual

collectors. Many different options can be tried in a short

time in order to build understanding and intuition. One form of output is a perspective view of a collector array as seen

from the sun. The example chosen is for an array of 20 single-axis tracking parabolic collectors at a particular time on the summer solstice day. Fig. (14) shows the

fractional projected area for a single collector (i.e.the so-called cosine effect)

m •r.iutntt ir&

.1) h \ CMItaUllOh

PH j_ fc fr t IMf [UrucifcJiJ pn'jA-vd jrra an utaj d W lraciia|

3*f as a function of time on the summer solstice day. It can be

seen that although the E-W orientation is always normal to

the sun at solar noon, the N-S orientation is superior when

averaged over the entire day. Shadowing, which is always

present to some extent in early morning and late afternoon.

adds an additional penalty to projected area. Fig. (14) shows the fractional projected area for a

rectangular array of 20 tracking 9x12 ft parabolic

collectors spaced 24 ft center-to-center. The N-S orientation is sen to suffer more from shadowing than does

the E-W orientation.

Figs.15 (a) and (b) show the power output from the system when solar intensity, projected area, shadowing and collector efficiency are included. Energy collected with N-S orientation is 2.32.MBtu on the winter solstice as opposed to 2.092.09 with E-W orientation, a difference of 10%.

As a result of these and other studies, a choice of

E-W collector field orientation was made. These results could be test and if found possible could be implemented in this area having slight similarity in geographic and climatic conditions specially in two intense seasons. The operational modes of solar heating and cooling as described by D.S.Ward [4] :

Of primary concern in the choice of operational modes is the fact that solar energy availability is not necessarily in phase with heating and cooling demands, nor with the system' s ability to effectively utilize the 3/ incident energy D.S.Ward. A properly designed solar heating and cooling system should, however, automatically compensate for the variations between solar input and load demand. This includes all the factors that are responsible for extraction of heat energy from the solar collectors, storage of this heat, and delivery of the heat to the loads as required. The guidelines for these objectives are to minimize the use of auxiliary fuel while maintaining the space comfort and service hot water equivalent to that of conventional fuel energy systems. Decisions are also required in the design of subsystem component arrangements and component types while progressing toward these objectives.

Solar heat storage is accomplished by sensible heat storage in a non-pressurized tank of water, it may be desirable to dump excess solar heat from the storage tank by vaporisation of the storage tank water. In the Colorado

State University design, heat rejection, which is prevalent in the spring and fall of the year when neither the heating nor cooling loads are high, is accomplished by venting of the vaporized storage tank water. A vented storage tank can create pumping difficulties that are most prevalent in the cooling mode when water must be pumped to the generator at 77-95 (170-203 F) . Operating in this range (near the local boiling point of 203 F) , only slight deviations in pressure can produce vapor locks in the pumps. The manner in which auxiliary heat is supplied affects overall system performance and cost. Auxiliary heat may be used to boost

3? AUXILIARY HEAT.

Fig. Auxiliary heat in series with storage to load. *

T AUXILIARY

Q 0 H AUTOMATIC— VALVE Fig.If.Auxiliary heat in parallel with storage to load.

“\ : STORAGE *3 I LWATER TANK an i [TANK from cold main Fig./ff Once through solar hot water heating.

from cold main

r STORAGE -*—i ; rf'M « • TANK J : :! — I LLJ• PREHEAT HEATER STORAGE Fig )jStorageof solar heated hot water.

3& the temperature of the hot water coming from solar heat storage as in Fig. (16) , if the temperature of the solar derived heat does not meet the heating of cooling requirements or the auxiliary may be used to meet the full load when ever the storage temperature is too low to be useful Fig. (17) . A fault in the first method can be shown by examining the system when used for cooling. If the storage temperature is 77 C (170 F) , the auxiliary could be used to raise the terpperature of the water to 87 C (190 F) , a 10 C

(18 F) rise. But the water temperature drop through generator is only 6 C (170 F) thereby using some of the storage heat capacity to store fuel energy. Service hot water may be heated from solar storage water by a once through heat exchanger as illustrated in Fig. (18) Because service hot water demand is intermittent, such a process requires a high capacity heat exchanger, which would be ideal most of the time. A preheat tank such as illustrated in Fig. (19) is preferred for several reasons. With continuous flow through the heat exchanger, more solar heated service hot water can be utilized.

In both case water from the solar preheat tank is delivered to a fuel fired hot water heater, where it is heated further if it does not reach the required temperature in the preheat tank. A possible modification is illustrated

•W

V. OIMt’JAMii*, t V*.

JOJ Mi \ S »»-li ' .'HXm VI .•11* AM Vli’J'llI

r? AM v: ' -i J i i? i i r~ f- t A' lr r— . - ILVt — Jfj!) — % I I'uwcr for an wrny of .'It Ir.ukiiiy piraMic eolUuo— t N dft paraMi*' — liy Power for ;m army of :n rwUnp the winter niKliee. uiinnurr \»»Micc. the / '9.O0*J / --- 31 in Fig. (20) . Here the solar hot water preheat tank is

SOLAR COLLECTORS /.

SUPPLY AJR K AIR HEATING COILS m .STORAGE;'! Wm, TANK /, MM RETURN AIR —. D ABSORPTION AUXILIARYiiiuiia HEAT' AIR CONDITIONER BOILER EXCHANGER Fitjp Mode 1—Solÿr collection using heat exchanger. installed within the solar heat storage tank. This eliminates heat losses from the solar hot water preheat tank. The disadvantage of this modification is that the solar heat storage tank will under some conditions, approach the boiling point, and result in the delivery of service hot water at scalding temperatures. It is imperative that this high temperature be lowered by some means such as an automatic mixing valve. Four of the most probable modes for cost effective subsystems operation were provided as options. Mode I is characterized by the use of a heat exchanger that separates the collector liquid from the storage tank liquid. Fig. (21) illustrates with hold lines

from coid water nna»n

Automatic Mixing So*ar not Valve water Pre- U- .- Tank U Solar Heat Conventional Storage lank -Hot Water Heater

solar heat Solar hot water preheat tank located within R*-i| 11 rage tank. LfO the liquid circuits used in Mode I. The two main advantages of Mode I are avoidance of antifreeze in the storage system and the use of a non-pressurized (vented to the atmosphere) .

The use of Mode I allows for the possibility of a pressurized collector circuit and a non-pressurized storage tank. With the heat exchanger acting as a pressure barrier, the collector loop can be completely liquid-filled. In addition the collector loop has no gravity head loss for the pump to overcome (only frictional losses) . To "spill" the fluid from the top of the collectors to an open storage tank ( a height of 7.6m (25 ft) for Colorado State University

Solar House I) , would require doubing the collector pumping power. Corrosion protection of the aluminum collector absorber plates is also a major consideration in the choice of Mode I. The need for continuous filtration of the collector liquid is necessary in any multimetal system.

Finally, Mode I permit a wide variety of collector. Mode 2 provides for collected solar heat to be delivered directly to the storage tank. It does not utilize the collector heat exchanger or the storage pump required in Mode I. Fig. (22) illustrates the liquid circuit. There is the saving of

SOLAR COLLECTORS

SUPPLY AIR

AIR KEATINO COILS f 19 >STORAGE>>mm Q

RETURN - AIR —i. capital equipment and maintenance costs for the collector heat exchanger and the storage pump. The temperature drop across the collector heat exchanger (ranging from 0 to 6 C) is eliminated with a net result of an improvement in system efficiency. Mode 3 is a cooling design that does not utilize heat storage, but supplies solar heated fluid directly to the generator of the air conditioner. Fig. (23) is a diagram of this mode.

/y 1

It

AIM AT II

ITfAACr ru« C)

At TUAN [ Art 1 t, — yy- tSVmriK# HiIN f )tu/ r

The advantages of Mode 3 are higher water temperatures available to the generator of the air conditioner and the avoidance of some heat loss into the house from the storage tank, the avoidance of storage tank mixing means that Mode 3 can provide higher temperatures to the air conditioner generator and thereby increase the cooling output refer to Fig. (24) Two disadvantages of 11 7 / yf-- Wil* Ayp«A 7 10 flON / ThrCKjO* A®- j •own / .....y. t f / / I * h z* /// 3 tt Vj &f/ V 17l S’ - j

fti 90 Mode 3 are poor cooling control due to solar input variations that are directly transmitted to the air conditioner, and the lack of stored energy for cooling in the evening. In the heating season, there will often be a condition in which the storage tank temperature is considerably above house temperature, but is not high enough to carry the entire heating load (Maintain the desired house temperature setting) . It is particularly desirable to use this heat at moderately low temperature because it is acquired at high collector efficiency. The liquid-to-air heating design allows for separate solar storage and auxiliary boiler loops to supply heat in the air duct. This arrangement is illustrated in Fig. (25). SOLAR COLLECTORSÿ?' SUPPLY AIR

AIR HEATING COILS T*

RETURN - « > AIR .. & WA- —ABSORPTION AUXILIARY HEAT The solar air heating coil is placed ahead of the auxiliary air heating coil in the direction of air flow. The solar coil thus preheats the air while the auxiliary coil boosts the air temperature to that required to maintain the heating load. The alternate mode can be expected to be most useful in the coldest months. During most of the heating season, however this was not drop below 38 C(100 F) until the end of

43 December. Thus to evaluate more properly the effectiveness of the mode we must consider the full heating season, must consider the full heating season.

Similarly the solar air system of Colorado State University

Solar House II includes:

(1) A flat-plate solar air heating collector {68.4m

; 376 ft ) with air passage beneath a black coated sheet plate, internally manifolded and insulated, and covered by

two glass panes.

(2) A storage unit with 20 tons (18,200 kg) of round and crushed 1.9cm - 3.8cm (0.75-1.5 in.) rock which is supplied with solar heated air in winter and evaporatively cooled night air in summer.

(3) The building space conditioning control unit which includes the sensors and control logic necessary to automatically maintain comfort at all times.

(4) The air handling module including air ducts, automatic dampers, filters and blower. (5) The solar hot water unit consisting of an air-

to-water duct coil heat exchanger and a preheat storage tank which is connected to an auxiliary hot water heater.

(6) A day-night evaporative exchange cooler with outdoor air inlet and exhaust duct and

(7) An auxiliary heating unit to meet maximum space heating demand when storage temperatures are insufficient or when the solar system is not operating.

44 Under practical operating conditions, efficiencies of solar water heaters and air heaters are not greatly different. This is demonstrated in Fig. (26) , where theoretical plots based

70

60

£30 u

LU s 30 3! S 20

10

30 60 90 120 Fjg-2& ’ TCo(P.elor Ovlltl ~ TftaaMtni ) • *C

on thermal characteristics of liquid and air heaters are presented for double glazed, flat -black collectors under conditions of incident solar radiation.

These curves show that at the selected conditions and a typical AT of 50°C(0°F), there is a difference in absolute efficiencies of about 7 per cent. An air heater with smaller air passages could show a higher efficiency than a liquid heater, but more power would have to be used far air circulation. The collector efficiency is plotted against the difference between the outlet temperature at the collector and the atmosphere. Outlet temperature is used because of the large air temperature rise through an air collector, which may average 40 °C (72 °F) . The liquid collector, on the other hand, seldom operates above a 10 °C (18 ° F) temperature rise. Since outlet temperature is more significant than inlet in comparing usefulness of collected

heat, comparisons of performance at equal outlet temperatures are the heat measures of heating capability. In addition to these distinctions between liquid

and air collectors, the air collector performance is also a

strong function of flow rate. In Fig. (27) , collector

DOUBLE GLASS 2 ft COVERS ‘ h BLACK SI/TFAC M?*ATL EDGE SUPPORTS SECET C— m METAL AIR DUCT — •V

FEERGLASS INSULATION

efficiency is plotted against air flow rate through the collector. The solar air heater involved in this experiment and analysis consists of two glass covers, an air passage

2cm high and 4 m long under a black metal absorbing surface, and a layer of insulation

Fig. (28) . Heat is extracted by the air in the space between

>!•

100 ro s~ r !- iii ! i I K

Am 1 " MMW*4 iMtm • — rt M** Am r»Rw,******* + ***** the black absorber plate and the insulation. Theoretical analysis of the heat transfer characteristics of this design yields a value of Fr = 0.70 at an air flow rate of 0.01 m2 /sec.m2 of collector (2 cfm per square foot of collector) in the equation.

<*u “ AcFR ts-UL (Tin “ Tambÿ where

4 7 freezing or corrosion risks are encountered. Heat loss from storage is acceptable even with limited insulation on the bin surface. Fig. (29) depicts the time-temperature position

i yy A, 1° ri ri

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circulated through the collectors usually with a mid-day temperature rise. Cool air from the building is returned to the collector for reheating. The hot water heat exchanger is in series with the collector at all times and provides preheated water whenever hot air is delivered from the collector. When heat is being stored solar heated air is routed through the pebble bed as in Fig. (31) , thereby rrvsr

k pi is.— 31 osv/j

(at g 'cr?

c:r" 'IE Pi heating the pebbles, while the cool air returns to the collector for reheating. In the evening and nighttime hours, heat is delivered from storage by circulating air from the building Fig. (32) .

s. is.— MO

O, .f"T IHP?*

Li;- /•$J* it5ÿ The system automatically provides auxiliary heating from fuel or electricity when solar heat from either the collector or storage is at too low a temperature to meed the demand. The system is designed to utilize the normally cool night air an evaporative cooler and storing cool rocks in the pebble bed as depicted in Fig. (33) .

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The primary objectives of the project for Design and construction of a residential solar heating and cooling system are to:

(1) Establish the practicality of space cooling with solar energy. (2) Design an effective and economical system for residential heating and cooling and service water heating with solar energy.

(3) Construct a fully automated and instrumented solar heating and cooling system in a new residential building.

(4) Appraise the performance of the complete heating and . cooling system and each of its principal components.

(5) Determine which of several operating modes minimizes auxiliary energy requirements.

(6) Appraise the utility of a mathematical model in design and prediction of performance by comparing actual and predicted results.

(7) Modify system design and operation to minimize total annual cost of heating and cooling.

To accomplish these objectives, criteria for system design and performance were established as follows:

(1) Conducting a proof -of -concept experiment and demonstration with an optimized system of predictable satisfactory performance with currently-known technology.

(2) Utilizing a building design which has "typical” rather than "extreme" or "unusual" appearance, size form, materials energy requirements, insulation, fenestration and all other characteristics of a modern single family house.

(3) Providing at all times a comfort level in the building fully equal to that obtainable with the best conventional heating and cooling systems.

(4) Designing the building and the heating and cooling system so that the solar collectors and other components can be easily replaced with completely different units for testing after the present system has been fully evaluated.

(5) Designing a collector for mounting on the roof surface but also suitable for modifying and roof replacement.

(6) Designing a system which will carry about three- sr quarters of the annual heating load and three-quarters of the annual cooling load with solar energy. (7) Providing sufficient flexibility and "redundancy" on the heating and cooling system to permit comparison of several variations in design and operating method.

(8) Employing commercially available controls in a fully automatic system requiring no human intervention other than setting a wall thermostat for the desired house temperature.

(9) Assuming reliability, durability, and safety consideration take priority over least cost incentives in this experimental installation.

(10) Minimizing system cost without jeopardizing performance or durability.

(11) Utilizing only those designs and materials which could provide low cost solar energy with high volume manufacture.

The result was a modern three bedroom frame residence, with a living area of 140 m (1500 ft ) and a full, heated basement. The solar heating and cooling system is shown in simplified form in Fig. (34) . It uses "conventional" lithium

i i ~r ESD <2.

f 3 Uli 7r_ ! i IZrJ-i r i I i <>~*sr1 *—ILJPÿH f> — — ! I

t <#4 bromide absorption cooling unit, hot water boiler, air heater coil, hot water heater, and associated piping, ducts,

pumps, etc. The solar components consist of a solar collector and pump, thermal storage with heat exchanger and hot water reheat tank, and an automatic valve. Fig. (35) is a cross section schematic SO'. *R ENERGY HOUSE Mold Air Condilx**"* . Mol [quiptnini Ui«>

m « riyoi Mlltlliq C#rl* !' LX U ll rÿr ______.•“ÿsa.wsrt'- U r in — __ Of*4-• '*! W#'1 Wlirx

A An Vi*. •oc**- ! *•« is \ I ru Ml . I i T«** rrir—

(2) storing heat directly from the solar collector. In both cases storage then supplies heat to the heating or cooling unit; if storage temperature is insufficient, the heating or cooling load is supplied by the auxiliary boiler. A third mode of operation is by heat coming directly from the solar collector to the heating or cooling unit. The hot water heating system utilizes solar storage for preheating service hot water. Water enters from a cold water main to a preheat tank, which supplied heat from storage by circulation through a heat exchanger. On demand the preheated water then

53 goes to a conventional gas hot water heater, which maintains

the required temperature. Because of the experimental nature of the installation and the need to replace the collector with new designs at a later date, a watertight sub-roof was made an integral part of the house design. The design / CD / selected is shown in Fig. (36) . / / 7— C«*ir CIQM

1—f C—«r I 777T / JOE Jr / //. AllMtll / V 7/

The collector is composed of aluminum structural supports, two sheets of B-quality double strength (1/8 in.) window glass, an aluminum absorber place with internal tubes

(’’Roll-Bond" ), and insulation beneath the cover places are attached to the aluminum structure by a beauty tape and an aluminum cap strip. Approximately one-third of the glass covers have undergone an unit -ref lection treatment. The aluminum panel has a tube pattern of parallel flow in multiple straight tubes between internal sloping manifolds. A flat-black "Nextel" acrylic coating was baked on the aluminum surface at a temperature of 204 C (400 F) . The insulation consists of 2.54cm (1 in.) unbounded glass fiber mat on a 3.81cm (1.5 in. ) ( " Fesco-Foam" ) composite insulation. The use of aluminum for the structural components and as the absorber plate was predicated primarily on the basis of the metal's availability,

5% durability and cost. A particular advantage of an aluminum

absorber plate over other metals such as steel and its

availability in the tube-in-sheet design. This type panel

contains tubes and headers formed within the sluminum sheet.

Thermal conductivity between the plate surface and the fluid

circulated through the tubes is therefore maximized. Another

advantage of the tube-in-sheet aluminum panel is versatility

in tube pattern design. Select on of a tube pattern

Figs. (37 and 38) is based on two concerns: rate of flow and

33750in *0 005 r' 1900in —0 200 I |---3Q00«i .IOOO A w A!- * 0016 IOOO to I 0979 m -ooeo 3 000 .n 0060 isOOo- 2* 0 0 r Section A-A --J ! 96000 in. 1 *0005 0 200 ii

— ;00i6 Long — 0-376 . 0f | *0 031 Tron* 1 la— *0 003 •*' \j 9000 in O 060 f I 500 in Viyll Section 8-0 drainage, provision for drainage of the solar collector

during non-daylight hours can alleviate freezing problems

and eliminate heat loss from the water in the collector at

night. The data we see that the higher angle (53 ) is closer

to optimum for heating, the lower angle (37 ) is closer to

optimum for cooling and the combination (Fort Collins is at

a latitude of approximately 41 ) From the this it was

decided to face the solar collector toward the south at a 45

> angle. Determination of the optimum collector area would

require additional information (e.g., fuel costs), so that additional costs of the larger solar collector could be

compared againBt the fuel savings. However, for this experimental unit it had been decided that the collector

should furnish the major option of the heating and cooling

load. The actual area of the collector was designed at 71.3m

(768 ft. ). To provide approximately three-quarters of the

heating and cooing loads and to allow for flexibility in

future solar collector testing, a collector 4.88m x 19.5m

(16 ft x 48 ft ) was selected. The storage medium is water with heat transfer from the collector loop in a heat exchanger. The container is a light gauge, vertical galvanize steel cylinder 1.83m (6 ft) high and 1.68m

(5 1/2 ft) in dia. It holds 4,275 liters (1131 gal . ) , a nominal 61 lm-1 of collector (1.5 gal .ft-2) .This size of storage is based on the economic studies of Tybout and Lof

[5] and conclusions readed by Duffie [6] and Yeh [7] .

Surrounding the tank is a bonded glass fiber double-faced batt insulation having an R. factor of 7-61

( Cm /w) , is far too costly to meet the full heating and cooling load with solar energy, so the essential requirement of storage is to accumulate solar heat in the daytime for use at night. The frequency of two or more successive cloudy days is not sufficient to justify storage of more than one day of midwinter heat demand. If more storage were provided, aditional collector area would also be needed to heat it

Si during the preceding sunny period.

/•?. Cooling System Design: Several systems were considered. These included: (1) Lithium horomode absorption.

(2) Ammonia absorption.

(3) TEG dehumidification and evaporative cooling.

(4) Solid desiccant and rock-bed regenerative cooling.

(5) Expansion engine with compression cooling.

(6) Open cycle lithium chloride absorption.

The criteria for the selection of a unit involved: (1) Immediate commercial availability.

(2) Compatibility with solar heat supply. (3) Capability to meet cooling requirements.

(4) Proven performance.

(5) Acceptable cost.

3-ton lithium bromide absorption cooling unit is

modified to utilize hot water (instead of natural gas) as

the heat supply to the generator.

A schematic drawing of the air conditioner is shown in Fig . (39) The generator in a gas-fired ARKLA machine was replaced

li I M ’i i : i. U -.'rf I I

HI* !**«(•

*|JU VlUliO

iMMl a • Mill W&1U•kit t>~7 with one operating with hot water entering at the bottom. Weigh cooling water at 24 C (75) F) , a hot water supply of

421 min (11 gal. min ) at 87 C (188 F) will provide the full 3-ton capacity is lower, reaching 80 per cent output at about 80 C (176 F) . Performance data is represented in Fig. (40) . In order that heat

200r* RATING POINT m*F COOLING WATER) ? CAPACITY Jj 190 lOO% ¥J SO % 1*0 £ *0%

19 170 1£ u s 160 5 II OPU TO GENERATOR 10 OPU TO COOCMG TOWER 2z 3

AO A5 50 55 GO M TO OUTOOOft WET BULB TEMPERATURE supply temperature slightly lowers than standard can be employed, the concentration of the LiBr solution has been reduced to 51-54 per cent, from the customary 54-57 per cent concentration. The unit has been modified also by the installation of a cooling water diverter valve for the absorber which is actuated by low temperature cooling water.

These modification permit advantage to be taken of prevailing wet bulb temperatures and, consequently allow an increase incapacity over most of the range of generator temperatures. As the air cooling capacity of the unit deceases (due to lower generator temperatures) , dehumidification performance also declines. Operating at full capacity, the refrigerant finishes vaporizing at point C Fig. (41) thereby

Evaporator ; M i M i ii n M ' | t?*frig»ront © / vl )

cooling the entire evaporator surface on which moisture condenses. At 60 percent cooling capacity the refrigerant finishes vaporization at Point B# so the condensate covers only the upper 60 per cent of the finned area. Air temperature reduction is then about 60 per cent of the full capacity, but about 10 per cent of the condensate formed on the upper portion of the finned area will re-evaporate as it flows down over the lower, uncooled, area. The net result is an air cooling capacity of 60 per cent.

The passive solar heating systems for buildings described by

B.Givoni with emphasis placed on the architectural design issues associated with the different passive solar heating systems to the problems that may be encountered when passive solar heating is applied in regions with hot summers.

The most common passive solar heating systems and a relatively new system comprise of the Barra (wall convective .

& loops) system. The solar passive heating are: - direct gain - collecting storage (Trombe) walls - wall convective loops (the Barra system) - various types of sun spaces.

In direct gain buildings the sun is admitted directly into the inhabited spaces through conventional windows, skylights, etc. In many buildings not all the rooms have direct exposure to the sun through windows or clerestories. In such buildings effective air circulation between "solar" rooms and "nonsolar" spaces is essential for achieving a high solar fraction by direct gain. In some circumstances, fan assisted circulation through openings in the walls between rooms, ducts or false ceiling, may be necessary to endure adequate heat distribution [8] . The main factors affecting the performance of direct gain buildings are: - orientation and location of the solar glazing - size and type of the solar glazing - the amount and design details of the mass available

for thermal storage.

- heat loss coefficient of the building as a whole

- arrangement of the furniture in the solar rooms

- thermal coupling between solar and nonsolar rooms - control options of heat gain and loss through the

60 glazing. Solar glazing, by definition, should face the winter sun. However, in reality, as the solar glazing of direct gain systems is usually determined by the orientation of the building itself, exact orientation is not always possible. Deviation of up to about 30 degrees from the true south and north, in the northern and the southern hemispheres, respectively, would not greatly affect the solar radiation impinging on the glazing [9] . The major advantage of the direct gain systems is that significant amounts of solar energy may be collected in the heated rooms through elements that would be found in the building in any case, namely windows, clerestories, and roof monitors (skylights with vertical glazing), facing the sun. Givoni

[10] has compared has compared the measured auxiliary heat in winter and the cooling load in summer in buildings with roof monitors in the USA., in a DOE monitoring program [11] . Increasing the area of the solar glazing in direct gain buildings increases proportionately the solar gain during the daytime but it also increases the heat loss through the glazed area during the summer. The ratio between these different thermal effects depends on the relative severity of the winter and the summer seasons in a given region, as well as on the properties and details of the solar glazing.

When the indoor temperature exceeds the upper limit of comfort, or when problems of glare and discomfort arise from direct explosure to the sun, the solar gain has to be

61 prevented by shading the windows or has to be expelled by venting the excess heat. Glazing is usually the weakest thermal point in the building envelope, causing excessive heat loss at night. From the viewpoint of solar energy utilization, the benefits from increasing the size of glazing is of diminishing return, while the heat loss at night through the glazing is proportional to the glazing area .

The penalty from summer conductive heat gain through a large area of solar glazing in regions with hot summers, even if the glazing shaded, may well be greater than the winter benefits. In some cases it may lead to the need to install mechanical air conditioning in places that otherwise do not need mechanical cooling. A summary of the experience with occupied residential buildings employing direct gain [10] , the following "rules-of -thumb" can give design guidance. Thermal mass stores energy from sunlit hours to be utilized during the night. From the point of view of the daily cycle, only limited thicknesses of storage elements, not all the normal mass in a building is effective for storage of solar energy. At present, the most common and cost effective materials for thermal storage are masonry materials such as concrete, brick, stone, etc., that serve structural purposes as well. The effectiveness of thermal storage elements depends on the rate at which heat is absorbed and later given back to the indoor air. Taking into account the undefined pattern of the radiant and convective flow of the penetrating solar radiation into the storage

elements, the minimum surface area of the thermal storage

elements recommended by Balcomb [12] is six times the area

of the solar glazing regardless of the thickness. The

overall effective capacity of a solar space to store excess

solar energy, is expressed by its diurnal heat capacity. The

concept of the diurnal heat capacity was developed by

Balcomb [12] and is based on the admittance concept, originally developed in Britain [13] . Mathematical models for calculating the effective diurnal heat capacity (DHC)

and its effect on the performance of direct gain buildings are presented in [12] and [14,15] . The actual energy saving from a passive solar system of a given size, solar saving

and the solar saving fraction it achieves (ratio of solar

saving to the total heating load) , increases as the building is of a higher heat loss coefficient (J/K day or Wh/K day) , namely with poorer insulation of its envelope. This is illustrated in Fig. (42) .

I & © SOLAR SAV1NC (Kwh/morilh) sjj ?f| ??isi sssiiiii HI H1 88 * 4 is s 5 © ©*:8 Ill K| "A, litIn X?! 1I a (i:. E>5:41 10 !> ‘I ‘I £ __\

• The solar saving fraction was computed (by the generalized model developed by the Givoni [14,15] as a function of the

& area of the solar glazing in buildings with two levels of the building loss coefficient. In buildings with direct solar gain through windows, the floors are often considered the obvious building element providing the main thermal storage since this is the element presumably most exposed to the direct solar radiation. In reality, however, the postulated capacity is assumed in calculations. The reason is that furniture and carpets in inhabited buildings usually block a large portion of the floor area from the sun.

Collecting storage walls combine in one building element, the functions of solar energy collection, heat storage, and heat transfer to the interior. This system was first developed by Felix Trombe and Jacques Michel at Odeillo, France in 1967, and is commonly referred to as a Trombe (or Trombe-Michel) wall. In its simplest form it consists of glazing placed in front of a sun facing, massive conductive wall (e.g., of dense concrete), with an air gap in between. The exterior surface of the wall is painted a dark color or given a selective surface [16,9] to enhance absorption of radiation. Solar radiation penetrating the glazing is absorbed in the massive wall, raising the external surface temperature and that of the air incontact with it. The fraction of the absorbed heat that is transmitted through the wall to the interior is determined by the thermal conductivity of the material and the wall thickness, as well as by the combined conductance of the air space and the glazing. The interior is heated by longwave

6h radiation and natural convection from the wall's warm internal face.

The major advantages of Trombe walls are: - The indoor temperatures are more stable than in most other passive systems. - Excessive sunshine, and its associated functional problems, does not penetrate into the inhabited space. - Installation is relatively inexpensive where construction would normally be masonry, or for retrofitting existing buildings with uninsulated

massive external walls. - Summer overheating problems may outweigh winter benefits in regions with mild winters and hot

summer unless effective shading, also from

radiation reflected from the ground, is provided. - In a climate with extended cold, cloudy periods, without adequate operable insulation, the wall

may become a heat sink. This drawback may be

minimized by the use of a selective surface, or

prevented by effective use of operable insulation or transparent insulation. - The effective heating is felt only to a depth of about 1.5 times the wall height, due to the limited depth of natural convection air currents

and the decreasing radiant heat flux from the warm, sun facing wall .

65 - In multistory buildings, problems with maintenance of the glazing may necessitage the

provision of access balconies. Note, however, that such balconies can function as shading overhangs for the glazing

below.

Thermal storage walls combine in one element the function of collection, transfer, and storage of solar energy. For optimal energy transfer through the wall, materials of relatively high thermal conductivity are necessary. For total energy saving, the wall thickness will have a small affect, but it can be an important factor for the indoor temperature swing and comfort . The higher the solar absorption of the external wall surface, the higher is the heat gain through the system. Black surfaces are often not acceptable architecturally. The most common choice is therefore a dark paint. Under optimal flow conditions, about 3 0% of the total energy flow in vented walls made of concrete about 30cm thick, is by convection and 70% is by conduction. A vented wall exhibits a lower temperature in the air space and consequently less heat is lost through the glazing. Therefore the overall efficiency is higher by about

10% in systems with vented walls as compared with unvented walls [17] . Some problems associated with vents are dust accumulation on the linear surface of the glazing and on the dark absorbing surface. Since it is impossible to remove the dust, it may eventually reduce the performance in addition

U to the aesthetic impact. The relative amount of solar energy

absorbed at a Trombe wall that is transmitted to the interior of the building (the heating efficiency) is

significantly higher in summer than in winter because of the

different relative temperature gradients from the absorbing

surface to the indoor and outdoor temperatures respectively. The point was illustrated f18] that the external surface temperature of a collecting storage wall, even when

the wall and a sidewalk in front of it were completely

shaded from direct radiation by a deep overhang, is elevated above the ambient air by up to 8 C (see Fig. (43) . Therefore it is suggested [10] that

PERFORMANCE OF SHADED TROMBE WALL IN SUMMER 40 M 38 iZ.\ b) f \ \ ;l 36 t- i <\ I II l i nI l‘. l I i T \\ .1 t i T I i / \\I li £ 32 r t [ $ n 1r \ i 30 w 1 S * i i \ i! *i k i / 3 •i n 28 - - * r m \ i \ Y i'-U: 1 * I l \ 26 r V i i i, hr I S - - B I Tl y I I I 'P & 24 Y L (- m o --- I 22 > T r 20 u I IB 16- J .WWÿ 4 WWg2 4 VVWg* 4 #6 VWg24'.V,,Vj V 6 TIME (HOURS) 5 5 TROMBE WALL DARK WALL AVC. TROMBE WALL - _ DB. TEMPERATURE WHITE WALL ______AVC. DB, TEMPERATURE -//? Fig. Measured surface temperature patterns of a shaded Trombe wall, an___unglazed dark wall and ---- a white ------wall (14). bl in regions with sunny hot summers it is desirable to ensure complete shading of the wall, not only from direct sun but also from radiation reflected from the ground. This system

Fig. (44)

I I

was developed by Horazio Barra in Italy [19] . The southern wall is insulated and is detailed as a thermosyphonic, air heating solar collector. The hot air emerging from the insulated collecting wall flows horizontally within channels, embedded inside a concrete ceiling, serving also as thermal storage. Part of the heat is stored in the concrete ceiling while the still warm air exits from the channels at the nonsun-facing, distant part of the building. The air thus warms the distant rooms first before flowing back through the building space to the inlets at the lower part of the sun-facing collecting wall. This assures an even temperature distribution throughout the whole house, which is better than the temperature distribution achievable with other passive solar systems. The Barra system can be applied

/a to multistory buildings, and even to buildings where the main rooms do not face the sun. When the front facade of a building is not facing the sun, it is possible to use the rear or side southern facades as the collecting wall because a major part of the solar heat is transferred first by convection to the northern side of the building. Thermal performance of this system depends largely on delicate natural convention currents. The moving air must come into contact with as much surface area as possible of the collecting wall and of the mass in the ceiling, without being slowed too much. These considerations should affect the detailing of the air channels. Sunspaces (also called conservatories or winter gardens) are intermediate usable environments between the exterior and the interior of the building. Being separated from the main spaces of the building, a much greater temperature swing (resulting from a large glazing area) may be acceptable within sunspaces, more than can be tolerated in nonisolated direct gainspaces. To contribute to the thermal comfort in the principle spaces and to the options of activities in the dwelling are in three ways [10,20].

1. They buffer the main spaces from extremes of exposure, thus reducing the potential

temperature fluctuation, glare, and the fading

of fabrics and furniture that may result from excessive indoor sunlight.

2. They increase the heat collection potential of .

61 a given facade by allowing a larger glazing area

than is practicable and desirable with direct gain.

3. The sunspace area itself can consitute an additional living space in the winter and the transitional seasons. With appropriate provision

for shading and ventilation in summer, such

spaces may be pleasant environments year round

in most climates.

Even during overcast winter days, when the sunspace temperature would probably be below the indoor comfort level and thus unable to provide positive heat to the building attached, the air temperature in the sunspace can be appreciably higher than the ambient air temperature.

Considering thermal characteristics and building design two types of sunspaces may be distinguished: - modified greenhouse, with a glazed inclined roof and sometimes also with inclined glazed walls. - sun porches, with a horizontal opaque insulated roof where the glazing is only vertical. Modified greenhouses: This form, with tilted or curved overhead glazing, maximizes the transmitted radiation since the roof receives the sun rays in late winter at a more optimal angle. The glazed roof of a modified greenhouse increases the total solar energy collecting area of a sunspace of a given height and width. A glazed roof is subjected to very high solar heat gain in summer. Therefore, greenhouses have larger temperature fluctuations, both in

winter and in summer than sun porches, and overheating in summer is more likely.

Sun porches: In this type of sunspace, the opaque insulated

roof reduces the large diurnal temperature swings caused by

the overhead glazing. The potential heat gain in winter is

lower than the case of a greenhouse but the possibilities

for control, and for year round use of the sunspace area,

increases greatly especially in hot regions . This type is

therefore advisable in regions with hot summers. /.£. Sunspace/building relationship: Sunspaces can have different relationshipsto the building proper, which affects the

thermal functional and architectural integration of the

building itself and the sunspace areas, sun as :

1. attached: outside the wall's line;

2. semienclosed: surrounded by rooms on two or

three sides;

3. internal: surrounded by the building on all sides (also called artia) . Attached sunspaces share only one wall with the rest of the building. They provide the greatest flexibility

for planning and construction, including solar retrofitting

of existing buildings. In regions with a favourable energy

balance they also allow the use of glazed end walls (eastern and western) , for maximum utilization of the morning and/or afternoon sun, although the risk of overheating in summer by

solar pentration through the end walls should not be

7/ overlooked .

Semienclosed sunspacews : In this arrangement the sun is indented into the building. Heat loss through the end walls is minimized without reducing the solar exposure, there by increasing the thermal efficiency of the sunspace .

Thus, for a given aixe of solar glazing, both the efficiency of collection and of heat transfer to the habitable rooms are enhanced, compared with an attached sunspace. Fully enclosed sunspace: type is sometimes referred to as an atrium, patio or even as a solar courtyard. As the sunspace is surrounded on all sides by rooms, the solar glazing has to be above the level of the roof to the roof to the sun facing side of the sunspace. This factor limits the glazing size but this limitation of lower heat gain potential, is compensated in part by the higher efficiency of heat distribution to the living spaces around the sunspace. This type has obvious applications in buildings with deep plan forms. Design options for the connecting wall. The types of connecting walls may be the following: - thermally conductive, massive wall. - internal Trombe wall {glazed massive wall) . - insulated wall with large connecting openings. - glazed and insulated wall. Thermally conductive, massive wall. This wall type may be built of any one of the conventional masonry materials. Such a wall is often also an integral part of the building's load bearing structure. Since this wall is not glazed, its

7ÿ surface temperature is significantly lower then that of a

Trombe wall under similar ambient conditions, and

consequently the conductive heat transfer to the interior

would be lower. Analysis of the heat flow from the sunspace

to the rooms in the Balcomb house < ) had demonstrated that most of the heat flow to the rooms is provided by convection. The mass walls has served

mainly as a heat storage for the sunspace itself, moderating

its temperature swing. Internal Trombe wall glazed massive

wall . By placing a layer of rigid transparent or translucent

plastic over a massive conducting wall, an internal Trombe

wall is created within the sunspace. While the solar energy

impinging on the wall surface is lower than in the case of an exposed Trombe wall . Insulated wall with large connecting

openings : As the conductive heat transfer across a mass wall

is small in comparison with the potential for convective heat transfer, the separating wall may be an insulated one, with large doors connecting the sunspace with the adjoining

rooms and providing convective heat transfer to the

building. Glazed and insulated wall . A layer of glazing may

be placed in front of an insulated connecting wall. Since an

insulated wall itself has no role in transmitting heat by

conductance, the principal purpose of this arrangement is to

supply air to the interior at a temperature that is higher

than that obtained with glazed conductive mass wall or with

an unglazed insulated one. The hot air may then be used for quick heating of adjacent or remote occupied spaces. Givoni

ll [10] has summarized and analyzed various studies in which

the performance of solar technologies in residential and nonresidential bu i1d i ngs , were moni tored [21,11,22,23,24,25,26,27]. Direct gain on a small scale,

providing solar energy to sun facing rooms through conventional windows during clear days and without thermal storage for the night hours, can be applied in any climate to any building with a sun facing facade, regardless of the number of stories. One possibility of solving the glare problem is to reflect the penetrating radiation toward the ceiling, by appropriate details of interior shading [28] . In lightweight buildings it appears that wider application of solar heating by direct gain depends on the development of new storage elements that can be an integral part of the building structure, such as wall and ceiling panels integrating phase change materials within the panel's composition [10,29].

The effect of heat loss on solar heating system describe by

Robert .T. Nash is :

Solar energy can only be collected and stored by making a rather substantial economic investment.

Consequently this energy, which is gained only with great technical and economic difficulty, should be utilized efficiently. It follows that the design of the structure should be such that this energy will not easily be lost through the shell of the building. However, relatively limited attention has been given to the role which.

74 structural energy loss plays in a solar heating system [30,31,32] . The structural heat loss coefficient, the collecting area of the solar collector, the incident solar flux and the external temperature are the dominant factors that determine the solar energy gained and the energy lost from a building. In

Fig. (45) a heat loss diagram is shown it has been assumed

m S'* ym V a m S« / / / i m •uL a m 1- I I" i -J—i 1 1 t MM maM «Sl fly.ys-. that thermal storage is sufficient so that an extremely small amount of the solar energy which is collected by the collector is lost. Of course the thermal storage capacity associated with a solar system might vary between nothing and 10 million Btu, the latter being of the order of the monthly heating requirement for a dwelling. In Fig. (45) a single mean value for the solar input is used, and a temperature of 70 °F inside the building is assumed. Several different value for the solar collecting area are shown, as are several structural heat loss characteristics. This diagram demonstrates in a general manner the relationship

75T between the mean solar energy gain and mean structural energy loss. To further illustrate the employment of this

type of diagram refer to Fig. (46) where actual data for

Oklahoma City are shown. In

.'V 0 --.-v / Z am.'**

O " — m M »H V* 1 I S - m r °o°

this case the physical collecting area is fixed at 600 ft , and it is assumed that the collector is oriented at an angle equal to the latitude + 15 with respect to the horizontal .

It has also been assumed that the thermal storage is sufficient so that any energy collected on a given day may be used during the ensuing night . Employing methods developed by Liu and Jordan [33,34], the solar energy gains and the associated mean temperatures are shown in Fig. (46) by a circled point for each day during January 1965, standard requires that the heat loss not exceed 830 Btu-hr-1 -°F-1 for a home with a floor space of 1500 ft [35] . In any economic activity the net return from purchasing and operating a piece of equipment may be defined as given below

[36,37] , This is the discounted return which occurs over the life of the equipment where p is the prevailing interest

16 rate and T Che useful life of the equipment.

Net discounted return e_pt = + fr Gross annual return. dt + Resale value at expiration .e~pt fr Gross annual expenses .e"pt dt Initial investment. '6/ The relationship given in eq No . ( ft ) applies in the case of a heating system used in a dwelling except that there is no gross annual return. In addition to dropping the gross monitory return from eq No. ( A ) , the resale value at the time of replacement has also been set to zero in eq No. ( A ) for simplicity. Net discounted return = -Initial investment in solar collection - initial investment in thermal storage - initial investment in auxiliary heating equipment - initial investment to control heat loss - fr Annual maintenance cost of equipment .e~pt dt - Loss coefficient /r (Annual needs-Solar supplied) . (unit auxiliary energy cost) .e"pC dt

It is appropriate to divide the costs into three separate parts. The first is the cost associated with the auxiliary heating equipment; the second is the cost associated with collecting solar energy and lossing energy through the shell of the structure, while the third component is the cost associated with storing thermal energy for the supplementary heating equipment.

17 Net discounted return - { I.I. (Auxiliary heating equipment). fr (Annual maintenance cost of auxiliary equipment) e“Pt dt

+ {- I.I. (Solar collection)

(Annual maintenance cost of solar collection) . e‘Pt dt 1.1. (Total structural energy loss) |. . . (Cj + - I.I. (Thermal storage) fr (Annual maintenance cost of thermal storage) . e'P** dt - /r (Annual cost of auxiliary energy) .e“Pt dt }. In this discussion no financial value has been associated with being comfortable, and in the direct economic sense of eqn ( C ) none can be. It is of interest however, to consider where protection from the weather fits into Maslow's hierarchy of man's needs [38].

In a technical sense heat has the same physiological qualities regardless of the sources or conversion techniques employed. Presumably this is a result of aesthetic considerations, or the satisfaction of one of Bentham's fourteen pleasures [39] , by combining initial costs and operational costs for each function we obtain the following. Net return = Total cost of auxiliary heating equipment . - Total cost of collecting solar energy - Total cost of losing energy through structure - Total cost of purchasing auxiliary energy - Total cost of storing collected solar energy Heating requirements vary significantly throughout the country. A measure of this total comfort heating requirement

in an area is the product of the number of degree days and

the number of residences.

The efficient transparent insolation materials (TIM) new opportunities are appearing in the fields of day lighting and passive solar space heating discussed by W.S. Wilke:

A new class of transparent insulation materials (TIM) has been developed recently [40,41] which could have the potential to increase solar energy utilization substantially. The high performance for thermal applications [42,43,44,45,46], can be extended when using this material or daylighting purposes at the same moment. Conventional windows with only glazing can be partly replaced by "daylighting windows" filled with TIM which possesses excellent thermal and optical properties Fig. (47) . The simulation program WANDSIM has been

Jl.

fe'i

V 4 4 'wTT*4 t-mm i 75 * hm *V JO. 1 i>M(UM« rf !«ÿ UMV« fM «kn<|d.i• N* MM >4k »#K>k4ik I n'j **.

developed. Fig. (48) shows the three different elements

8° no o br l!M 100- £ X §0- EE r g D / hr 5 rlr hr - 80- I'M rc I 40- £ : @3 is ; j> «- ? g K35 0- liS tn 1 Sfl -20 9 I?

100

TQ •0- •ÿV •1 p1 40- / V, A.A § Tw / v 40 / JL J J *E jo-

— To T;7 0- z - • •« -JO T T T T T < 12 20 < 12 20

1200 closed °pgn 1000- 1 j I roller blind £L eoo- ___ c 4r'“\ 5? sol t o 400- 4 » t \ 1 t /t -i I ! \ ST 40°- / » 5»i 1£ : 200- : i .ÿlillumi- . nonce) t z / T 1 o

-200 T T 4 12 20 « 12 20 February 17 th February 18th

IIMIWMI hmuteHon: « mm gun cover with 10 cm honaycorr* iiruciure matonry: 24 cm concrete {/l= 1.2 W/mK,.pe = 2000 kJ/m3K) roejcbjnd: opaque let M[h highly rqlleclkig (ST X), lowly R amllilng (13 X) coaling on bom tiOoi

9 Fig. 4. ( Ctmni. ) (b) Simulation results of the transparently insulated masonry

9t5> CA) glazing of wwxfcrw tjansparertty nsiiated masonary transparency insulated glass wall

- ir i fcr.viM • I i !i EE3! . ! i i I : "*or i Sir i r <ÿ h l Jfc_ ! i i ? ! I r \rzi t- fTlll ,1 J 'O' I <1 •» 'ii-TSrs\\ © 0 0 T © !l*)7> 0— 0 _ “ T. 'L na © - > ' -J 'v. - * If* *> .v ».« * ' '.O i *5. - >»'• *vv .1 *

— •ÿ•» yt"my -••v'1 __ ru: *'y*** j . : b' E53 ' h:ri*ir_ ! m r — - ~ SI -0 i ; . VJ..J.T«*• \ vo,j 1 a .J,.!. I l , Vari I i R »-L i o o **o 1 u i .1 !' *. *-v:,v3'-1 J A QJ 0 E3 i : n » " r CT X 4*) 3 T (ÿ» I * — > : *Cl> i *1 »: «« 1 2 ‘-- LlJ T A A IS _ * A A A A A 7 _ . i i T« ! Cl C*— T- V Hw i •f ; [3 * V Ej i i E| i jEJ i - ! i . i

n 1 C 3 ,? .Q .3 S >pc 0 1 * c..;T» J jvvv», ; 5 : -

¥ A T A • V**r q%* r-#«0 5» (VT.) . 5. ••'*5 t > :1 5. A. •D »3 ("*))• 5«.- Joy w*'v>* "#CI — J ' ii%n ;9W»» ir*j’.; » * *? V#nv5lr 73 r* 3lv- 2': Fig. The tha\: systems lo compare and lheir modelling as elecI nonl network.

\ i 1 i for daylighting and/or solar heating which can be simulated by the program WANDS IM. The program WANDS IM uses

the finite difference method [47] to solve the partial

differential equation of heat conduction, with unsteady

boundary conditions, for an arbitrary combination of

transparent or opaque layers with or without thermal

capacity. The solar radiation and ambient temperature are obtained from the weather data, inside air temperature from a predefined profile. To calculate convection in air gaps the formula given by Hollands et al . in [49] is implemented. For a proper simulation of transparent insulation material

(TIM)., two points have been taken into account: - the temperature dependent thermal conductivity (Linear fit) of TIM. - the operation of a roller blind system to reduce light transmission and heat loses.

Some remarks on the controlling of the roller blind system may follow here.

The roller blind closes under the following conditions:

1. The absorber temperature T exceeds 80 C (irrelevant for window glazing) . 2. The solar radiation qSQl is 20 W/m2 (nighttime) in the water. 3. The solar radiation

Si To is continously calculated to distinguish between summer and winter. If T24h < c> winter control mode is used, and if T24h > c> summer control mode is used. The thermal behaviour and daylighting performance for. a selected case of each system shown in Fig. (49) (a) - ( c ) . The

a* Modelling and simulation of dements for solar healing and daylighting

no P too- £ eo _ % SO¬ IL <0- I 10 - l 0 - ~20

100

00-

z? •0' s 5 § 40-

1200 closed °p*n j 1000- i / ¥ \-Troller S, aoo- ___ blind 1 \ -5 t I .5 ,0°- ( illuminoncel i t/cy 400- W\ 1£ 200- 1 l r r 0

-200 T T T T T T 4 12 20 4 12 20 Februory 17th February 18th

amy doubts faring with 4 rrm standard panes and SO mm air gap iol»f bind: semitransparent lot rath highly rallscilng (60 X), lowly fi omitting (SO %) cooing on outer side

Fig. 45(a) Simulation results of the glazinp

83 Modelling and siinulalion of elements Tor solar healing and d.iyliglitine

120 100 x N u - Si ss MfxIn t- 10- u I:ÿ R~ s 'x ; T*K>\ 'FT 3 ao - as fit; X 8 40- K- IS R O. :r. c- 20 - R- 1 " o- / ;rr. r £ £ -20 J 4r M 1

100

eo-

77 40' To /_ / Tw V. -3 o 40- / -/ ./ 1 20- To r „ Ti 0- / ...... - -20 T i i 4 12 20 i 12 20

1200- closed 1 °P*° WOO- / V' J J roller a, aoo- ___ blind % t \ I .5 ao°- » « I / 400- I I #/Y \ J £ I 200- .• o » L. "••4,.. I I 44...., sex 7 •—I 0 E [illuminance) -200 T T T T 4 12 20 4 12 20

February 17 February 18th

lynipan m jniufrUon: 4 mm glut covor with 10 cm N»«rycomb aimctur* glut w*I; 24 cm wWtt glut (A* 1.2 W/mK,pc* 2000 kJ/mÿK, f « 0.07 cm"') toi»r bind: optqu* fo* vdlh Nghty rtfWclrvg (07 X), lowly ft #m!ling (13 %) coating on both j*dt»

I'IR. 4$( r 'twitl. ) (c) Simulation rr*ulis of iln* inimparcnlly insulalcd wait i

9H. choosen example is a double glazing of standard panes with a semitransparent roller blind operating in between

Fig. (50) . The light passing the closed roller blind

IS'/S':-

...... >W1.

is of diffuse character and suitable for most activities. Detailed data of the system can be taken from Fig. (49) . The illuminance E directly behind the inner pane is very high, however the light has mainly beam character and will therefore cause marked shading. The energy flux q increases strongly during the day but drops to negative values (heat losses) during the night. In spring and fall it very often occurs that heat surplus in the daytime results in opened window and a loss of the heat which could have been stored for night use. For the simulation, a usual wall of concrete is selected with polycarbonate honeycomb TIM. The roller blind placed in the air gap between the TIM and the absorber is opaque and of very low IR-emissivity , which reduces heat losses at night and avoids overheating in the summer. The material date is given in Fig. (49) (b) . The heat capacity of the wall causes a time-delayed and damped delivery of the absorbed solar energy to the inside. The time delay is

£5" dependent on the term D2/a, where a is the thermal

diffusivity and D the wall thickness.

The example differs from the case of transparently

instead masonry only in the fact that the wall is not opaque

but translucent. Al thermal material data is identical to

the previous example and once again summed up in Fig. (49) (c)

The sunlight is not absorbed at a surface but partially

throughout the material, therefore acting as an inner heat source. The extinction law. dl = - Iedx where I is the intensity, forms the base for the calculation

and is symbolized in the electrical network by current

amplifiers for qsoi . The illuminance E at the inside of the wall

consists of diffuse light and is substantially lower than

the system with only glazing. If the solar efficiency ngQÿ

is defined as the contribution of qsol to the energy flux , the equation can be written in the form.

Qi = nsol<3sol “ V The solar efficiency nsol is plotted versus D in Fig. (51) .

% •i a* M-

M J “I •• kA t

/ \ T T T T T T T T T

fimarr n

J fij. .

&6 Fig. (52) shows the insolation on a vertical south Modelling and simulation of elements Tor solar heating and daylighling uo diffusa totol insolotion: 778.37 kWtyhn' “1 i-~ ZZt baom f= « 3 «o- e i 6 40- 20- iiHHy»iiMMai 0*

40 onergy IOSMS 93.1 mkVtVn* 20- 3 r „ r=-i 3 n<£> oo rsi

f* -20- i

-40 R " gj V "MIWWII"~ cn ro s -•0- (b) glazing energy gains 289.4 kwym* -10- 3BlSll$3BiSi§ 40 energy losses 0.4 kWfyfn1 20-

O

? " ~ f -40- M 204 a: . CM coCO

-•0 (c) TIM masonry •nergy gains 223.7 kwym' -B0- I B I 1 1 i i I §i S | g Fig. Solar insolation on vertical, south-facing surface and energy balances(a) for glazing(h ) transparently insulated masonry (c) and transparently insulated glass wall (d).

Q7 Modelling and simulation of elements for solar healing and daylighting

40 energy losses 0.5 kWhvW •T"* 20'

d o o- S’ S -20- -!ÿ?? s . s 5 9 9 9 -40-

-•0- (d) TIM glass wall energy gains 231.7 kWlyW .to- i § i % 1 3 a 3 Si § ? 8 facing surface and bar charts for each case. The inside air temperature T has been held constant at 2 0 C. Energy fluxes q into the room have been integrated as negative energy quantums (Since they off set other heat losses of the room) on the side labelled "energy gains". Energy fluxes to the outside have been integrated as positive energy quantum (because they required heating energy) . The heat gain of each system can be properly predicted by WANDSIM, but not the electricity saving as a result of the reduced use of artificial light.

Similarly the Solar-Assisted Heat Pump Systems are describe by K . Kaygusuz , 6: Due to rapidly rising oil and natural gas prices

(in Turkey, natural gas and oil are imported and oil price is 28 $ /barrel), alternate energy sources such as solar energy are receiving greater attention for heating, cooling, drying and power generation applications; the use of heat pumps for residential, commercial, and industrial heating applications. In order to improve the heat pump COP and

as displace the fossil energy resource, the idea of combining

the heat pump and solar energy in mutually beneficial ways

has been proposed and developed in several previous studies

150,51,52,53,54] . Solar heating of buildings and food drying

(for example in our regions nuts, com, beans and tea)

requires the accumulation and storage of solar energy to

provide heating for nights and for cloudy days, since it is

available on clear and partly cloudy days. Some investigations on the drying of grains are reviewed in [55] . Since early in the history of mankind, use of solar energy

in drying agricultural products has been extensively

practiced in most parts of the world, especially in the form

of the open sun drying. However, open sun drying results in

inferior quality because of contamination by dirt and insects, degradation of the products, wastage, etc., and is a slow process. The solar drying system considered here has a unique feature in that the air flows in a semiclosed loop and that an energy storage unit is provided to enhance the versatility of such a system. The storage unit is a latent- heat type consisting of a tank filled with encapsulated PCM packages through which hot water steadily flows. The solar assisted heat pump system linked to a phase change storage tank described here is at Trabzon,

Turkey. It was intended for the drying of granular products

(for example nuts, corn, beans) and air conditioning of the buildings in the Black Sea region of Turkey. A schematic

<3? overview of Che system is given in Fig. (53) .

£ £ l ,CMvr«i»l

tvtirt* iviponioi 4. Alr*»Mir« U *. TFMIIMI n«rr*vio| b. ri«s«i itMMt 1. Dr v*r . *«!• . b« I >M>14 *•!»ÿ >• » ic. r » l»4|» II. NiMBMil CKZI |], Tfc*n«M •«.'!* aft* II l>. l».r»v f£1 ‘ TL 14. CulUntr 1 1$. 'li >n*» i* i ! fr ® it. Chtct v«l»* i_ __ f? 17. n*« MI«I il. *n MI1« rii» IV. *«ri»»H»p *•>« «M -C-O-Cj-O-O- 70. lir«B»l»n f|. IU(MI|f ¥*!*• -A ii, ii :i, 4 I 74. *ÿ!*• In 10 2). D«<» lo|tr iS: U 17, 1 If .'I. Inlaaiali'r it 4 I_& Js»ilu—*0*“*- * * • - 53 lyiiem. — Fig. A sehtmaiic rcpmcntalion of Ihe

Solar collectors were constructed by modifying flat

plate, water cooled collectors. The compressor used for the

experiment was a hermetric type. It was driven by a 2 hp (1490 watt) electrical motor.The heat pump can use air and water as a heat source. Used 1500 kg calcium chloride hexahydrate for solar energy storage because the commercial ca d2 . 6H20 is cheaper and it has a better thermal stability than the other salt hydrates [56,57,58] . The heat is absorbed during the melting of the PCM and retrieved

during the solidification of the PCM at (nearly) constant

temperature. The heat storage tank was linked to the heat

pump by means of a chiller for use as a heat source. The

pressure, temperatures, and flow rate of the refrigerant (R-

22) and water were measured at the locations shown in . s' Fig. (53) . The ambient air temperature, relative humidity, incident solar insolation, and eighteen surface temperatures on each of the eighteen solar collectors were measured.

Temperatures were measured with a manometer. A Kipp-Zones solarimeter, mounted in the vertical plane of the solar collectors, was used to measure the solar insulation. Water flow rate was measured by means of two flowmeters. The relative humidity was measured by means of a humidity meter.

An automatic data logging system was used for data acquisition. Solar-assisted heat pumps can work in three forms. The three combined systems are the series system in which the solar storage is used as the source for the heat pump, the parallel system in which ambient air is used as the source depending on which source yields the lowest work input. The heat pump system has five modes of operation. - Mode 1, parallel system (nonstorage) - Mode 2, series system (nonstorage) - Mode 3, series system (with storage) - Mode 4, dual system (nonstorage) - Mode 5, dual system (with storage) We have analyzed only mode 1, mode 2 , and mode 3 during the experiments. f The collector efficiency rjcoll is defined as, = Useful energy collected energy incident in the plan of the collectors mCp_ITwo ——wi-ÿ— IA c

<3/ where Ac is the collector area (m2) ; I is the solar flux available in the plane of the collector (W/m2,-m is the water

flow rate

—out hin- 1 condenser

—' ) (6) hin compressor . . .

COPsys (7)

w total

(9) COPsys =— ----• • • • wtotal Where Q con and Q exc are heat loads of the condenser and exchanger respectively/ W is electrical work input to the compressor, pump, and fans.

Fig. (54) shows the collector efficiency (n/col) as

luo

n IQ

• to.

!: * lytiia wiili irdri|ij4 July |tfO 10 lyatfi BOA ,2* July ItW i • l/itM Mil July ItIO 5 " 10

i.JO JO. JO X) II. D.00 |4. )0 Ik.00 17. JO Tlw of Uf ----—n-mm 100 90 *

30

N 70

60 >>u

H 50 O A A *ÿ4 •44 40 II V4 o 30 Series system with storage, 1 August 1990 u Series system non storage , 3 August 1990 _4I f-1 20 Parallel system non storage, 2 August 1990 o • cj 10

0 I + I i l i I 1 1 1 8 10 12 14 16 18 20 Time of day

Fig. efficiency versus lime of day for three systems.

Solar-assisted heat pump systems and energy storage .1X7 900 scries sys.witli storage ,24 July storage, 25 July CVJ 800 sys.non 4 series sys.non storage, 27 July 2. 700 c o 600 4-* 2 -a 500 2 u 10 400 <8 300

200

T 100

0 x x 8.30 10.00 12.00 14.00 16.00 18.00 20.0 se¬ Time of day nt. Solar radiation versus lime of day. °l2> Figures(S"j; sV, 57) show the variation of experimentally

measured values of solar radiation (I) as a function of time

for three different systems.

900 -tp 800 700

600 *v 500

5 400 »—< 300 'iu atorago.l August 1990 U 200 m Series ays. wich + Series sys. noii storage , 3 August 1990 100 •Parallel ays.non storage, 2 August 1990

0 X 18 C 10 12 14 1 6 Time of day SI- Fig. Solar radiation /(W/m1) vcnuj time of day.

Also G.O.G.LoF reviewed the design of optimized systems for residential heating and cooling as:

One of the methods for cooling buildings with solar energy is by use of an absorption refrigeration unit supplied with heated fluid from a solar collector. A system which has been successfully tested comprises a lithium bromide-water absorption cooler provided with hot water from a glass-covered solar water heater. In order that solar air conditioning can be available at the lowest cost, it is essential that the solar collector be utilized both for

Errs

T ~'*zm i 'IT"S' I

*1

hy-5* The solar collector, heat storage unit, hot water heater, auxiliary heating unit, and the facilities for heat distribution to the house are essentially as employed in the previous heating study. For cooling, the operating conditions or collector, storage, and auxiliary are modified, and absorption refrigeration machine of the lithium bromide-water type is added to the system. The refrigeration unit has a nominal cooling capacity of 10.55 kw (36000 Btu per house, equivalent to three "tons of cooling"), with a 0.6 coefficient of performance, i.e., a heat input rate of 17.58 kw) . The hourly demands for space heating and water heating were computed as described in earlier papers [59,60). Building requiring 0.33 and 0.55 kilowatts per degree (C) atmospheric temperature below 18°C were selected. Spade heating loads are therefore: H = 0.33 (18 - t ) and H = 0.55 (18 - t ) for the small house and large house, respectively. Hot water was assumed to be required at rates equivalent to 0.183 and 0.305 kw respectively. Cooling loads were determined by summing sensible and latent heat generation in the buildings, and sensible and latent heat transferred into the building by conduction and air infiltration. The cooling load was expressed as a function of ambient temperature and humidity in the following equation: C (kW) = v [3.55 x 104 (ta - 25)] + 0.818 (ha 0.0096) . . . (10) + 0 . 682w + gs + ua (tQ 25) s

It where C = hourly cooling demand, kw v = cubic meters of air admitted/hr ta = ambient temperature °C ha = humidity of ambient air, g water/g air w = water vaporized in house, kq/hr g, = total sensible heat generation rte, kw

ua =* effective heat transfer coefficient x area of windows and north walls, kW/°C temperature difference. s = heat conduction rate through roaf and south, east west walls and solar transmission through windowsÿ kW/c:- Since the value of the terms depends on solar radiation, time of day, etc., a final equation was obtained by substituting for s, an expression containing various terms involving radiation, building dimensions, and solar angles. Terms in the above equation other than ta and ha were parameterized at two levels, one for the small house and one for the large house. Values chosen were v = 141.6 and 566.4, w = 0.4535 and 1.361, g = 0.586 + Is and 1.465 + Is were [Is = heat loss rate from storge tank, equal to 21.12x10 (t - 25) and 158x10 (t -25; t being storage temperature], ua = 0.119 and 0.172 roof areas are 112 m and 232 m, west wall areas are 23.2 m and 30.7 m . and south wall areas are 30.2m. and

44.6 m. With these equation for the house heating, water.

kW heat rate per kW cooling rate, substitution of hourly

values of atmospheric temperature and humidity provided the

hourly heat requirements of the buildings of chosen design.

The mathematical model and an outline of the computation

procedure for the heating system operation and analysis are

to be published [61] . Addition of the cooling function to

the solar heating system previously analysed was accomplished without material modification in the equations

for solar collector performance and heat storage

performance. The withdrawal of heat from storage for cooling was assumed to occur only when storage temperature is at least 82 °C (170 F) . Hot water from storage passes through the auxiliary heater where sufficient heat is added to bring the water to 93 C (180 F) . No auxiliary heat is supplied if the storage temperature is 93 C or higher. The cooling

demand in a particular hour, computed as previously

described is then met by operation of the cooling unit for

a sufficient portion of the hour with heat from storage,

with or without auxiliary, dependent on storage temperature.

Water returns from the cooling unit 5 C cooler than

supplied to it. If storage temperature is below 82 C the

storage tank is by passed, 93 C water from auxiliary being

supplied to the air conditioner and returned at 82 C directly to the auxiliary heater. Annual costs of the solar

heating and cooling equipment were determined by methods

outlined in references [59,60], supplemented by analyzing a.

96 cooling equipment investment surcharge of 51000 to cover the additional cost of an absorption system (with water cooling tower) over that of a conventional compression unit.

Selected results of the solar heating and cooling analysis are presented in Fig. (59-64) .The graphs shows the costs of solar heat for the purpose. •* 4 * 1 ? * " ; -• 4 I ,v r M 4 4 I % r’ * « *» I ** >ÿ t n »W4 fa f l- V 1 * I «* y «• •» 7 « r ** * t !» • ,*» f i '* w «i \ •i ft 4. • ' #• V. t* * •« » Mv« I ,0.?U7.> "t M -xn V* x* i 9 II k% l'*e# •* %• W«Wt « r*- \ •< 1 • r< 1 C «I • a* a • 4 I !•««•»• ti’i'iOKl •• M t-'llfcl.'l «, i n («•ÿ f * X <4 M 1440 »- IM * *a m I *H>ÿ4»/ »*r >41 Ipt* MU •*« I I •• *V iO k __ 4 . * II ft' ft* (•»H 4-44 '•* I S?

I1 v

41 - 4 > «

M * » i* M& r »r Jv V fV • !• «• 1 \ 4 a «’J a i m . 1 » V- 4* 4 - ’ " <••*•** 4—I4-I »» «»•••• »l ' »M I v t» CV LH ••* 4.«ia» V it » r*#» »ÿ » r a • • * • « a -a- r« - « • « • ••- - -rti' • /Cvav I » ft .ÿ• »• M* • *> r*v » |i<> > >*-» • . . •S I* * »1 | 41-*' I f! -'l ( r t *•»! •, IP I -41 I I n * . l»»*l f. •ÿ<)! l|KI •*ÿÿ1 » *• • » r»i >M / C • ft o . a •r l

i * rty 12.

IK iHi< i/.J >| «

y '* , . • • 4 4.1 .•f • • ' I ' i -4 \ « • >

V *4 v> .- I I )’ _.v •

1* V V a » » a 4 •• 'i it.- * a •~.*i 1 *4 \ /( M ij <: l M (vMH •• v I — ; ft 4 ft Cftfta i • b — 41 — A i 4r4i«-l »ÿ a#4la V ftaft !•*•»i ir a •— •r.|# faf !' !•-*,». T* ¥ ,-\y 'lift - - •I t ft* lr-nl ftt X *W*~4 ftf 4 f-s I** »w •- an • ' n* I•Vft* a- 0 rV * |M« 11 V" • 4 / •’ill »n* • I la*1»• tl1* » M4IPM 4f Vf at I44t'llal *4 ’• •" >•* -»!•«< l«ta>.M.i*u ft i . t . aft / 4 L ft >> W M Kr 44 l> ft* L — ft •* Hit CtrPI •a C3 >« Also shown are the relationship between costs, collector tilt, and number of glass cover. Each of these four design variable is seen to affect cost and to have an optimum value at which the solar energy cost is a minimum. Collector area has a large influence on solar heat costs, where as collector tilt within the range studied has a minor effect.

Further Takeo Saitoh in developing energy independent house combining solar , thermal , and sky radiation energies proposes system has two operational modes: (i) a longterm thermal energy storage (TES) mode extending from September to early

December, in which solar energy is collected and stored in an underground water tank for the space heating and domestic hot water (DHW) needs of from early December to late March,- and (ii) a long-term cool storage mode extending from April to mid-June, in which the water of the same tank is cooled by employing sky radiation cooling devices.

It had been argued that utilization of sky radiation cooling in the Japanese climate is almost impossible due to its high relative humidity (80% 90%) in most areas in summer.

Long-term thermal energy storage systems employing the underground reservoirs have been constructed in the United

States, Canada, Sweden [62] and Japan. A schematic of a natural energy autonomous house (NEAH) is shown in Fig. 65) .

Principal specifications appear, The s*>’*“»* »“ • /|\

[ 1 1 1 1 j r> ..... 1 J i i a?**1 • 'f

f s3nw- > V r;j.fcs 101 NEAH features an underground water tank, a solar collector, a sky radiator and tank for rainwater storage. Fig. (66) shows an experimental solar house at

23r,•vW %mm> C«Hi >w ' "'W

t* U» a $ -ffj

Tohoku University, Located in Sendai, Japan (latitude and longitude 38 16' North and 140 54' East, respectively) . The average solar energy received on a horizontal surface in January in Sendai is 7200 kJ/m /day. The dimensions of the underground water reservior are 4,3 by 4,3 by 3.1 m in depth. The reservior is made of poured concrete (thickness

0.2-0.3.m) and contains 37000 liters of water. Copper- constantan thermocouples are set up at more than 60 points in the wall, water and soil in order to measure the temperature and the heat fluxes around the reservior. A detailed description of the under-ground reservior is given in Fig. (67) . The solar collector

r-** •.y o* ft* ’•»' 'MU [ * rvp ;r j;7 •"4ill~rT- r f-r¥f HJ

..rrc »* l > >/H jif I «i ilifch. ».t. ' V,.

/OJL (manufactured by Yazaki Corporation Ltd., and having an area

of 47 m values, an intercept F of 0.815 and an overall coefficient of heat loss U of 5 . 0 W/m K) is installed on the top of the laboratory house with a tilt angle of 60

from the horizontal. A large tilt angle was selected to

increase the collector efficiency in winter and to permit

easy snow removal from the collector surface. The collector

panels face due south and the water of the reservoir is

circulated to them by the pump. To prevent freezing in

winter, the water in the collectors and pipes are

automatically drained by magnetic valves. The sky radiators

used in the experiment are an uncovered stainless-steel

panel pained black (area: 17.2 m ), and placed due north

with a tilt angle of 50 . The circulating pump for the sky

radiator loop was automatically operated just like the solar collector. The flow rate was fixed to be 1.83xl0"4 m3/s (11 liters/min) which was chosen to give the maximum cooling

efficiency. The inner walls of the reservoir above water

level are insulated by 0.05 m thick Styrofoam to decrease

the heat losses. The inner walls under the water level and at the bottom are insulated by vinylchloride pipes (0.11 m

O.D) partially packed with glass wool. Fig. (68)

30 A\ % o40 A; 'V •30 V

M/4 Mr OCT MOV D*C JAM HI nmt <•«»

FMUJ.3 gives the long-term variation of the average water temperature of the underground TES reservoir. Space heating was undertaken from 1 December 1982. It can be seen from the figure that the water temperature decreased before space heating was started. This was caused by a decline of solar insulation during November, and is in agreement with the result of a simulation [63] . The heat-loss distributions along the reservoir walls (i.e. North, South, East and West) and the corresponding water temperature profiles in October are plotted in Fig. (69) . It is seen that the heat loss

H/m* -4x°— VJM-S *c 10 30 40 SO

»I'K t-itfUa a !

® -t - MIOO*

1xÿ1 '**"*** V9- from the upper surface and from the vicinity of the water level is considerable; the thickness of insulation near the water level is relatively thin and the water temperature is higher in the upper postion of the reservoir. Fig. (70)

C-J --1 2 - -- . .«'r. . * ,0 -

a JW L* |r.»A « tr r<* f .'fc'iM N'-cr* •• rwm»< *T70 • toll donates the relationship between the heat loss Q and the difference between the average water temperature and the

soil temperature 2m underground. The dots represent the experimental data and the solid line designates the least square fit to the experimental data. A close relationship

between the two is observed and seen to be independent of

the seasonal variation of the data. This relationship can be expressed by the following equation: QL = 4.O8A0 +5.35 (MJ/day) where A0 is the temperature difference between reservoir and soil . The experimental data using the real sky radiator are shown in Fig. (71) for the period from 20 March 20 ro to V

:u l IO V F->7/ ?•

N|Ml I.+ < >|vintNJ +M July 1984. It took only two weeks to decrease the water temperature of the TESR below 5 C. The reason that the temperature rise rate from late-April to mid-June is relatively large is again the fact that the insulation thickness is very thin. Typical time sequence data for sky radiation cooling are recorded in Fig. (72) . The figure plots

10 '•ÿ4 imtui ir **> V'lt « io y 5* • T- » - • tNLLF T(U>

4 0 OuTKT TEMP.

i -a

4/iJ 4/14 4/14 lOOO ooo 400 BIT( , nm r* f hHMHli «ÿ fy toS the inlet and outlet water temperature of the sky radiator

operated for one clear night. The cooling due to sky

radiation occurs mainly in April and May so that the water

temperature decreases in this period. The space cooling

becomes almost impossible during June to mid-July partly

because the temperature difference between the ambient and

the reservoir is large, and partly because the rainy season prevails over most of Japan. Fig. (73) shows schematically a basic thermal solar

a,Jlx r,Tiy

heating and cooling system for a residence. This basic

system, for which design data were available [64] , served as

a standard of comparison for developing a viable photo¬

chemical system. The thermal design utilizes a conventional

forced-air unit with a hot-water, heating coil and an absorption-type air conditioner. The solar radiation is

converted to thermal energy (sensible heat) in the solar collector where water or water-glycol is circulated through a flat-plate heat exchanger. This heated water is then

returned to an insulated storage tank. To heat or cool the

(Ofr house, hot water from the storage tank is circulated either

to the heating coil or the absorption unit. A solar energy system is generally designed to supply from about 50 to 80% of the thermal energy requirements for winter heating, summer cooling and hot water. The optimum collector size and storage volume depends upon many variables, including the costs of the components, local fuel and electricity prices, house design and geographic locations. The results of two such computer studies (64,65) were incorporated into this systems analysis. A nonmoving, flat-plate collector is the lowest cost type of collector for use in residential, commercial and industrial cooling systems. These collectors typically convert about 25% of the total solar radiation available on a clear day to useful thermal energy, with a maximum noontime efficiency of about 40%. As is well known, a flat-plate collector utilizes not only the direct solar radiation which falls on it, but also the diffuse

(scattered) radiation. The diffuse component often amounts to 15-20% of the direct radiation on clear days. Generally, the collector is mounted in a tilted position, facing southward, to balance the energy inputs relative to sun angle between winter heating and summer cooling.

Fig. (74) shows the predicted daily variation in the

5

r ! > • :::MH i lo1 ~kU solar radiation impinging on a tilted flat-plate collector

[66] and the amount of energy transmitted through two panes of double-strength glass [67] . These calculations were made for collector located at 32 north latitude (representing

Albuquerque, New Mexico) and tilted southward at 30 above the horizontal , assuming clear sky conditions. A major advantage of a photochemical solar energy storage system over a thermal system is that in principle the chemical system can operate all day, every day at constant efficiency, even on cloudy or heavily overcast days, there will be sufficient light intensity to operate a photochemical system to some extent. If a chemical material can be synthesized which has an overall conversion efficiency 25%, the photochemical system could collect as much energy as a thermal system can on a clear day. On cloudy days, the photochemical system could still collect

25% of the available solar flux, whereas the efficiency of a thermal system would decline appreciably as described above. It is further envisioned that the collector for a photochemical system would be simple and less expensive than that for a thermal system. Fig. (75) shows the predicted

/'v 7/ (f At-- - l \ . \ [i i V ; V; -V V /y 17 "rJ-

|0? _Q. average monthly energy requirements of a typical 1800 ft (167m) house. Qh represents the heating load, Qc the cooling load, Qwe the water heating load supplied by the collector

Qws the water heating load supplied by the service hot water auxiliary heater, Qaux the heat supplied by the main auxiliary heater, Qtot the total energy required, and Qavg is the yearly average of the Qtot curve. It is fairly typical of more northern climates (66,68). Fig. (76) shows

JOO Vttiplt _ Rooge 80

80 UI'J

lu l 40

20

400 700 1000 3000 Mbvtlenglh , nonomttcr a

Fi£ . Solar energy spedrum.

the percent energy existing in the solar spectrum as a function of wavelength, based on the spectral distribution. On mid-summer day at noon f 69 ] , a "blackened" heat exchanger in a thermal collector will absorb most of the solar energy over the entire spectrum, whereas a photochemical collector might be expected to utilize only the shorter wavelengths.

The curve shows the importance of developing a photochemical fluid which will be activated by wave-length

/c

1| T«»*l H

& ic—

F'1-77. which indicate comparisons between a thermal system using hot water storage and a photochemical storage system operating at room temperature. The thermal system has a flat-plate collector consisting of two glass covers, an aluminum tube-in-sheet heat exchanger painted flat black, and insulation. The overall thermal efficiency of the thermal system's solar collector would be about 25% on clear days when two untreated glass covers are used. This type of treatment was apparently accomplished by RCA some years ago [70,71] . The hot water storage tank was optimally sized during the computer studies, as was the collector and other parts of the system, to provide the least annual cost per unit of solar heat delivered to the heating and cooling system [64] . In most climates a water-glycol loop will be needed for the collector circuit in winter. The cost of the collector for a photochemical system is kept to a minimum when only chemical energy is collected, rather than thermal plus chemical energy. If one attempts to collect thermal energy also, the collector design and cost become

HO compariable to the thermal system's collector with a glass covered heat exchanger replacing the aluminum unit. The simplest collector design envisioned for a chemical system consists of two panes of glass between which the photochemical fluid is circulated. The overall design also allows for room-temperature storage of the chemical energy.

To prevent excessive heat losses from the collector during the winter months, a small counterflow heat exchanger can be used between the collector and the storage tank to preheat the returning fluid with the out-going fluid. /\ comparison of similar thermal and photochemical solar energy storage systems on the basis of

(a) equal total present -value cost of collector plus storage, and (b) for equal quantities of energy collected and stored. On cloudy days the efficiency of the chemical system will remain constant, whereas that of the thermal system will be less. Fig. (78) is a plot of the

J- ! r w j •* w\ '44--.:;;;*

Ej.}3 ,

III chemical energy and efficiency required of a photochemical system to match the winter operation of a hot water thermal system points for these curves were taken from Table (1) The area to the upper right of these curves represents conditions where a photochemical system will have advantages of lower cost or better performance. It should be remembered, however, that the actual performance of a chemical system will be somewhat better than these break even curves indicate, because of better cloudy day performance and greater summer energy storage.

A method of estimating the long-term thermal performance of solar space and domestic water heating system which use liquids as the energy transfer and storage mediums is available [72,73,74] . The correlation, presented in both analytic and graphical form, is referred to as an "f-chart".

The solar air heating system chosen for investigation is shown schematically in Fig. (79) . Air heating systems of this

r f •4*110 H»U jtfei ' 2=irrar X-J oel 7M»*J [

i W—«

configuration have been installed in the Denver Solar House

[75] in CSU Solar House II [76] and in other solar houses.

This system has three modes of operating. Mode 1 occurs when solar energy is available for collection and thee is a space heating load. Then, room temperature air is drawn through the solar collectors, heat, and returned to the building.

Mode 2 occurs when solar energy is available for collection at times when there is no space heating load. Air from the bottom of the packed bed is drawn through the solar collectors, heated, and returned to the top of the storage unit. The hot air moving down through the bed heats the pebbles resulting in sensible heat storage. Mode 3 occurs when no solar energy can be collected but there is a space heating load. Hot air is drawn from the top of the packed bed into the house and room temperature air is returned to the bottom of the bed. In modes 1 and 3, auxiliary energy from a conventional furnace may supplement the solar contribution. Energy required for domestic hot water is provided in some systems by heat exchange from the hot air entering of exiting the collector (shown exiting in Fig. (79) to a small domestic water preheat tank. Models used in the computer simulations for the solar collector, the space and water heating loads, and the auxiliary energy supply are identical to those developed for the liquid-based solar heating system described in reference [72,73,74] . The mode of operation of the solar air heating system in Fig. (79) is determined by the position of the motorized dampers. The collector operation is controlled by an on-off differential controller monitoring the temperatures of the air in the collector outlet manifold, TQ , and in the bottom of the

ttl pebble bed, TN , as indicated in equ TQ - TN > , Collector is operating TQ - TN < 0T2 , Collector is off. AT-ÿ and AT2 are controller deadbands ideally chosen so that the energy collected is at least equivalent to the energy required to operate the blower. Both and T2 have been chooses to be 5°C in the examples noted here.

Dampers B and C are controlled by the building thermostat.

Whenever the building needs heat, the dampers are in the positions indicated by the dotted lines in Fig. (79) .

Otherwise, their positions are those indicated by the solid lines. An alternative method of modeling system performance, suitable for long-term simulations, is not to follow the system mode changes exactly, but rather to assume that during any time period, the system operates in whatever modes necessary to maintain the building temperature at the desired level . This method of calculating system performance allows the simulation to use time steps on the order of an hour without a sacrifice in the accuracy of the calculated long- tern system performance. The temperatures of the air and the packing material in the storage unit can be described as a function of axial position in the bed and time by a set of two partial differential equations [76,77] . These equations can be solved by numerical method. A simpler model of packed bed thermal storage, useful for long-term simulations of solar air hating systems, has been developed by Hughes, Klein and Close [77] . In manner idential to that used to uc/ develop the f-chart for liquid-based solar heating systems,

the fraction, f, of the monthly total heating load supplied

by solar energy calculated by the cimulation model has been

correlated to the dimensionless groups X and Y. X = AFR_LJL_iTref.ÿjral L Y = AFR (T«)S L where A is the collector plate area; Tref is a reference temperature chose to be 100°C; Ta is the monthly average ambient temperature; S is the monthly total radiation incident on the collector surface (per unit area) . The collector design parameters FR, UL and (r«)n can be determined for a specified collector in the manner described in Dufie and Beckman [78] or from collctor test results such a those presented by Vermon and Simon [79] . A graphical representation of equ appears in Fig. (80)

f = 1.040Y 0.065 X •• 0.159Y + 0.00187 X 0.0095 Y

for, 0< Y < 3.0

0< X < 18.0 and 0< f < 1 Y > 0.07X.

uS The collector overall efficiency factor, FR which appears in the dimensionless groups X and Y is a function of

the collector fluid capacitance rate as discussed in Duffie and Beckman [78] . Aside from affecting the value of FR , a change in capacitance rate affects the thermal

stratification in the packed bed. An increase in air flow

rate tends to improve system performance by increasing the value of FR but it also tends to decrease performance somewhat by reducing the degree of thermal stratification in

the packed bed .

Comparison of the f-charts for the liquid and air

systems indicate that for the same values of X and Y, the

air system outperforms the liquid system, particularly for

systems designed to supply a large fraction of the heating

load. There are several reasons for the behavior. First, the average collector fluid inlet temperature is lower for the air system. Second, the thermal stratification is ordinarily maintained at a higher level in pebble beds than in water

tanks primarily because of the smaller fluid capacitance

rate normally used in air heaters. A third reasons is that a heat exchanger between the storage unit and the heating

load is not required in an air heating system and thus the penalties associated with heat exchange are avoided. Fourth air systems do not "dump" energy as liquid systems do when the fluid temperature reaches its boiling point, and fifth,

the storage capacity used to generate the f-charts for the air systems is slightly larger than that use for the liquid

1/6 systems. It cannot be concluded, however, that air heating systems perform better than liquid systems. The overall collector efficiency factor, PR is ordinarily lower for air heaters. This paper summarizes a computer simulation by Butz

[81] of the use of solar energy for providing heating cooling and service hot water for residential use. The system is illustrated in Fig. (80) .

1.09

f-08 b* 1 1"0.7 s* 1-06 !*0!> f»0.4 f*0.3 f. f »0 2 f-O.J I fi3'Sb- 4 a h ie— v «rr rjvKCio* A . rtAiucicuo I m f «*** *ÿ The main component of-----the system-----are a solar collector, an energy storage tank, a service hot water system for top use a LiBr-H20 absorption air conditioner, an air hater for space heating, an auxiliary supply to supplement solar energy, appropriate controls, and a residence. This study is based in part on a paper by Lbof and Tybout [82] . The solar collector was modeled in the manner proposed by Hottel and

Whiller [83] , Bliss [84] , and Klein et at [85] in which the thermal capacitance of the collector is neglected. The basic equation is: Qv - FR AC [S - U:l (T0l - TAME ) ] . . . (I!) The collector was "operated" whenever the value of Q was calculated as a positive number. The energy storage tank was

tl7 modeled as a cylindrical insulated tank located within the residence. The equation describing the energy balance on the water in the storage tank accounts for energy gain from the collector, energy removed by the load, and energy lost the surroundings (in this case into the house) , and is given by

Mg Cp d - Wc cp ‘Tco TS)+ÿWL+ WFÿCP *tRN " TS * dt +ULS AS . . . tte> The air heater provides heat to the residence when required.

Hot water from the energy storage tank is circulated through a water to air heat exchanger when energy is transferred to air circulated through a water to air heat exchanger where energy is transferred to air circulating from the room. The air conditioner model include both sensible cooling and dehumidification of the room air and was developed with the assistance of manufactures of absorption air conditioners.

From the anticipated operating characteristics of a three ton unit with low submergence, the following relation for the operating capacity as a function of entering hot water and cooling water temperatures was obtained. Y = 0.0l7258Tn 0.025863 (Tcw 65) -2.1 The unit was modeled as operating at a constant coefficient of performance of 0.65 as experimentally observed by Sheridan and Duffie [86] . The apparatus dew point was specified by the following empirical relation as a function of cooler operating capacity Y: TE = 47 + 15 (1- Y )

//Q The service hot water system model consisted of a small storage tank where water is maintained at or above a suitable temperature, a heat exchanger which provided energy from the main energy storage tank, and an auxiliary heater.

The main auxiliary heater adds energy to the water pumped from the energy storage tank to either the air conditioner or the air heater. This heater operates at two different but constant rates of energy addition. When the room temperature ranges slightly out of the desired range, the load is not being met with the energy available from the storage tank and the first stage of the auxiliary heater is activated. The residence was modeled as a box-like structure with no attic or basement. Each wall and the roof were divided into three isothermal sections (nodes) perpendicular to the direction of heat flow. The interior of the residence was modeled as a single isothermal node. An energy balance was written for the interior where the thermal capacitance was due to the interior walls, furnishings, air in the building, and the capacitance effects of the floor. The energy balance accounted for,- heat transfer through the walls, roof, windows, and floor solar radiation through unshaded portions of the windows,- infiltration of outside air; internal heat generation by occupants and electrical appliances. The equations for each of the components described above were programmed. The integration of the differential equations was accomplished with a variable step size Runge-Kutta 4th order integrator. This is the same data as used by Loof and

IM Tybout [82] in their economic studies of solar heating and

air conditioning. The performance of the system with four r. collector areas can be compared using average daily values

of pertinent energy quantities. Average daily values of the

following quantities were obtained for each month; the

energy transferred to the service hot water system from the

Q ; solar energy storage tank SVC the energy added by the auxiliary heater of the service hot water system Qxs the energy added by the main auxiliary heater QXM ; the energy transferred by the air heater Qah ; and the energy. Average daily values for these quantities are plotted in Figs. (81 and 82) . Table 2. indicates integrated

i 6* \ / v tr r*I'r .1 iv'T't©;• w // / i / . jss i / k\ iiM/K.\ /

r«|r*-*> «—<»*ÿ *1 * h* Fij.gr —

quantities for total energy required for heating cooling

QAC' and service hot water QSVC and the auxiliary energy required for heating-cooling QXM and for service hot water Qxs , as a function of collector area. The total energy requirement for hot water is Qsxc + Qxs and the solar energy supplied for heating and cooling is QAC + QAH - QXM . The total amount of energy required for heating and air

Uc? conditioning were found to be dependent to some extent on the area of the collector. This dependence is explained by two factors. First, the control system was such that with larger collectors, conditions in the building were maintained more nearly of the desired levels. Systems with smaller collectors allowed more excursions outside of the desired range. Second, the storage tank capacity ( and thus thermal losses from the tank) were a function of collector area; as these losses from the tank were to the interior of the building, they subtract from the heating load to reduce QAH and add to the cooling load to increase Qftc to an extent determined by storage tank size and temperature. Fig. (83) 30 -i —r' A< •650 2 -----

O a" Q...xi .inodtnl Solar Energy o 5 £ ,o 5< UJ o 0o.Useful Go»n froin Collector < ffo.W.3 >

0 __ 0 J A 0 N J r M A if T~1 MONTH Fig.|, -- fr system. shows average daily useful energy gain Qv for the 650 ft2 system. Also shown is the average daily incident solar energy QQQL and the average daily excess energy QQVR for the system with the 650 ft2 collector. The monthly efficiencies of the collector operating in this system for the four

Mi collector areas are shown in Fig. (84) . The yearly collector

vr i. t--' •i-r-i-t-l---s—s--i

efficiency is shown in Fig. (85) as a function of

S-.- 5*«j" I- * & "fcil M '*» DILIOO* *H» m*i N f Itmh A•» <•11ÿ- • •! * collector area. Again, as the collector area is increased, the efficiencies decrease. The economics feasibility of this particular type of solar energy system was studied by comparing the annual cost of a solar energy system to that of a conventional system. The annual costs of both systems are due to fuel and electric costs plus sums representing amortization of initial costs. There is an initial base cost of the both systems. The year sum for the initial cost of the solar energy system above the base cost of the conventional system is then CAN - 0.10185(1250+(0.75+Cc)Ac)

122 The yearly cost to operate the additional pumps of the solar energy system was estimated to be E = 0.93AC Ce The cost of fuel to operate the two auxiliary heaters is determined by

F - CF(QXS + QXM ) The total annual cost ($/yr) of the solar energy system is the sum of the electricity, fuel and incremental costs aSOL = 0.10185 (1250= (0 .75+Cc)Ac) + 0 . 9AC C£ +Cr

r tt rv \ X i- I *•!*< *r muMm «S4M%

as a function of collector area, the curves of Fig. (87) were

x

hJ N 3 900 S03 (ÿ \ O' > \fi | v § 400 'N*•» A < N D s \\\, 2 V>> 3001- I , I I , »o *6o . too . •00 COLLECTOR AREA (It1) Ftp- Optimum cullcetitr size at a function of collector and fuel emit. !Ji3> obtained by joining the minimum points of all the curves of

the same collector cost on Fig. (86) and the curves of r. constant fuel cost

were obtained by joining the mimimum points of all the

curfves with the same fuel cost .

A system is shown schematically in Fig. (88) with

I I

W\A/- ! J

J mm IX

tm FU jd>

.'r< r,+s*.

the equipment arranged for summer cooling, the normal

electrically driven air-conditioner has been modified by

B.W.Tleimat to include a water cooled condenser rather than

the usual air-cooled one. Water to be used in the condenser

is cooled by noctural radiation and stored in one of the two water tanks . The second water tankis used to receive the warmed water after leaving the condenser, so that the temperature of water entering the condenser is essentially

consistant and the load on the heat pump is therefore

constant. The load on the heat pump is less than that which

would be imposed by using air-cooling because the

nocturally-cooled water is lower in temperature than the ambient air. The same system arranged for winter heating is shown in Fig. (89) with the water-cooled unit serving

r

I I ft. c*=> llj

4

1 JTiS. sz O- a

W & 8S. V

as the evaporator and the interior het exchanger serving as the condenser. Since the winter heating load is generally greater than the summer cooling load, either the system, must operate for a larger fraction of the tune then in the summer or the capacities of the compressor and heat

(X Sf exchangers must be increased. Thus for a retrofit

application using solar heat, it could be argued that the

adoption of the system shown in Fig. (89) would be more than sufficient to carry the heating load during the cold season with possibly adding an auxiliary interior heat- transfer

unit to the normal air-conditioning unit in existing installation. It is believed that this system would show a

very appreciable saving in fuel as compared with the system

used in the conventional all-electric dwelling unit. The additional equipment required, as a compared with the air

conditioning unit normally found in these units, includes a

solar collector, water storage tanks, a water-cold

evaporator or condenser, auxiliary heat-transfer unit and

circulating pumps and regulating devices. The concept of a

solar-assisted heat pump has been applied in several

previous instances. As described by Haines [87]. The

installation at Albuquerque involved a 7-0. 5-ton

refrigerated water chiller as the heat pump, a solar

collector of 790 ft2 area, a 6000 gal. water-storage tank, and an atmospheric cooling tower. The entire system is used

for heating and cooling the 43 ft2 building. Water was to be circulated through the solar collector at a rate such that

it would be heated to temperatures of 110-140 °F on clear days and to somewhat lower temperatures on cloudy days. This warm water from the storage tank is circulated through floor and ceiling panels for space heating. The heat pump is activated when the water temperature falls to 90 °F because

i*6 of continued storm weather. The cooling tower is used in summer to dispose of the heat from the heat -pump condenser. Bliss [88] , in a description of the Tuceson installation,

indicates that it consists of a solar collector nearly as

large in area as the roof, a tow zones water-storage tank with horizontal insulating baffle separating the two zones

a heat pump operating between the two zones, and circulating

pump conveying water from the tank to ceiling panels for

heating or cooling the space. Yanagimachi [89] describes

his proposed scheme as one in which the temperatures of the

evaporator and condenser of the heat pump are maintain

constant throughout the year at values of 4 and 40 °C,

respectively. Harper [90] described the AFASE house in

Phonix as consisting of a louver-type solar collector a 2000

gal. water-storage tank, and a heat pump with air cooled

evaporator and condenser. Water heated in the solar

collector is stored in the tank and circulated through heating coils in a plenum chamber to heat the air being circulated through the house with the heat pump in¬ operative. In the calculations below the following conditions are assumed.

1. Average of daily temperature of ambient air during the heating season is 45 °F.

2. Average daily insolation during winter is 1000 Btu ft'2

3. Duration of heating season is 5 months, or 150 days. 4. Duration of heat storage is 3 days.

5 . Average temperature of ambient air during the

12 hr. cooling period is 90 °F.

6. Duration of cooling season is 4 months, or

120 days.

7. Indoor temperature is constant at 70 °F.

8. Water-heating and cloths-drying load is to be supplied from an external source during the heating season while solar-collected heat could

supply this load during balance of the year.

9. During heating, the refrigerant in the heat pump

evaporate at 90 °F and condenser at 110 °F

while during cooling, the temperatures are 50 and

110 °F, respectively. 10. The efficiencies of the furnace of the space

heater, water heater, and clothes dryer operating

on fossil fuel are 60 per cent.

11. For extended periods of cloudy days during the heating season, an external source of heat must be available and is assumed to require 10 per cent of the heat load.

Fig. (90) is a schematic diagram of the cycle. In this

system, i Kfor out

2 _ / Ccndeoitr •3 Condtray V I 2 jy \\ f \\ Exponuon ? I valv* \ I \ Evoporotg Compftiior A I A

Evaporator

Entropy 90 / Hoot in Fi® Schemitic (low di*(nm of reveried cycle with iti conwpondini lompcnuire encropy diagram. /?8 Froeon 12 was selected as the working fluid. The condenser is proposed to be air-cooled and would be made of finned tubes which give an overall heat-transfer coefficient [91] based on bare tube area.

If the evaporator in the heating mode is a shell-and- tube unit, and overall-heat-transfer coefficient of 300 Btu hr”1 ft”2 F”1 could be assumed and if water from the heat- storage tank enters at 120 °F and leaves at 85 °F, the evaporator area would be about 17.7 ft*. The maximum heat load on the evaporator in the heating mode is equal to the maximum heat required for building multiplied by the ratio of (h-ÿ - h4)/(h2 - hÿ) . If we assume the collectors to have an efficiency of 75 per cent and the insulated tanks a heat-storage efficiency of 90 per cent, the solar collector would require an area of 480 ft2 . In 1947, Deitz and Czapek built a number of solar test room at M.I.T. to test the principle of combining the collecting storing, and heating functions of a solar hated house into one simple south wall container [92]. In 1967,

Hay and Yellott built a solar test room of similar size in

Phoenix [93,94]. They used a related system (patented by

Hay) in which the roof constituted the combined collector, storage and heat exchange system. Other results including economic and architectural aspects are given by Haggard [95] .

i*1 circuit causes panels to open at the firs opportunity to

heat or cool the water to the temperature set by the occupants on the water thermostat. The potential for heating and cooling was indicated by a "dummy water bag" control- plate whose temperature indicated what limiting temperature the water would approach if the panels were opened indefinitely. In order to thermally simulate the water bags, the control plate was made with a black steel absorber with a plastic bubble cover. Proper control requires that the circuit of Fig. (93) have a water thermostat with a "dead- zone"

|{*.

L*U1I fcfnriMftT --1--1 ] ~j AWIMW __ 4. T h •

>*r i

ITV , t T vvfl; pv,m *i- I »- t \ T : { CV MCIUMUNI I MUU Ml.Ml* 1

F* rw? karwrvi««r> It Hrhnuo i**»*|l- aiW J Fy. 93. — between contacts or else have a switch between thermostats that limits operation to either heating or cooling alone. A 24 channel recorder logged hourly temperatures

/SI throughout the structure as well as wet bulb and dry bulb

temperature inside and outside the house. Fig. (94) shows Thermal oik*rionof * house mines movjl monthly OMTPOOK AVI Util OMIT »«9l - AVtAAGI POOMTIW. / AVIXAGI AOO* » - / »AI1» AAOCf T G $ 4 HTI-? x-t £-W/B .i i OOTCIOO«*VflUOfÿ- .B unv to* -

Ml | | »—» ! Mi | mi. J MX [ Ht |OCT . Monthly I'tr.pr IcMÿmluic. average temperature date for the period between the completion of construction. The house was under thermostatic

control at the temperature settings made by occupants.

Examination of the records indicates that the occupants generally found 2l°C (70 °F) to be comfortable in both the heating and cooling season. Althoughunder to restrictions, the occupants made no use of auxiliary energy for heating or cooling behond that introduced by the normal use of kitchen appliances, lights, etc. As seen in Fig. (94) the diode action of the panel was able co keep the average indoor temperature at 20 °C (68 °F) during February. Daily February temperature changes are shown in Fig. (93), where the rapid rise in water and room temperatures are noted between the

5th and the 10th following a cold startup condi ton. Hourly temperatures for typical heating and cooling days are shown in Figs. (95 and 96). Fig. (95) shows

/.32 800 r PANELS - OPEN /+N 600 / \ s ' P 400 / 3 9 aoo z / 0 * 36 90 30 80 26 -INSIDE AIR 70 H S 20 9- UJ UJ cr CEILINGVO- cc 3 AT 6 FT' / 3 *“ 15 -FLOOR' 60 H cc< cc< UJ I 10 60 ? £ 6 toOUTSIDE 40 AIR 0 30 CONTROL PLATE •6 20 , -10 i i i i i i i I i.-i i .i t A.M. 12 P.M. TIME OF DAY-FEB 24. 1974 9S. Fig.} Hourly temperatures on a typical heating day.

I 31 the panels stayed open for the maximum possible time-opening when theating mode operation whenthe control plate became hotter than the water and closing when the control plate cooled below the water. Fig. (96) shows cooling mode operation with the panels opening when the control plate became colder than the water and closing when the water thermostat setting was reached. The control here was imprecise due to the thermostat temperature differentials.

The efficiencies were found to be predictable using standard flat plate analysis procedures [96] . The efficiency was calculated for the above midday conditions from the equation n « / - Ub AT/I where f = the fraction of incident solar energy absorbed by

the water. Ub = combined convection and radiation heat transfer coefficient, W/m2 °C. At = the temperature difference between the water bag surface and the outdoor air, °C. I = the horizontal insolation received, W/m2 Based on solar transmissivity measurement of the clear PVC film and of the 20 cm of water, the value of f for an inflated air-cell configuration was calculation to be about 0.82 for normal incidence on a clean collector. PANELS OPEN

38 •O 30 OUTSIDE 00 28 ISIOS A! X3 uT 20 70 € z. Ui ceUJ WATER £C B. 15 80 £ s ec< OUTSIDE y / 101n I l DEWPOINT 80 8 CONTROL PLATE' 40

0 30

.8 WATERSTAT AT 07 P. 20 *10 LU .1 . . . J u,d.u L . UJJ 12 P.M. 12 A.M. TIME OF DAY—AUGUST 22/23. 1974 Fig96. Hourly temperatures on a typical cooling day.

f3J- Fig. (97) shows the estimated disposition of energy

msMj TOTAL ISOLATION ON 1100 FiJ BAG AREA su m WHILE A LOSS WHILE LOSS 1 PANELS OPEN PANELS SHUT OM MJ INSOLATION INCIDENT WHILE PANELS OPEN AVO. AMOIENT TEMP. 7.77CnJ n IN GLAZING | I MJ nEVLECTEO ft ADSORBEO

401 MJ AVG. i ABSORQEO IN WATER WATER TEMP. / 117MJ 7% MJ TRANSf ERRED INHLTHATION r“-o AVO. ROOM FROM CEILING 47.t MJ TEMP. AT S PT. 17. MJ 91MJ frUN THRU GLASS CONOUCTLP, GLASS PELiPLI• "1 r> V. 117MJ 4S.7 MJ CONDOCUO, WALLS APPLIANCES 1 30MJ 30 MJ -- SLAn SUN ON WALLS CONDUCTED. V ----- r 97 i I'ig. Energy How on a lyrical healing day.

throughout the house on 18 February. The daily average

temperatures and heat flow shown in Fig. (97) are based on a steady-state heat balance calculating using daily average values for inputs. The heat transfer coefficients for the various building components were either measured. The measured daily swings in indoor temperature were also found to be predictable using heat balance calculations based on the thermal admittance concept discussd by Bassett and Pritchard (97] . This system is designed for cooling, heating and hot water supply by solar energy or 1930 m* air- conditioning area at the hall and dining room for staff members in 6766 m* of the Neuropathy Ward in the Hospital of School of Medicine, Kinki University discussed by Katsuhiro Hinotani . The structure of the evacuatd glass tube solar.

I2 6 collector is shown in Fig. (98) The glass tube used as the

? : es* :-w2':.v Ss L T dmi M06_ 2050 a-UJ3O 2.195

MAX 18 @JS)CU ,8r. rf I iY

'6 S ProntHv cov«r $U3 304 8 Slay * SUS 316 7 Dhomt tH* I DCuT 6 G*«ff I Bo 3 Plan tuba ) SK 4 $i«m B I NWS 3 St«m A NWS 2 i OCuP 'BoT •9P. fig- Structure of evacuated glut tube collector.

collector tube is lOOram of O.D., 2mm in thickness, 2050mm in

length, and its material is eodalime glass. Inside the glass tube, a collector plate of 92mm (W)x200mm (L)x 0.3mm (t) is placed longitudinally in each center forming a projection to which a collector pipe of 14$ in O.D. is inserted and

brazed. The absorption and emission characteristics are

shown in Fig. (99)

100 100

90 RafJadOnc* 90 80 Abtorptonc*, \ -----— Emlionc* 80 c % 8 70 70 § 8 60 \ 60 & 30 g 1“40 2 \ 40 f if 30 \ \ 8 20 20 % \ a. 10 s,» 10 a5 0 Ql 03 1.0 &o IOO 2Q0 1 '»• Wovtt«ngih, fi m fig. The abiorplion and tmituon chancteriilici of the (elective lurface. /37 Analysis of a flat plate type solar collector has been made by Duffie and others [98,99], in detail, and basically, the same analysis is applicable to the evacuated glass tube type solar collector as well. The differences between the two

types of collector are that the glass cover surface is cylindrical shape and that the clearance between the collector plate and the glass surface is in vacuum. The average transmittance into the glass tube is obtained by the incident angle ©Q of the incident light into the collector plate.

T(d0)= cosOdB

where, x (0) is transmittance, which is derived from the reflectancep . That is *(©) = (1-p)/ (1+p) -(M) and p(©) = (1/2) {sin* (©'- ) /sin* (©'-©) +tan* (O' -0) /tan* (6'+0)}, where © and ©' are the incident angle and refractive angle on the glass surface, respectively. The refractive angle ©' can be derived from the refractive index of the medium n' and n by Snell's law. sin ©' = (n' /n) sin© The collected energy by the collector tube under steady state is obtained by the following equation: Qu = Ac FR <«1 - (Ap /Ac) OL

I1& Where AQ is the area of heat collecting surface, Ap is the area of the collector plate, FR is the heat removal factor, is the product of absorptance and transmittance, and UL is the overall heat transfer coefficient. The heat transfer coefficient is calculated from the thermal

resistance between the collector plate and glass tube and

between the glass tube and the exterior as / —(& UL = l/{l/(hw + hg-r )+l/(hp.g + hp.r )}

where hw is the heat transfer coefficient of glass surface hg . r is the radiation heat transfer coefficient from the glass tube surface, g is convection heat transfer coefficient from the collector plate surface and hp.r is the radiation heat transfer coefficient between the collector

coefficient on the glass tube surface is approximated by the

heat transfer coefficient around a cylinder. By Hilper[100] l

4

+(W-D)F) (?J 1/UD = W[1/Ul(D +1/Cb +l/nDihf where W is the fin width, D and Di are O.D. and I.D. of the collector pipe, respectively, I/Cb is the contact resistance and F is the fin efficiency, hj is vonvectionheat transfer coefficient inside the tube, which is calculated from the

/(fD (i) for L/Di 0.0048R 167) Nu = log [1/{1 - 1/ (V (RePrDi/L.Pr0* °) }] (ii) for L/Di > 0.0048Re Nu = 3.65+0.0668/(1+0.04. (RePrDi/L2/3}

and when Re > 3000.0 (iii) Nu = 0 .036Re 0.8 pr 0.333 (L/Di) -0.054 where. Re = vDi/V and V is the velocity of fluid and Pr is the Prandtl number From equns ( Z> ) ( T ) , the collected energy Qu can be calculated. Fig. (100) shows the layout of the solar

u.,

tl 1 1 ] i [ n 1 1 1 1 1 1 it i 1 1 ( j \ n 1 1 ? 1 1 1 1 1 1 uf Ftj.lOD. litinwiwimi iiHiimuuiilÿ «-j n ; ; n i 1 1 1 1 __ ' __

collector and Fig. (101) shows a view of the solar collector r / i

7 / r ftt.lOl- Wl 3

L

Fig. A view of (he soiar collector lyilera in (he Neuropathy Ward of the hoipital. system in the Neuropathy ward of the hospital.At the installaton of the solar collector, eith collector tubes were connected in parallel and used as a unit. The measuring.

Ui! An evacuated glass lube solar cooling, healing and hot water supply system 54|

ill pyranomeitr > n HWST I : 'motofton /Q Amo. temp U '• Inlet temp of collector U“f\t : Outlet ttmp of collector F : Flow rate

& °X

V A 45 Ns V

pump flowmeter

20.0 O July, 1977 Aw 18.0 • cooling * •S*p* •#' •Oct. s!= lft.0 - •Nov. Dec. e •Jon., 197ft * 14.0 rworing e •Fob. ? •Mor. e •e Apr. 9 hoi wotor supply 9, •• Moy 9 ,ao • f'“5 c Jun. coding .1 v •July » ao o» 9 • 9 Mi 9 6 0 9 \ c»

9. F/J.IO. 40 9

2.0 7-# : 0 to 20 23 Insofolion on collector surface

Fig. Daily colkeior performance.

/w points for the performance of this cooling, heating and hot water supply system are shown in Fig. (102) . Based on the data obtained on the operation of this solar energy cooling, heating and hot water supply system for one year, daily energy collected insolation characteristic of the evacuated glass tube type solar collector is indicated in Fig. (103)

i i j" i— K5> J: LJ — /ÿ 1“ rr A 1“

i o — WII

The monthly average of the insolation on the collector surface, ambient temperature and inlet and outlet temperatures of the collector which are related to energy collection-insolation characteristics, the maximum and minimum values of the insolation in each month, design value of the collector temperature, and alsothe demarcation of cooling, heating or hot water supply operation. In Fig. (103), the averages of inlet and outlet temperatures over 15 min interval are calculated apart based on the data of the inlet and outlet (at three and nine points respectively) temperatures of the collector measured every

5 min. and then the amount of collected energy for 15 min

is figure out by the multiplying the temperature difference between the averaged outlet and inlet temperature of the

collector by the flow rate. Fig. (104) indicates

!" fiy. tori',

a— nut n'

the instaneous collector efficiency between 12.00 and 13.00.

Each point in this figure shows the collector efficiency calculated from the integral values of insolation and heat collection for 15 min into that for 1 hr and the values thus obtaained for the past year are plotted. As the abscissa, x = (Tin - Ta )/I was applied and Tÿn and Ta are the average temperatures for 1 hr. By interpolation of these points, the efficiency line is obtained at the following

Y = -3.12 x + 0.80.

Hit, Fig. (105) is to show the hourly collector efficiency in each

•• %, :: v> “ v.. v S- -rr-*r fr

« . A. t- t*.,. •V- «1 £ r. a *tr Tr "tr

V •V.: M V M V tr TT Vr i—»r * —«—rr •—«—Ltr F/j.\o*r

representative months for cooling, heating and hot water supply seasons. The addition of solar cooling capability to a solar space and domestic hot water (DHW) heating system allows for a substantially improved usage of the solar collector array and the associated components of the solar system. Year-

round usage gives greater cost-effectiveness of the solar equipment. An integrated solar heating and cooling system

(including DHW heating) is expected to achieve a much lower cost per unit energy than a solar space and DHW heating system in most areas of the continental United States [101] . Ward [102] has shown that solar cooling would typically provide a nearly constant per cent of the summer cooling load on a daily basis (with auxiliary providing the balance .

/

days (no auxiliary use) , and largely auxiliary on 20-30 days

furing the heating season. The particular characteristics of

the evacuated tube solar collectors, also play an important part in overall sysem design. For example, because of the

geometrical shape of evacuated glass tube solar collectors,

snow removal requires longer melting periods than conventional flat-plate, solar collectors because snow slide-off is generally impeded by the tubular design.

Evacuated tube solar collectors permit the use of

a vacuum of sufficient magnitude to virtually eliminate convection and conduction heat transfer losses. In addition,

these collectors generally required a minimum amount of material per m2 of collector and thus provide for the possibility of lower costs (under conditions of large scale manufacturing processes) . Finally the vacuum may help to

protect a selective surface used on the absorber (for

reduction of long-wave radiation heat losses) against preformance legradation over the life of the collector. The performance of these evacuated glass tube solar collectors

can be represented (for steady-state conditions) by the

standard equation. n = Fr(T*) - FRUL(Ti-Ya /HR) where n is the solar collector efficiency (Dimensionless) FR(T«) is the solar collector efficiency when (T— Tft) = O.UL is a function of the various heat transfer coefficient applicable to a particular collector (kj/ [hr] [m2 ] [c°]),Tj_ is the inlet fluid temperature (°c) rT# is the outdoor air temperature (°C) and (HR) is the solar radiation on the collector (kJ/[hr] [m2 ] ) . For comparison purpose, value of FR(T«) of FRUL are given in table 1 for several different kinds of solar

collector, Equation ( ) can also be used to estimate the

maximum temperature that may be reached during equilibrium

conditions and when there is no flow of coolant fluid through the collector loop. Under these conditions n = 0 and eqn { ) reduces to:

Ti = HR (Ttt) + Ta ... U3 ) UL It will be noted that the values of Fr (T«)

are lower for the evacuated glass tube solar collectors compared to the other more conventional (concentration - 1) flat-plate solar collectors listed, and as a result, their .

47 equilibrium {no flow) temperatures are also much higher.

However it is important to realize that heat losses from evacuated glass tube solar collectors are dominated by thermal radiation. In this case, UL increases with the their power of the absolute temperature of the absorber, and because the equilibrium (no flow) temperature of evacuated glass tube solar collectors are so high, substantial increase in the value of UL can be expected, if we assume that : UL - CT3ia ov where C = a constant, kJ/(hr) —(m* ) (k4) , and Tia = Ti + 273°K absolute inlet fluid temperature, °K . Substituting Gattajbcn and the above expression for T3ia (Tia - 273°K - Tq) = ItalHR C The solution of eq««v7*>-j for Tia by trial and error. Let Qu represent the heat delivered by the collector in kJ/ (m* ) (hr) , then _Qu- = FR(xti) - FRUL - Ta) - cW (CfTi /At) HR HR HR where AT.ÿ = is the change in collector inlet fluid temperature (°C) during the time interval At, and At is the time interval (hr) . For the Owens - Illinois collector, equATY<3vj becomes __QU_ = 0.791 - 3.59 ( T± - Ta ) - 77.6 (AT±/At) HR HR HR The effect of this large heat capacity can be seen if we consider the conditions of = 50°C; Ta = - 10°C,-and u AT/cyq Ti ' (Tÿ at a time = 1 hr before) = 10°C, then eqi becomes

(m* ) (hr) kj/ (m2 ) (hr) Qu = 0.791 HR - 215.4 kJ/ - 4656 A study of the second third terms on the right

side of this equation demonstrates the significance of the

energy required to heat the evacuated tube collector to

operating conditions in relation to the steady state heat

then five per cent of the energy required to "warm up" the

collector. Of equal significance is the fact that most of

the heat stored in the solar collector when it ends its

daily operation will be lost overnight. There are several

variations in the design of evacuated tube solar collectors: in addition to the corning and Owens-illinois collectors,

which are utilized in Coloroda State University solar House

I and III, respectively. In general, arranging the collector

modules in parallel flow patterns (rather than series flow

patterns) reduces the total pressure drop through the

collector a array. However, these parallel flow patterns do

require careful design if uniform flow distribution is to be achieved. Experience indicates that attempting to obtain uniform flow distribution by trial-and-error adjustments of either values of dampers is essentially impossible in solar collector arrays and, consequently, uniform flow distribution must be designed into the array from the outset. Other difficulties associated with the use of water and water-glycol in evacuated tube solar collectors are the

potential for freezing and boiling. The freezing problem is

relatively easy to avoid by using a liquid with a sufficiently low freezing point. If an ethylene glycol water mixture is used, sufficient ethylene glycol must be added to permit flow under all conditions. It is possible to use

lower concentrations of ethylene glycol than that specified by the manufacture to prevent damage to the collector, but

flow will not be possible. While the use of ethylene glycol or other non-freezing liquid may solve the freezing problem,

the potential for power failures over the life of the system virtually assure numerous opportunities for boil-off of the collector liquid. Fig. (106) is a A Ml.* A lltiH* A V? =3 A«i OMW *»•- iMl *••1 OHS LMI TIM — ___J on« ftS, ClK 3

VI 1*3. 15.

(Mlllf ___J IlMif ]A._ Cli *1A* •r:MM VMAMM j IaiM hnu, tad c 'V M i)Mr* ».k r*K. «M! uM Mb tadnua design schematic for an integrated solar heating and cooling system. It incorporates evacuated tubular solar collectors a thermal storage unit, an auxiliary boiler (For providing

IbO conventional heat to the heating coils or to the absorption

chiller) , heating coils, cooling subsystem (see below) automatically actuated 3-way valves and a DHW preheat

system.

The design of the cooling subsystem must consider not only

the operating characteristics of the absorption cooling

unit, but the other components of the solar system as well.

For example, if the thermal storage unit is located within

the conditioned space of the building, then any heat losses

from the storage will add to the cooling load and thus degrade the performance of the total system. Heat losses

from a liquid thermal storage unit can be very substantial and can, if fact, mean the difference between a successful and an inadequate solar cooling design. Not only do heat losses from storage add to the cooling load, but they also detract from the ability of the solar storage to provide heat at sufficiently high temperatures to operate the cooling unit. Jacobasen [103] and San Martin [104] .Ward

[105] has shown for example, that an inlet temperature of

ib"! the generator of the absorption unit of 88 C may provide for a COP of 0.6 (for cooling water temperatures of 30 C) . If reduced to 0 . 5, a cooling subsystem design that incorporates these considerations is shown in (Fig.107) This design utilizes two identically sized water storage tanks (designated as "warm storage") with the total volume of water in the cooling subsystem equal to the volume of one tank. The use of two variable level cool storage tanks insures the all-important temperature stratification between the inlet and outlet sides of the water chiller. In addition the chiller can be run in a continuous fashion to avoid cycling of the absorption unit under conditions of intermittent load. Finally, the proper use of automatically actuated 3-way valves allows the use of a single pump for the chiller and cooling load loops. The position of these valves and status of the cooling subsystem pumps are detailed.

Further Nobuo Nakahara described the experimental study on house cooling and heating with solar energy using flat plate collector . The system outlines are as following: (a) House, One-story.

(b) Collector. (c) Absorption refrigeration machine.

(d) Heat storage tank.

(e) Auxiliary heater.

(f) Automatic control system.

The area of collectors and the capacity of the heat CT Pump Circulating J Loop Cooling *.U%% 111 Towor Chi I lor ( Genorotor )

Blowar II f vi r j i B s k._ i m1 Cooling Tf { V2 Coils L __ B il E I Worm \ Storogo Cool Storage Supply Air I A' Cool Pump S-0V3 tor. Fig. Solar cooling subsystem schematic.

IS3 storage tank were designed so that the quantity of heat

necessary for space heating might meet nearly that of solar

heat collected in a clear winter day, since the main object

of this study was not to install and economical system

itself, but to get useful data for a future economical

system. Fig. (108) shows the

OFFICE ROOM ( ) SOLAN COLLECTOR | > i II EAT I\r. CYCLE ADSORPTION ' HKAT STORAGE TAKE REFRIGERATION MACHINE A KANCOIL DM V j y COOLING CYCLE -- 1 > A - | FHKK/.fNG PROTECTION ! CYC I K t k if ml —E Gr I ”> AUXILIARY j COLLECTOR PI'MR COOLING WATER HEATER -A..-. GAS Fig. Simplified flow diagnim of the system. FiJ. 10 &

simplified flow diagram of the system. In the figure the

solid line, the broken line and the dot-dash-line show the

water flow in cooling cycle, heating cycle and freeze

protection cycle, respectively. By the command of the

temperature differential control between the supper final

part and the lower initial part of collectors, the collector

pump starts and stops. The high temperature water (in the

upper zone of the heat storage tank) and the low temperature water (in the lower zone) are mixed up by 3 way valve to maintain a constant collector inlet temperature, and the

flow rate is controlled by a 2 way valve to maintain a constant temperature difference between the inlet and the

\*

temperature in collectors falls down nearly to the freezing point, the collector pump starts and the comparatively low

temperature water in the lower zone of the tank circulates

through collectors in order to protect them from freezing.

This operation does not badly influence the stratification effect. The gas fired auxiliary heater is installed near the

tank and heats the water in the upper zone. The agitating pump intermittently operates when the upper zone temperature exceeds the high limit. The secondary circuit is open in

winter, and closed in summer. In winter the temperature of

water supplied to fancoil units is controlled to be constant by mixing the high temperature water in the upper zone of

the tank with the low temperature water in the lower zone,

in order that the stratification in the tank may not be badly influenced. Fig. (109) shows instantaneous efficiency of 5 y « 4 . 8

S I s I* I |W"«I g y » Hwmm *r.—' - i solar heat collection at noon both in winter and in summer.

The efficiency is defined as a rate of collected solar heat to the solar radiation transmitted through glazing, and can be approximately represented as a straight line related to regardless of seasons. It is well-known that transmittance of glass varies with solar incident angle, so these data are

chosen only at noon, when the angle is nearly normal, and further, Tt< is defined as solar radiation collector efficiency for a period both in winter and in summer.

rjft is instantaneous efficiency at noon, while iÿ2 and are seasonal efficiency described by the solar radiation during collection and by the solar radiation between sunrise and sunset, respectively. The average temperature of water supplied to collectors was 45 C in winter and 75 C in summer. The collector tilt angle was 50 in winter and 10 in summer.

Fig. (110 and 111) show the hourly change of

VV| »•MIIIIM H •tjvvfifjilb'w / •4.r V<

> ttll <•>>!< " -i‘ i i f.j y.i ui.iiui /• II •I £* C ft*J. no. f ;| . f. I : i t A 4 i •t i 4 Jn t t •4 J -4. •~ —'I** - *mm4 wimm f mu-- —

«*4 *44**1 t* C l1I I I *>ÿ «l Ft ro *> ii rl -t- ifffdfMv or 00 :| •» 0 J 9 tjji “ J" JlI » IBJJiJrrbiir /«* * * •UK — OuUI* •(«ÿ<«!< X in J — r«N illiU i©a & M ro •o ’0 CAiUVS «0 to •o «c OuTWI *« • S. lo /> rM . T- •l>H( - M.1 4,1't uru H«« t.ort

ir6 instantaneous collector efficiency for a few clear days in

winter and in summer, respectively. At the pattern of

Fig. (110) in which the collector inlet temperature was kept

almost constant all day long, the temperature of the upper zone of the tank at the starting time of collection was high

enough for the 3 way valve control to work normally in the

intermediate position. That means whether the auxiliary

heater might have operated in the night or the solar heat

collection on the previous day might have been so much as to

be carried over. As solar heat is being collected, the high

temperature zone in the tank spreads downwards and

occasionally gets to the bottom, which results in the second

cycle of heat collection and much higher rise of the inlet temperature as shown in Fig. (110) . Fig. (112) , which shows the similar pattern, verifies the ia .n,» LO TIM» 7 9. 8 16 15 SS 08 £3 9 at St; td

t-4 U 5g si “

0 30 “5s To A! rc •Itt* TEMPEBATOItfi Ft*. » Temperature dittribuiion of w»ter in Ih* heat ilotaje tank. above mentioned stratification phenomena. The pattern B of the same table and figure shows the data of another kind of operation. Fig. (113) shows a typical

Ifl 25 z. t \ Ilni.AH lit AT 3TONA1.E 20 15 f \ i 15 SOI AM lit AT COLLECTED t V.. 3

/ io io X / *. *10 / 3 j * / 5 MEAT I>033 rncm STOWAGE TANA . / TO trpiiOt*l>lft% A l H - 14 15

NEAT CONSUMED OS HOUSE HEATING HI AT LOSS BT i . r uOnilATlON ON PRESSING PROTECTION -10 Typical pattern of heat balance day in a in winter. Hi profile of heat balance in a clear winter day. Solar heat collection started at 8. a.m. when the heat storage was not much because of the lack of carrier over heat and auxiliary

heating in the night, and because of the heat loss from the

tank and the heat dissipation caused by freeze protection cycle. Fig. (114) •iia*t 0 a rmi'hi imt I «»r •*»l* r«Mil i«m I MI r »•!•»•« 11 jf

1.0 KW capacity 0.9 op° 7 2D •U • 08 •’.V"*. >* >- 6 0.7 % \ -• u CE u X# 5 0.6 - 2' z> £ \~ . u< 0.5 ttmp#ratur# 4 0/. .7 from evaporator *75*C 10 to condtnsor 160*0 3 70 60 90 •c TEMPERATURE TO GENERATOR Fig. Measured COP and capacity of absorption refrigeration machine. Flow rate: Generator water 15.0L/uiin; Chilled water 16.0 Umin; Cooling water 32.5 L/min. shows the actually measured coefficient of performance and capacity of the absorption refrigeration machine with the variation of the generator inlet temperature from 70 to 95

C. As the temperature rises, the coefficient of performance drops, while the cooling capacity increases. Therefore,

i s'a these data may not be generally available owing to its low condenser water temperature but the inclination of such performance is thought useful enough, as the higher coefficient of performance of the absorption refrigeration machine can be obtained if the capacity be sacrificed.

Fig. (115) shows the results of cooling operation in

t “R

' PWlOlVC K * or or am 10 ' B» «• m

f—ar •14 T WHO W MUT ,, not (Otuw __ Mil wlla ii 4 nucw IDHU' (tin fcftia utm . u—i •»h«<

M MM" *d d -.!•d i urn i~ ~ Th Ti—r-*-r

a clear summer day. At 10.05 a.m. the generator pump started operating, as the result of it the chilled water temperature fell rapidly and the space cooling began. As the fancoil units are directly connected with the absorption machine without any storage tank for chilled water cycle, the temperature often falls too low if cooling load is not so much.

Some investigations on effective utilization of natural radiative energy have been done using a non- selective type energy have been done using a non-slective type solar collector-sky radiator (NSCR) which acts as a non-selective type solar collective type sky radiator at night [106,107,108]. Fig. (116) shows

nJ vcTT F

. . >fl»W |J|*J«— l»V NKI W MW ->i*4 >r~“* n«nu(n •4 iitri%>i llf* KM lAfkrllL', f. i.« irtrr- !-•"r» INMC. --) MJ wkrkii lUH..---- - —-Ivliirv solar radiation and blackbody radiation at 360 K, together with ideal spectral reflectance of a selective type solar collector (SC) , a non-selective type solar collector (NSC) and an SCR surface. The SC surface has spectral reflectance that varies greatly from one spectral region to another. The

SC surface effective captures solar energy in the high intensity visible and the near infrared spectral regions while exhibiting a poor infrared radiation property.

Therefore the SC cannot act as a sky radiator using atmospheric windows at night. Thermal radiation loss ratio y of SC vs SCR is defined as follows:

Y T) dk/f“a(XT) dk, . . . (if)

where e(h,T) is spectral radiance for a blackbody and T is temperature. During the course of radiative cooling experiments, we discovered that a specular aluminum plate coated with 9m thick KF-Film reached lower equilibrium

Uo temperatures than the reference "black" radiator surface [109] . The spectral reflectance of the surface is shown in Fig. (117) .

Bf-niMJiaCn—r i

/.’•ill-. —t—t t i> t, -r Ik •«*«.

The spectral transmittance of the film is shown was in Fig. (118) .

I f 0.5 Fy.//?.

J t J t rb ft rtr

Tniumiuw* of polytikjrtcn* Him.

For reference, a NSCR was also assembled which was identical to SCR except that its black cooper plate was painted with black paint. The experimental system consists of outer and inner instruments. The outer instrumenmts consists of two solar collector-sky radiators (SCR) and NSCR) , awater tnk, a water heater and cooler, a pump and 13 sensors. The inner instruments consist of an AD converter and a microcomputer. The collective efficiency 7? , the radiative efficiency the ratio of the temperature difference A T to the insolation J and the dimensionless temperature difference were calculated

/<*/ k-!9 using the following equation ( ) .

tic=pco(rout-re) /at, (/*)

AT/J=(TP-T0)/J, U7J

nr“pcv(T,n-rolJC)/(i-«#jty) or*A

—( ( ---- Tf»4 r0-rp) / (1-e.jty) r0 ' where p, c and v are density, specific gravity and volume velocity of water, respectively, TQUt----and Tin are outlet and inlet water temperatures of the collector-radiator , A is the area of the collective-radiative surface, TP = ; SCR NSCR

0 0.1 AT /J Rg. Comparison of ihc collective efficiency of SCR and NSCR.

collective efficiency for both collector radiators. Also

shown in this figure are least square fits of the data

points. Comparing these two curves, it is obvious that the selective type has higher collective efficiency at values of 6T/J greater than 0.03. This behavior is consistent with the concept that SCR heats fluid warmer at daytime than NSCR

(62 as described before. However, both collector radiators have lower efficiencies than conventional SC and NSC respectively for both collector radiators. Fig. (120) shows

1.0

c*0.5 \ SCR Fiji20.

o r, IX) Fig. Comparison of the radiative efficiency of SCR and NSCR.

radiative efficiency for both collector-radiators. Comparing these two curves it is obvious that the selective type has higher radiative efficiency at values of xr greater than 0.25. However, the difference between them is small. The reasons for this small difference are the imperfect selectivity and the high humidity of the experimental place in the suburbs of Nagoya .

/6$ , Table: 3.13:

Time and Day Hourly Radiation/ Daily Radiation ( %)

6-7; 5-6 1.42

7-3; 4-5 3.80 8-9; 3-4 7.40 9-10; 2-3 10.45 10-11; 1-2 12.72 11-12; 12-1 14.21 c .2-

•H 20 _ T3 £X Vi o Wr-! .-f —T3 57 o e rHu s >i •H fl 10_ Q

€ O' H3 V €> > < >1 JC 4Jc c £

C I I I I I -v 1965 70 75 80 85

YEARS

Fig 3.12 Annual variation of Monthly Average Daily Global Solar Radiation at Karachi ,Pakistan

's CHAPTER- II

2.10U Information on global solar radiation are important for quantitative study. Scientists and workers in this field are interested to have more knowledge about solar radiation so as to assess the possibility of their utilization to cover energy crisis. All the countries in Asia, south-east Asia, Africa and Europe are involved in research work.

Similarly solar radiation masurements on horizontal surface are being at Quetta and in four other places . The monthly and annual average of global solar radition data from 1970 to 1991 is presented in table (i\).

The figure (A) shows average global solar radiation averaged for eleven yers. The trend of variation is same for the averaged data and is almost identical with high values in the months of June and November and depression is July and

August. It could be seen that for Quetta that annual values of global radiation varies between 17.44 to 20.68 (Kj m ) .

The highest mean in June (22.89 ) and lowest in December

(12.98 ) the highest recorded total for a month was in June

1990 (26.90 ) and the least in January 1988 (9.10 ).

Distribution of Global Solar Radiation

at Quetta.

The extraterrestrial, global, direct and diffuse component of solar radiation on a horizontal surface have 'HtTTdJ SKY CONDITIONS RAC144 :2 *

). 75—I A Rb & • & H / H — — 4» •N a/ H o \ 0 \ / \ /

0. 5C H

f Ts. / M S / 0 / /

/r \ / \ / \ / 0.25 M *_d ___ H •— _-.Sd •— --- ~ •--•- II 0

1 1 1 J r M A M J JL A S O N 0 Mon tills Fit} 3.f'. Sky conditions nl , Pakistan 0

0 - o

O »./ O • / V\ "o— j / \

nb ' s t

0

V" 4 Hd ' "''ii- ' o 1 J__L 1 1 I J F M A M J JL A S O N I M' tha Fiy 3. Solar Kadiation at QwLifo' Pakistan ft / been estimated. The relationship by Prescot [110] for the

estimation of global radiation and that by Klein [111] and

[112] for cloudiness for the estimation of both diffuse and

direct component of radiation are recommended for Quetta. Figure (B) shows a plot of these factors. The characteristic distribution of solar radiation

at Quetta shows interesting and encouraging results . The extraterrestrial insolation H was calculated using o

H 24 r I ( cos cos S Sin W + 2»ÿsin sin(j~ ) . . (2o) o Sc 7r 360

The is obtained if parameters such as 6, r and were known .

In table ( ) values of H , H, and H are shown . o 4. b 2-3 Sky Conditions at Quetta. The fraction of the extraterrestrial radiation that

reaches the earth's surface as total (global) radiation is

a numbers of the sky. Clearness index as defined by Liu and

Joradn [113] is : K H . . Ul) T - H0 where K is cleanness index, H is monthly average daily

global solar radiation reaching on a horizontal surface and

H is the extraterrestrial insolation on horizontal surface.

Variation of cloudiness is primarily responsible for the day

to day variation of the daily total as well as diffuse radiation during the whole month. The variations of average

lb* clearness index K_ÿ over Che yearsÿ and ics sub-numbers alongwith other ratios which are indeed important for sky conditions at Quetta. The index is minimum in July and August i.e. 0.48 (Mj m2 ) . Also /H reaches maximum value for July and August 0.49 (Mÿ m ) and Hj /H is 0.23 (MJ m1 ) in July and August, this shows that the measure of clearness index in Quetta be approximated by /H instead of H/Ho. Also plotted along with these is the ratio Hb/H showing the contribution of direct radiations. The relations being used are 2 3 = 1.390 4.02TK + 5.531 (K ) 3 .108 (K ) . . (2 VH T r r VH = 1.00 1.13Kr . • US 0.958 0.982K . Hÿ./H = T . Ulr Hb = H - • - UiJ The sky is clear in July and August so 60% of the extraterrestrial radiations would reach the earth's surface. In winter Kÿ_ has high values. The extraterrestrial, global, the estimated diffused and direct component of radiation from (ÿ) produce a symmetrical average distribution of solar energy over the months. So it is recommended for calculations at Quetta.

.Diffuse Solar Radiation Estimates on Horizontal and Tnclined Surface at Quetta.

Estimate of monthly average daily diffuse solar radiation as a function of clearness index has been obtained from Quetta. Data for diffuse solar radiation is not available in Pakistan and the knowledge of the diffuse

Ikb 10 , — I, E G E N 0 a ff- o o 1957-66 b 1967-76 C 1977-65 <• a jÿb

« f t \ \ 10 / - \ //. *•. \ k • s //* / • \ i-..••

10 _

0 1 1 1 J F M A M J JL A S O N

Months Ki«.;}./) Monthly Avocayu Daily Global Solar Radiation at HJLBZL- , l’ak istan Monthly A roragm dally Global Solar Radiation on a Horizontal Surf mom . at Qumtta.

Yonr Jan leb March April Kay .hmc Inly Aug Sop Oct Nov Ikx Annual 1 9/0 16.41 19.55 23.66 26.40 25.07 23. 19 18.84 18.71 18.38 20.64 18.46 15.91 20.79 J97I 16.12 18.84 21.73 22.73 23.99 21.00 17,62 14,65 21.06 18.59 16.54 15.28 19.06 19/2 16.16 18.63 21.56 22. 10 24.07 25.12 20.14 21.89 22.86 22.19 19.13 14.32 20.68 19/3 16.8/ 18.61 22.35 23.40 24.40 211.39 16.20 15.28 17.21 18.88 19.36

19/4 22.73 24.91 21.31 20.4/ 17.79 19.55 20. 16 16.70 16. /ft 19.93 19/5 15.87 18.46 23.02 22.19 22.77 27.88 24.% 19.34 23.14 19.63 17.71 14.69 20.77 19/6 14.32 16.95 18.63 22.06 23.57 23.90 19.63 19.34 19.93 16.83 15.49 19.15

19// 16.70 J 9 . 09 21.18 20.60 21.89 21.14 20.34 19.30 22.2/ 18.1)4 15.8/ 14. 15 19.21 19/8 M84 20.26 19.63 18.34 15.45 I9.U) 18.33 14.81 12.81 12. Hi. 1/.44 1979 15.12 16.66 16.32 17.39 18.78 23.% 25.12 23.57 20.89 20.2/ 17.92 145/ 19.21 1*180 16.35 1/-04 21.65 22,03 24.28 23.49 18,76 18.04 20.48 18,7/ 1 7.00 14,40 19.31. 1981 J5. 19 18.55 20.84 23.50 21. /I 21.0/ 20.71 22.59 18.96 14,83 15.1*8 14,24 18.98 1982 15. 13 16.23 20.72 22.96 21.63 21.98 18.52 16.93 20.20 lo.ai 12.85 J3.03 18.08 i'*83 14. /I 15. % 18.53 20.42 21.17 22. 04 17.36 14.53 18.33 18.2/ 14.91 13,39 I/.49 1984 14.83 1/.22 19,78 25.34 75.42 72.48 14.60 10.75 17.M 18.% 16.46 17.91 I/.96 19ft* 14.16 18.52 19.09 23.65 22. % 22.73 18.1/ I/.06 77,01 I/.56 14.89 13 36 18.66 I '<86 16.41 13.39 70.0/ 71.96 75./0 14,99 15.89 71.78 19.08 13.46 IH.I.l mt 13.69 14.35 9,91 71.18 22,15 24.96 24.26 21.21 19.15 16.59 13.94 11.06 l/./U 1*188 9, 10 13.58 13.64 20.99 18.19 20.01 20.39 21,62 19,26 15,25 13.02 12.13 16.47 I*i89 11.37 14.06 18.74 22.26 25.06 72.34 76.41 26.43 72.36 15.58 14.60 12.81 19.34 199(1 10.M 12.97 18,5/ 71.34 24,61 76.90 24.75 22.64 71.63 19.16 15.53 12.45 19.76 J 99 1 11.45 13.08 21.31 71.13 76.15 75 49 73.44 71.92 19.38 14.3/ 09.45 18.96 Kean 13.16 14.39 17.44 22,01 22.64 77.89 19.44 18.1/ 20.33 18.34 14.28 12.98 18.88

(< 10 0 —,

DIRECT o O u c o o 0 0- 50 _ r: o +J \ "j n x X !t it x DIFFUSE .1 __ X “ -X 'M — — X— X n - i i — — — —o — —i

0 1 i 1 1

J F M A M J JL A S O N D Months

Fig 3.D Percentage Variation of Direct and Diffuse Solar Radiation at component of the global radiation at a site is very

important to the design and the assessment of solar energy.

Therefore, in the absence of measured diffuse data, some methods are suggested.

For the prediction of monthly average diffuse radiation on a horizontal surface, two methods have been described: (i) monthly average diffuse radiation expressed in terms of

the fraction of the maximum possible sunshine hours and (ii) monthly average diffuse radiation, expressed in terms of cloudiness index. The ratio of the diffuse solar radiation on inclined surface to that on a horizontal is calculated for vertical orientation (0-90) . The global solar radiation composes comprises if two main components, namely direct and diffuse radiation.

Diffuse solar radiation depends upon the evaluation of place and its latitude, the solar altitude the sun's declination, the degree of turbidity, the amount of water vapor present in the atmosphere and cloudiness. Variability in the amount and type of cloud cover is the major factor in determining the ratio of diffuse component of the global radiation at a particular place is important for the design and the assessment of solar energy systems. Therefore, in the absence of measured data, methods were suggested to estimated the diffuse components of the total horizontal radiation. To obtain a rough estimate of monthly average daily diffuse radiation for Quetta (Pakistan), I.A. Raja et al [114] considered a nearby station in Tehran (Iran) where

167 the diffuse radiation is recorded and compounded the monthly

average at daily diffuse radiation from sunshine hours on

the horizontal surface both of Thran and Quetta.

2-5\ Monthly average diffuse solar radiation on a horizontal surface. For the prediction of monthly average diffuse radiation i.e. on a horizontal surface, two different type of correlation

exist : a. Monthly average diffuse radiation, exposed in terms if the fraction of maximum possible sunshine hours and using

extra terrestrial radiation relationship by Iqbal [115] is Hd/H=0.163 + 0.478 n/Nd - 0.655 (n/Nd)2 Where Nd is day length in hours and is the time of bright sunshine hours. b. Monthly average diffuse radiation expressed in terms of cloudiness index Kt=*H/HQ This relation is developed by Klein [116] . H, /H - 1.390 - 4.027Kt + 5.531(Kt)* - 3.108(Kt)3 Many authors [117,118,119,120,121] have treated the estimation of monthly average diffuse radiation as a function of clearness index but the most commonly used correlations are by page [122] and labeled [123] .

Page [116] developed a correlation between daily global

radiation and its diffuse component for location between

40°N and 40°S and suggested the following relationship. Hd/H = 1.00 - 1.13 Kt The same parameters are suggested by Iqbal [123] in his correlation Hd/H = 0.958 - 0.982 Kfc Quetta is situation at latitude 35°68'N and altitude

1799m. The variation of diffuse solar radiation on

horizontal surface at Quetta it is obvious that there is an agreement in the estimated values obtained by Klein [116]

Page [122] and Iqbal [123] , and that two peaks for diffuse

component of solar radiation in horizontal surface are

observed. The profile of the peak is more pronounces during

months of April and August.

2 average diffuse solar radiation on inclined surface. The knowledge of horizontal global radiation is

required to predict the efficiency and performance of a solar collector. A solar collector absorbs solar radiation for various orientations with respect to horizontal positions. The orientation of the collector would indeed

depend on latitude, declination angle and on solar tracking

mechanism. In this paper, we have over-tracking mechanism.

In this paper, we have over-simplified the problem by only considering the geometrical orientation which is indeed

helpful and beneficial in designing green houses, solar ponds etc. The tilted surface of the solar collector sees

scattered and reflected radiations from the ground.

Estimation of the diffuse is made for Quetta assuming the

isotropic distribution for diffuse solar radiation over the

IM whole of the visible sky hemisphere. We obtained a relation from Liu and Jorden [124] which is of the form Hdi /Hdo = (1 + cos©)/2 - cos* 0/2 where Hdÿ is the diffuse solar radiation in inclined surface Hdo the diffuse solar radiation on a horizontal surface, 0 is the tilt or inclination angle.

The ratio of the diffuse solar radiation on inclined surface to that on a horizontal value Hdo is calculated for vertical orientation (0°- 90°) from which the diffuse radiation values are almost 50% less than what is obtained for horizontal surface.

The correlation proposed by Lie and Jordan and developed by Klein for an estimate of monthly daily diffuse radiation is found better summer and winter.

The correlation proposed by page [122] are in good agreement with Klein [116] . Estimation from clearness index for monthly daily diffuse radiation is more reliable for Quetta. In order to establish reliable correlation, measurements of diffuse radiation over a long period are required. 2-7. Direct and Diffuse Radiation: Monthly Variation: A large variation in the intensities of direct and diffuse radiation due to cloudiness have been observed. The intensity of direct radiation is determined by the amount of water vapors, dust particles, ozone etc. in the atmosphere.

The plot in Fig. ( £) ) shows the trend of percentage variation of direct and diffuse radiation. The peak value

no of the months of November, December and January are quite appreciable. The percentage of diffuse radiation contributing to total radiation is quite low for winter months (bright clear sky) and attains a attains a peak value of 42-43% in the month of July-August which is also confirmed with the low values of KT and high values of Hd/H , (Firoz et. al. 1981 b) . The bright clear picture of the sky condition at Quetta throughout the year, with the exception of July-August, is very promising and encouraging and is very much in favour of solar energy application and efficient utilization.

Relationship between Monthly Average Daily Diffuse and

Monthly Average daily total radiation:

The relation between the monthly average daily diffuse and monthly average daily global radiation for Karachi is worked out and is shown in Fig. (£) . The plot between Hd/H and H/HQ applies well to the correlation developed by Liu and Jordan (1960) . from this figure, it can be concluded that even during the monsoon months the percentage of diffuse radiation does not exceed 50% while for the rest of the year KT values are quite high. The minimum value of KT during the year is 0.47 which indicates that even for worst sky conditions the availability of global solar radiation from extraterrestrial radiation is about 47%, whereas the maximum available total

nt 0.6_

i i

4 ••S'- 1

X Calculated] from is 0,4 _ : . Liu and Jordan Curve X) IS ; : i O -H ! 4-> X I ; •3 - : : 2 ' : o l O *1 ! : o : f -a : : o) 0 2 - j • 01 . L ! O M 1 •H Q . I

I ry t

! I •

0.0 i i 0.3 0.4 0.6 •i 0.8

Clearness Index (Kÿ)

Fig 3.]ÿ. Plot ol clearness index against diffuse to global ratio, for Qne/Usy ' solar radiation is above 65% for the months of December- January.

2-9. Annual Variation of the Monthly Mean Global Solar Radiation:

The variation of monthly average global solar radiation are shown in Table : 3v8 and it is seen that there is no drastic variation from year to year data. This data obtained

from P.M.D. (Quetta) depicts the fact that value of monthly average of global solar radiation ranges from about MJm-2 to 21 MJm-2 . The exception values being 16.72 (1969), 17.43 (1978), 17.50 (1983) and 17.96MJm'2 (1984). This is encouraging from solar energy application point

of view. (j fis available solar insolation shows a remarkable consistency for a period of almost 30 years. The consistency of available solar insolation is shown in Fig. ( f- ) for Quetta.

J.jo. Monthly Average Hourly Global and Diffuse Solar Radiation

at Quetta.

Long term average values of the instantaneous (or hourly)

global and diffuse solar irridiance on a horizontal surface

is often required in many solar energy applications . However, there are only few locations where this hourly data is

available. Deriving this from the corresponding daily values

is somewhat easier because of the existence of certain

empirical relationships between the hourly and the daily

I 7* total radiation for the different hours of the day.The first attempt to analyze the hourly radiation data was made by

Whiller (1956) and Hottel and Whiller (1958) who used the data of widely separated location to obtain the curves of rt (the ratio of hourly to daily global solar radiation) vs the sunset hour angle for each hour from 9 a.m. to 3 p.m. following the earlier work of Whiller (1956) , a theoretical method for deriving the mean hourly diffuse solar radiation from the mean daily total, was developed by Liu and Jordan (1960) . Making the assumption that the atmospheric transmission be constant throughut the day and independent of solar altitude, the theoretical expression deduced by them was of the form: rd = CQS

Liu and Jordan's curves, Collares-Periera and Rabl (1979) developed an analytical expression for the ratio r in terms of the sunset hour angle, given as below:

/7$ (rt = _a_ ( a + b cos4* ) COS - cos s— ) sintlQ ~2n cos 8 3iOS where coefficients a and b are given by a = 0.409 + 0.5016 sin ( - 60 ) b = 0.661 - 0.4767 sin ( «*>s - 60 ) The graph to work out the hourly data from daily values is given in Fig. ( Ct ) and is valid for the mean values of the hour pairs around the solar noon. This has been tested and verified for many locations of the world, with positive results. These plots are valid for long term averages of cloudy weather and for individual days of clear skies. They are plotted in terms of A, 1M, 2 A. 3A, AY and 5Y hours around solar noon. The time is taken at mid hours because the measured data are recorded as the hour ends . The assumption that the transmission factor of global radiation does not vary appreciably during a day, leads us to consider the symmetry of solar radiation around solar noon. Thus taking the solar noon as our reference point, the hour pairs during a day, assuming constant transmission in Table. ( " ) .

In this table the hour angle increases by 15 degrees during one hour. The hourly radiations are further subdivided into the diffused and beam component of radiation. The sum of beam and diffuse component should be equal to the hourly total radiation and the sum of all the hourly total radiation should be equal to the monthly average daily total radiation on horizontal surface. 2-/1 Estimated and Observed Hourly Solar Radiation Data for

Quetta.

Estimation of hourly radiation data, from its daily

value have long been established. Liu and Jordan (1960) outlined a procedure for getting the hourly global radiation

from the daily total value H, as stated before. In order to get a better estimate of the hourly solar radiation data for

Quetta, the Liu and Jordan method was employed. The value of

H were obtained from the source mentioned earlier. Table ( rL ) shows the estimated values of monthly average, hourly global solar radiation at Quetta as obtained from eqn. {2-f) . All the radiation are in Wm-2 In Fig. (£) the measured monthly average hourly global solar radiation

for each hour pair is plotted for the four representative

months Jan, April, July and October. 2..12' Measured Average Hourly Solar Radiation Data: Hourly solar radiation for Karachi, on horizontal

surface was measured, using a portable solar radiometer and

solar cell pyronometer (manufacturer) ; Ms Wather Measure

Corporation, Sacremento, California, U.S.A) . A complete one

year data for the year 1985 and scattered data in a span of

three to four years were taken by these instruments. These

instruments were calibrated after every month and it was found that the accuracy is good enough within ± 1% . The measured average hourly global solar radiation of the year

1985 is given in Table ( C ) where the daily data was summed ns- TABLE : 3 . £ AVERA6E HOURLY VALUES OF GLOBAL SOLAR RADIATION AT PAKISTAN (LATTITUDE 24°.54'N ) MEASURED DATA ON HORIZONTAL SURFACE

TIKE 6-7 7-8 8-9 9-10 10-11 11-12 12-1 1-2 2-3 3-4 4- 5 Sf6 TOTAL .TOTAL MONTHS our P.M.D data data

JAN 20.6 121.3 310.2 480.4 519.8 676.1 685.0 595.0 446.3 294.4 109.7 16.4 15.68 14.16

FEB 27.6 170.0 353.9 560.1 6e0.0 738.5 741.3 672.4 .571.8 343.1 163.6 23.8 18.23 18.52

MAR 45.3 230.9 427.5 605.2 730.2 821.1 810.7 724.3 582.6 425.0 217.4 39.0 20.47 19.09

APR 113.8 295.6 492.1 678.3 791.4 877.1 855.3 782.0 666.9 468.9 288.3 110.5 23.20 23.71

MAY 124.6 333. C 518.4 637.9 703.7 837.2 849.1 748.5 629.0 516.6 312.7 111.6 23.08 22.80

JUN. 148.2 304.6 511.2 618.8 712.6 810.1 821.0 715.4 599.6 503.1 294.8 122.5 22.28 22.20

JUL 126.1 258.3 414.1 532.0 621.7 711.6 698.4 630.2 541.1 410.0 240.7 112.2 19.12 18.80

AUG 93.2 241.6 410.2 524.6 612.8 650.0 638.7 598.8 514.1 424.3 250.2 87.5 18.25 17.06

SEP 68.7 241.3 445.8 590.0 708.2 780.3 767.7 690.5 601.3 434.6 222.7 53.5 20.27 20.30

OCT 31.4 176.7 365.0 554.3 701.8 778.6 763.7 695.0 545.4 354.2 168.1 27.8 18.67 17.50

NOV 11.9 117.2 328.5 504.2 611.7 705.6 697.8 621.3 458.7 311.2 101.6 8.7 16.35 14.90

DEC 10.3 97.4 263.1 437.2 590.1 642.6 658.3 560.9 434.6 288.1 99.7 8.1 14. 80 13.63

-2 (ALL RADIATION VALUES ARE IN Wm"2,OUR DATA IS SUMMED UP IN MJtn and P.M.D DATA IS IN MJm“2)

•P.M.D. Pakistan Meteorological Department.

I TABLE: C

HOUR ANGLE HOUR PAIR ( DEGREES) A.M. P.M.

0.00 12.00 noon 12.00 noon 7.50 11-12 12-1 22.50 10-11 1-2

37.50 9-10 2-3

52.50 8-9 3-4 .6 7.50 7- 8 4-5 82.50 6- 7 5-6 97.50 5- 6 6-7 LEGEND 000000 Jan x * a x Apr Jul V-V—S—9 Oct

3.0 —|

2.5 _

\ / S \ / v 2.0 _

A \ \ 1.5 __ t // \ / \ / \ 1.0_ / \ / 1/ \ V

0. 5__

0 . 0 1 I I I I 1 i 1 6 7 8 9 10 11 Noon 1 2 3 4 5 6 Time I'ii? 3. C*>. Monthly Average Hourly Solar Radiation at QMJ&V. (Estimated data)

4 TABLE :3 Cl . AVERAGE HOURLY VALUES OF GLOBAL SOLAR RADIATION AT PAKISTAN (LATTITUDE 24°.54’ N) ESTIMATED DATA ON HORIZONTAL SURFACE TIME 6-7 7-8 8-9 9-10 10-11 : -12 12-1 1-2 2-3 3-4 4-5 5-6 6-7 MONTHS

JAN 21.83 118.8 306.8 472.6 605-3 688.2 688. 2 605.3 472.6 306.8 118.8 21.83 FEB 29. B1 165.0 364.8 534.8 665.0 749.9 749.9 665.0 534.8 364.8 165.0 29.ei MAR 58.32 233.8 438.6 613.6 748.5 834.7 834.7 748.5 613.6 438.6 233.6 58.32 APR 93.42 280.5 480.1 642.3 767 .3 854.6 854.6 767.3 642.3 480.1 260.5 93.42 MAY 130.20 325.6 507.7 657.8 781.4 853.0 853.0 781.4 657. e 507.7 325.6130.22 32. JUN 138.20 . 314.4 490.0 628.2 735.2 804.0 804.0 735.2 628.2 490.0 314.0 138.2 31. JUL 116.6 265.3 414.0 530.9 621.0 690.2 690.2 621.0 530.9 414.0 265.3 116.6 31. AUG 89.0 232.4 386.1 504.7 604.1 668.0 668.0 604.1 504.7 386.1 232.4 89.0 14. SEP 65.7 224.7 416.5 575.0 696.5 773.6 773.6 696.5 575.0 416.5 224.7 65.7 OCT 37.3 187.1 390.0 572.1 711.0 786.1 „ 786.1 711.0 572.1 390.0 187.1 37.3 NOV 13.8 129.0 322.5 497.8 631.6 714.5 714.5 631.8 497.8 322.5 129.0 13.8 DEC 12.43 108.0 282.5 448.8 581.8 652.8 652.8 581.8 448.8 282.5 108.0 12.43

(ALL RADIATION VALUES ARE IN W:n 2) c .2 0.20— O DATA OF PAKISTAN 4i Experimental ratio of the •H hourly total irridiance to •o the daily total irridiance 2 0.18_

4J O 0.16 O >. o •H o o a 0.14_ o c p° o o •H h m 0.12_ •H _1H '0 o fO o o o K o o

' < 0. 10 o n) 4J— 0 H _ O O n— 3k f-i* 0.08— ° u O 73 OO O o 4*1 u 0.06- >- o 0 n 0. 04_ 5 x 0° o o 0.02 6*i o o

0 I 1 I I 8 9 10 11 12 13 14 15 16 T 60 75 90 105 120

Sunset Hour Angle ,u>g ,Degrees 4 Fig 3. H f TABLE: 3. •MEASURED AVERAGE HOURLY VALUFS OF GLOBAL SOLAR RADIATION ON HORIZONTAL SURFACE AT ( LATTITUDE : 24°.OH ' N) - RATIO OF AVERAGE HOURLY TO AVERAGE DAILY RATIO Time 6-7 7-8 8-9 9-10 10-11 11-12 12-1 1-2 2-3 3-4 4-5 5-6 MONTHS

JAN 0.004 0.027 0.071 C.110 0.136 0.155 0.157 0.137 0.102 0.067 0.025 0.0037 FEB 0.005 0.033 0.070 0.111 0.134 0.146 0.147 0.133 0.113 0.068 0.032 0.004 MAR 0.008 0.041 0.075 0.107 0.129 0.145 0.143 0.128 0.103 0.075 0.038 0.007- APR 0.017 0.046 0.Q76 0.105 0.123 0 .136 0 .133 0.122 0.104 C.073 0.045 C.Ol 7 MAY 0.019 0.052 0.081 0.099 0.119 0.131 0.133 0.117 0.098 0.080 0.049 0.017 JUN 0.024 0.049 0.083 0.100 0.115 0.131 0.133 0.116 0.097 0.081 0.047 0.020 JUL 0.238 0.048 0.078 0.100 0.117 0.134 0.132 0.116 0.102 0.077 0.046 0.021 AUG 0.018 0.047 0.081 0.1C4 0.121 0.129 0.126 0.118 0.101 0.084 0.049 0.017 SEP 0.012 0.043 0.079 0.105 0.126 0.139 0.137 0.123 0.107 0.077 0.040 0.009 OCT 0.006 0.034 0.070 0.107 0.136 0.150 0.148 0.134 G.1C5 0.068 0.032 0.005 NOV 0.002 0.026 0.072 0.111 0.135 0.156 0.154 0.137 0.110 0.068 0.022 0.002 DEC 0.002 0.023 0.064 0.106 0.144 0.157 0.161 0.137 0.106 0.070 0.024 0.002 FROM MEASURED DATA OI‘

11-12

<> „ or' O' 15 “V * ~ <\ / 's

--- 9-10

10 _ \

<#> 8-9 a) rr> +Jc aiu t-i 5 ai - "O ©—

N --- *V 7-8 •s •s >"" 3ÿ "©

6-7 0 1 i 1 1 I I 1 J r M A M J JL A S O N D Months

Fly Percentage frequency distribution of Monthly 3.J Average Hourly global solar radiation (%) TABLE: PERCENTAGE HOURLY GLOBAL SOLAR RADIATION DATA AVAILABLE DURING A DAY FOR 3-7 DIFFERENT MONTHS OF THF YFAR. _

MONTHS Early morning From 9 a.m. to 3.p.m. Late afternoon (% available insolation)

1.SUMMER M= 25% , Apr ,28%,May~30% Mar: 7 5% , Apr :7 2 . 3% /May:70% Mar , Apr , May, Jun -30% ,Sep=26% Jun: 70% .Sep: 74% Jun , Sep.

2. MONSOON

Jul , Aug. Jul:30%, Aug:30% Jul:70%# Aug: 70%

3. WINTER Jan; 20% rFeb:21. 6% Jan:80%,Feb.78.4% Jan , Feb, Oct , Oct : 22% , Nov:19. 7% Oct.:78% , Nov:80 .3% Nov, Dec. Dec:19% Dec:81%. MAY

3.0

2.5 DECEMBER

7 2.0 _ T3 c* I E 2 c 0 . •i-( 1.5 _ •p m •P T3 ro cZ _ o t/3 >i

o X „ _ 0.5 -

! I 6 8 .10 Noon 2 4

Fig 3.jf Time Comparison of houriv solar radiation for Summer and winter months at Pakistan up for a particular month to give us the monthly average.

The measured data seems to be in very good agreement with

the predicted values estimated through the Liu and Jordan method. This is shown in Fig. (H) . Also given in Table (r ) is the variation of the percentage of hourly global solar

radiation contributing to the daily total. This has been shown graphically in Fig. (X). From the table ( -£• ) it is evident that on the average about 75 percent of available energy is received from 9 a.m. to 3 p.m. (i.e. about six

hours) , whereas early morning and late afternoon values have

a very little share in the daily total. The Table ( L) shows the breakup of the available 100 percent solar radiation

with respect to the hour pairs. The average percentage is

obtained from the 12 month day for each pair: If we take the season wise breakup of the average

hourly solar radiation in terms of the percentage

availability, the categorisation can be made according to

the scheme given in Table ((f). Shown in Fig. (-X) is the

comparative display of the availability of hourly global

solar radiation for summer moths May and the winter months

December. The difference in the availability

of radiation is very much obvious.

2. )3. Estimation of Monthly Average Diffuse Solar Radiation From Clearness Index:

Liu and Jordan (1960) page (1961) Iqbal (1979),

Collares Periera & Rabl (1979) Erbs et . al. (1980),

\lb D.P.Lalas et . al . (1987), Neuwirth (1980), Barbaro et . al .

(1980) and many others have treated the estimation of monthly average diffuse radiation Hd as a function of its daily total value H, i.e. ( H*/rV- In these relations '

Liu & Jordan (1960) had developed a correlation, which were mathematically expressed by Klien (1977) in the following form: _ 3 Kd = Hd/H 1.39 - 4.027 KT + 5.531 K'2 - 3.108 KT where "H is the monthly average global solar radiation HQ is the monthly average extraterrestrial radiation, and KT = H/Hÿ is the clearness index. Page (1961) developed a relationship between Kd and and suggested the equation; Kd = Hd/H = 1.00 -1.13 K . . C&£) Iqbal (1979) in his correlation employed the same parameters to suggest the following relation; /

I 77 and

K = Hd/Ho = a6 + a7 (Kÿ.) + a8 (Kt)2 .. 130 2- .Estimate of Monthly Average Diffuse Solar Radiation from Sunshine Hours.

Another approach to estimate the diffuse soar

radiation is the use of one of the most important weather

parameter, the relative sunshine hours, n/N, where n is the

number of actual sunshine hours, and N is the average day

length, taken at the mid of each month.

The correlation employed by Stanhill (1966) takes the following form Kd = Hd/H = 0.964 - 0.786 ( Ti/N ) ...an while Iqbal (1978), proposed a very simple relationship Kd = Hd/H - .1- (n/N) ....

second-order were developed for Quetta. This is given below as i

where is the regression constants and Hd/H* and Hd/Hÿ is the fraction of diffuse to global and diffuse to extraterrestrial radiation, respectively.

17& 2. ii. Calculation from Monthly Average Hourly Data: In order to compute the radiation incident on a

tilted surface it is necessary to start with the hourly

direct and diffuse radiation. If it is not available, it can

be estimated from the daily global radiation using a method given a Liu and Jordan (1960) . The average of the hourly values of direct

radiation is calculated as the difference between the

average hourly global radiation and diffuse radiation.

Knowing the average hourly direct an diffuse components,

Duffie and Beckman's (1974) method is employed, which

provides the relationship between the radiation incident on

a slope and that on a horizontal surface. A south-facing surface is considered as being the most common orientation in the northern hemisphere. The factor rb which relates the direct solar radiation Ib, s for a tilted surface to the

solar radiation on horizontal surface Ib, o' is given as rb “ Ib,sÿIb,o = cos(4> -s)cosf cos h + sin ($-s)sin£

cos + cos S cos h + sin t sin <5 where + is the latitude ( for Quetta + = 24° .54' N) , s is the tilt angle, h is the hour angle and is the declination . The monthly average hourly insolation on a tilted surface is composed of the following components,

It,s = Ib,s + Id, s + Ir,s • US’)

179 Where and are the hourly direct and diffuse Ib, s Id i s radiation on a tilted surface and Ir,s is the value of reflected radiation incident upon a tilted surface. The more generalized expression due to each component is written as

It , s " rb Jb,o + 1+cos-§- *d, o + 1-cos So? (/ T 2 a— to or

, s = rb Ib, o + I+cos s *d, o + 1-cos s S’ 1t,o 2. X. •• 1%)

In the above equation, p is the ground reflection with values ranging from 0.2 (no snow) to 0.7 (ground covered with snow) . A detailed compilation of the surface albedo for various reflecting surface, as worked out by Hunn and

Calafell (1977). For Quetta, p is taken to be 0.2

In equation ( ) , Ib,o' Id,o and It , o are the hourly direct, diffuse and global solar radiation on a horizontal surface. Equation {}£) is valid for any instant.

However considering on hour as a short enough period, rÿ is evaluated at the mid point of the hour angle h.

Given the average hourly values of the global radiation for all the hourly intervals into which a day can be divided, the total radiation Ht,s can be obtained by summing the hourly radiation for each hour from sunrise to sunset on this surface. The value of the hour angle at sunrise or sunset for a south-facing surface tilted at an 12o cos hg = - tan (4 - s) tanS-- .. a?) Calculation From Monthly Average Daily Data:

The method developed by Liu and Jordan (1962) of estimating the average daily radiation for each month on a tilted south-facing surface is described in Klien's review paper (1977) . It is also extended to calculate the radiation for off -south orientation (east or west of south) . The average daily radiation on a tilted surface is given as HT = RH = RKTH’0 U3> where R is the ratio of the daily average radiation on a tilted surface to that on a horizontal surface for each month. R can be estimated by considering individually the direct, diffuse and reflected components of radiation incident on the tilted surface. Assuming diffuse and reflected radiation to be isotropic, Liu and Jordan (1962) suggest R as equal to R = (1- Hd/H) Rb + Hd/H (1+cos s) /2 + ?(l-cos s ) /2 . 09 where "Hd is the monthly average daily diffuse radiation, is the ratio of the average beam radiation on tilted surface to that on the horizontal surface, s is the tilt angle from the horizontal and p is the ground reflectance, usually taken to be 0.2 when there is no snow. From a surface facing directly southward Rb cos(4>-s) cos* sin ws + (n/180)u,s sin (ÿ-sjsin*- SS. cos 4> cos $ sin + (n/180) <*>s sin 4 sinS where s is the sunset hour angle for tilted surface given as 1*1 (A s = min ( ws arc cos (-tan (4>-s) tan ) . . Ufo) when dealing with the monthly averages, declination can be

chosen for an average day of the month. Klein (1977) has

suggested the average day to be chosen for each month, at which the solar declination, £ in equation ( *f0) should be computed . As measurement of diffuse radiation are not

available for many locations, it can be estimated from the average daily global radiation using the method given by Liu

& Jordan, expressed mathematically by Klien (1977) and the one given by Page (1961) . The ratio Hÿ/H is related to KT values (clearness index) as follows:

1.390 - 4.027 tCj, + 5.531 K 2 3.108 ICj. 3 (Liu & = r - Jordan)HV«

H'/r 1.00 - 1.13 ICp (page) Page's relationship gives a more accurate estimate of the diffuse radiation fraction, which results in a better

computation of R. 2.1h Method of Calculation: The monthly average daily total radiation on an inclined surface "HT can be expressed as Rp =ÿ RH ... (*/> where H is the monthly average radiation on a horizontal surface, Rÿ is the ratio of the monthly average daily radiation on a tilted surface to that on a horizontal surface. This is ratio R can be estimated if we know the beam, diffuse and reflected radiation incidention tilted surface. With the assumption that diffuse and reflected radiations are isotropic, R can be written as

=ÿ ( ) {l-cos s) (l- Hd/H)R b + TTd/H l + cos s + 2. ? 2.

where is the monthly average daily diffuse radiation, Rb is the ratio of average beam radiations on tilted surface to that on horizontal surface, s is the tilt angle and p the ground reflectance, taken to be 0.2 for Quetta. In the absence of measured value of diffuse radiations, estimated values were obtained using the relationships developed by Liu and Jordan (I960) and Klien

(1977) as stated in the previous section. Page's (1961) method is also employed for the estimation of diffuse solar radiation. An equation for Rb has been developed by Llien (1977) in his review paper for a surface of any tilt and azimuth, and is given as (cos s sin 6 sin X<*>'sr ) (n/180) _ sin s cos/ ) ( gr ) (n/180) + (cos 4 cosj cos s) ( sin ioss sin sr * + v sin'/ sr '

2 (cos 4 cos 6 sin wB + ( n/180) ( sin 4 sin 5* ) in the above equation “i is the surface azimuth angle, 4* is m of place (for Quetta, 24. 54'N), the attitude the $ = Q - is the solar declination which can be calculated as stated in the previous sections by using Cooper (1969) equation. A = 23.5 sin {360 ( 284 + n ) } 365 and Wgs and <ÿrs are sunset and sunrise hour angles on the tilted surface which in turn are expressed as ;

Usr = - min u>s , arcos { (AB + / - B2 + 1 ) } ( t) Lhj-)

for Y > 0

u) ss Z min , arcos { (AB - /A2 - Bz -t- ~i ) } (*Xrl)

and

for Y < 0

w ss ~ min , arcos { (AB + J A2 - B2 + l ) } i (A»;

IZf to calculate sr and ss , A and B can be evaluated from the relation: A = Cos A + sin A {sin v tan s) tan x and B - tan A { cos 6 sin d) tan x sin x tan s

"min" means the smaller of the two values in the angle which is bracket, s in the bracket is the sunset hours expressed as {% - cos-1 ( -tan 4> tan A ) } Thus a detailed calculation procedure has to be adopted in order to calculate the off -south oriented surface inclined for various tilt angles . For due south oriented azimuth angle x is zero, whereas it changes by 15° for every hours. For the orientation west of south the azimuth angle is assumed to be negative while for east of south orientation, azimuth angle is assumed to be negative while for east of south orientation, azimuth angle t,is positive.

For the purpose of computation of monthly average global solar radiation incident on inclined surfaces, the azimuth angle y were chose to be varying in a step of 15°, east or west of south, starting from 15° to 75°. The tilt or inclination angles of the flat surface was increased in a step of 10°, from 10° to 90°. A computer programme in BASIC language was written to cover the variation of azimuth angle y and inclination angles s, for the months of a year. IBS' The results of the computational work regarding the

global solar radiation incident on surface with different

inclinations and various azimuth for the twelve months o the

year, have been analyzed and many important conclusions are drawn f rom it . 2/8. On The Choice of Proper Inclination and Orientation at

Quetta.

It is always desirable to increase the amount of incoming flux of solar radiation incident on a flat surface, at any particular location. This can be done by inclining

the receiving surface or giving it a particular orientation.

This may be beneficial and may not be. So one has to

carefully and critically calculate the related parameters

and its variation during a year, before making any decision

for Quetta, we had done it so. The results given in the preceding section critically needs an assessment for the

justification of the choice of proper inclination and

azimuth angle for different months of a year. For this

purpose we first consider the effect of orientation,

secondly the annual total radiation and its variation. This

will give ourselves enough information for deciding the

things in the right direction.

2 -Hi. Correlation of Average Diffuse, Beam and Global Solar Radiation With Hours of Bright Sunshine.

The total solar radiation {beam plus diffuse) is the most important factor in such applications as

/& climatology and agriculture. Beam radiation is important in some industrial applications such as solar furnaces and other solar energy concentrating devices. Whereas diffuse

radiation data is required for energy related problems associated with building research etc.

The solar radiation measuring network usually

record global solar radiation on horizontal surface. This data is mostly available on daily and hourly basis. These

radiation values on horizontal surface are then used to compute the insolation on an inclined surface. In developing and underdeveloped countries, the situation regarding solar

radiation recording stations is not encouraging at all. In

Pakistan, only five stations, Karachi, Lahore, Multan,

Quetta and Peshawar record global solar radiation on horizontal surface. Therefore for the other places, one has

to depend on the different empirical relationships which have been suggested so far for estimation purpose, employing different climatological parameters. The measured data of global solar radiation is available, but the data on diffuse solar radiation is not available at all, since no station in the country records it. To assess the availability and variation of diffuse solar radiation, one relies and depends on the estimated value, for a particular location under these circumstances, the need was to develop correlation of global, beam and diffuse radiation with hours of bright sunshine, for Quetta Iqbal (1979) has carried out similar studies for Montreal, Toronto and Goose Bay in m Canada and S.Barbaro et. al. (1981) for diffuse radiation for Italian Stations Palermo, k Macerata and Genova.

m 2.2.0. Optimum Tilt Angle and Orientation For Solar Collectors in QUETTA.

Many investigators have studied this problem

from different points of view. Kern and Harris (139)

obtained the optimum tilt angle as a function of

latitude, weather data,f and the character of the energy

demand. They recommended the latitude angle as the best iSt, tilt angle. Ladsaongikav and Parikh {' ’ found that the

tilt angle is a function of latitude and declination

angles. They also observed that the effect of tilt is

more pronounced for places away from the equator, and that it is more advantageous to tilt the surfaces with the horizontal more during autumn and winter than summer. Garg and Gupta (fS.6 ) concluded that, for average

winter and summer performance, the optimum tilts are

•a O (latitude angle»£+ 15) and (latitude angle - 15) , respectively and for year round performance, the best tilt is 0.9 times the latitude angle. Neville (126J examined the maximum solar energy

available to the collector as a function of latitude,

the north-south tilt of the collector from earth surface

and whether the collector tracked the sun or was a fixed

type collector (fixed in the north-south direction) . It was concluded that the fixed type collector had about

50% the efficiency of the collector tracking the sun.

Hamdan and Majeed ( ) estimated the solar energy

available to an inclined flat plate collector by

I?? predicting the values of the conversion factor, R, which

is the ratio of total solar radiation on a tilted surface

to that on a horizontal surface. They presented this

factor graphically as a function of collector tilt, hour in the day, and month of the year. Villarrubia et al . (/a 7) calculated the monthly averages of hourly irradiance upon surfaces tilted

towards the south in Barcelona, Spain by using global and diffuse average hourly solar irradiance on a horizontal surface. They determined the optimum slopes corresponding to maximum incident energy, calculated from the annual average of daily solar radiation. Willmott { //j? ) developed a numerical climatic model for computing total solar irradiance on the surface of a flat plate collector, positioned at any tilt and azimuth. Cooper (/- ,

) studied the influence of inclination since it affects the heat losses due to variation in natural convection in the space between the plates. The results indicate that there is a continual reduction in the top loss coefficient up to inclination of 90. He also recommended that, in the total design of a large system, the influence of angle of inclination should be consider.

The aforementioned papers clearly indicate that, usually, the flat plate collector is oriented north-south to avoid the complicated task of tracking the sun and that the inclination of the solar collector to the horizontly influences the irradiance on that tilted

)9o surface. Liu and Jordan ( iZ-n) considered the radiation on

the tilted surace to be made up of three components; and

solar radiation diffusely reflected from the ground. The

total solar radiation on the tilted surface for an hour

is then the sum of three terms

I = Ib Rb +ld (l+cosÿJ) /2+p(lb+Id ) (I-cosÿ j2, The geometric factor, Rb is the ratio of beam radiation on the tilted surface to that on a horizontal surface. For an hour, it is given by ( <5/ ) Rb =rbT/rb = cos 0 / cos & , - lv?) where cos Q~ is given by — cos Q - = sin d sin cosyS - sin & cos

_ 2 = [yyj

Liu and Jordan suggest values of diffuse ground

reflectance of 0.2 when there is no snow and 0.7 when

there is fresh snow cover. The beam and diffuse radiations on a horizontal surface, Ib and Id are determined by using the standard clear sky conditions presented by HJottel ( / 3/ ) and Liu and Jordan ( O-' ) repectively. The clear sky hour's beam radiation on a horizontal surface, i;> given by (/££)

/?/ Icb =lm cos ~(*°J where Ion and 2*b are calculated from the following equations = I,c [ / f 0.033 cos (360n/365) ] -(?/ ) Vb = a0 + a, -($2.) The constants a0 , av and k for the standard clear atmosphere with 23 km visibility are found from a0 aj and k‘ , which are given for altitudes less than 2.5km by

( /S2 ) -y- X aQ = 0.4237 0.00821 ( 6-A) -tW JL aÿ = 0.5055 0.00595 (6.5-A) -(5V X k = 0.2711 + 0.01858 (2.5-A) -- Lss-j where A is the altitude of the ob server in Kilometers.

Correction factors are applied to aol alt and k to allow for changes in climate types. The correction factors rD = a0/a0 , rx = aÿa* and r* = k/k, are given in Table 1.

It is also necessary to estimate the clear sky diffuse radiation on a horizontal surface to get the total radiation. Liu and Jordan ( ljÿ ) developed an empirical relationship between the transission coefficient for beam and diffuse radiation for clear sky = 0.2710 - 0.2939ZV - where C' d is Icd/I0( the ratio of clear sky diffuse radiation to the extra-terrestrial radiation on a horizontal plane. The clear sky hour's diffuse radiation

!9l- on a horizontal surface is given by

led = 7*d cos#, ( 5?) Equation (£7) is used to estimate— diffuse cldear sky radiation, which can then be added to the beam radiation

predicted by Hottell's method, eq. (*f

day total radiation. These calculations can be repeated

for each hour of the day, based on the midpoints of the

hours , to obtain the standard clear day's radiation. Substituting eqs. ( % , (ÿ and (J>) in eq. ($£) , we obtain I = Ion (rb COs£+rd COS*, (t + COByfl ) /2+p( ) cos 0 . (I-cosÿ) /2] . -

total radiation on a flat plate solar collector, (dlM ) r = 0 is found, and hence the optimum tilt angle is given by

{cos/(cos<5 cosÿ- sin [fÿ P opt = tan-1 sinÿ> & cosÿ)/ (l-pjcos*, /2f -j*cos © /2 + sin +cos $ cos p cos to ]} (SO)

Substituting yÿin (5£) » the maximum total radiation on a flat plae solar collector with optimum tilt angle is f ound .

To get the optimum orientation, which gives the

maximum total radiation on a concentrating solar

collector (or a flat plate collector ) tracking the sun,

(dl,. /d/ ) = 0 is found, and hence the optimum surface azimuth angle ( jorientation) is given by .1 i = tan [sin / (sin cos i0 tan cos )] of>t - £ m Substituting 7ÿ. in eq. ($8), and getting (dlr/ dÿ) = 0, the optimum tilt angle is found at that optimum orientation which gives the maximum radiation on the collector surface.

Optimum tilt angle calculation for a location in

Quetta is used for the conversion of total solar radiation on an inclined surfaces have been obtained, considering different orientations i.e. the latitude of the place, j

Models suggested by Liu and Jordan (1J4) and that of Klien (!}'/) are calculated and found that Liu and

Jordan (1J4) more suitable for orientation of flat-plate solar collectors facing south with respect to the place of the latitude. The 60° tilt surface receives an irradiations is hot season i.e. 1.7 to 2.0 times the irradiation on a surface with the tilt equal to latitude.

The isotropic model (l-'f) is also used to estimate the total radiation for South facing surfaces of various tilt angles and parameters. A comparison has been made between the Liu and Jordan and Hay models and the results are presented in Table.

The knowledge of solar radiation incident on a tilt plane is very imortant to engineers designing different thermal devices for conversion and useful applications of solar energy. Therefore, it is a pre- lOif requisite to estimate the effect of orientation receiving solar radiation falling upon the sloping surface, we employed this approach to optimise the utilization of flat-plate colectors because they absorb both direct and diffuse components of solar radiation. Some authors, and Hay (1ÿ*5) Liu & Joran (ljf//) , Norris (1ÿ7) Klien (Uÿ) have successfully described the total solar radiation on tilt surfaces from measurements on a horizontal surface. There are several methods to compute global radiation on tilted surface for the measurement daily global and diffuse radiation on a horizontal surface but Liu and Jordan (1ÿ4) and Hay (l>/7,' have proposed methods for the computation of daily solar insolation on atilted surface which is discussed here. We know that the angular correction for dirct radiation is quite simple, but for diffuse components it depends on different factors i.e. cloudB, spatial distritution and atmospheric components that determines scattering.

Therefore, the behaviour of flat-plate collectors at different orientations at the ground or other surfaces could be approximated to a source of different diffuse radiation equivalent to the sky. Under these conditions the total solar radiation on a tilted surface. H, H, t H, . Hr —-((ÿ') where Hb and Hs are direct and diffuse components of the total solar radiation and Hr is the ground reflected

I9S- radiation. The daily beam radiation received on a tilted surface can be expressed as Hb = (H - Hd )Rb —{£*) where H is the monthly mean daily global radiation on a horizontal surface and the Rb is calculated as cos (ÿ>-s) cosS sin + (TT /180)<«>O sin -s) sinÿ Rb cos cos 5 sin + (TT /180) sin sin

No. ( £>3) by considering the radiation on a tilted surface to be made up of the diret and diffuse radiation and the solar radiation reflected from the ground (Hb Hd and H ) using the following equation relationship (£tj) Ht = -HOL)ZL + H p(t+ces?j/z t I+£**&)/2

Measurements and Calculation.

Global radiation data measured over a period of two years is used in the present work. The pyranometer is installed at a height of 2 meter from the ground and calibrations were checked regularly. Firstly Rb, Hb and Hd are calculated for various

fM tilt angles and values are given in table. The total solar radiation on tilt surfacs are computed from equation 1 and listed in table. Considering orientations with the help of different correlations. Estimated and measured monthly meanb daily global radiation on inclined surface at different angles are presented in table (k)

The result presented in table given a comparison between the estimated data calculated by the most important and familiar models {!$/) of the same order. However, the difference as we observed between these two models are quite small, so any one of these models can be used for

Quetta station. But the Liu and Jordan is favoured for computing monthly mean daily global radiation on tilted surfaces because of its simplicity. In Quetta valley the winter months are Nov. -Feb. and the summer months are Jun.-Aug, Generally the winter months are more clloudy and most of the rainfall occurs; while summer months cloud free or very nearly so. Considering the table we noted that the tilt angle 30o is the best angle for . O collecting solar radiatins during Apr. -Aug, where has been found to have a maximum radiation during Sep.- Mar. for cooling purposes £*3(0-

in January

. 5 +15

+ 45

r'' \ -X \ .. G_ v.. \ X Cast of so \ W sc of \ \ —-- • so \ V \V75 \ \ \ \ \ \ \ \ V15 \ \ \ \ \ \ o \ ). 5- \ V \ \ \ \ -45 \ \ \ V V \ \ \ V75 \ \ \ \ \ \ 1 1 i 0 20 40 60 80 100 Inclination Angle (Degrees)

Fig 5.7(a) for off-south orientation of inclined surface at , Pak istan April 1. 5 _

East of toutl West of soutl

1.0 A

Rb \X \

w\ \ \ + 75 0.5 \ \ X \ + 45 \\\ \ \\ \ \ V \ +15 S \ \ \ -15 \\\ \ \ \ -75 s \-45 \ I i J 0 20 40 60 80 100

Inclination Angle ( Degrees )

Fig 5.7(b) for off-south orientation of inclined surface at , Pakistan 1.5 July

-East of soutl West of soutl

1.0- V\ N. \

Rb \\\\

0.5 V\ + 75 N o\ ScW \\\ \v '+4 5 \\\ -15 +15 \Y\ I I -45XV5\ I 20 40 60 80 100 Inclination Angle (Degrees)

I’ig 5.7(c) Rÿ for ofl;-south orientation of inclined surface at , Pakistan October 1. 5 _

East of South West of South

___ o-o 1. 0 _ — X X so N X +15 \ \ V \ \ \ \ + 45 \ \ \ o 75 \ \ \ + Rb \ \ \ \ \ 0.5 _ \ \ 'o \ \ \ \ \ \ \ \ \ -15 \ \ \ V \ -45 \ -75 \ \ I I 1 \ I J 0 20 40 60 80 100

Inclination Angle (Degrees) Fig 5. 7 (d) Hfa for off-south Orientation of Inclined surface at , Pakistan 74k ik) Total Solar radiation (H,) received on Inclined surfaces at Quetta (MJ/m2) for 1990-1991.

S=0 S=+15 S-0+30 S»®+45 S - o s-m-15 S-0-30 S-U-45 S-60° Jan 12.62 20.69 12.80 6,48 28.91 34.27 6.58 32.96 3.71 Feb 16.69 23.96 9.88 10.05 29.59 32.48 10.05 26.84 5.53 Mar 17,84 21.48 18.08 13.25 23.21 44,71 19.68 15.52 9.20 Apr 23.37 24.40 23.71 20.14 23.03 19.83 15.17 10.78 12.28 May 25.36 23.91 25.00 24.26 20.21 15.12 11.07 7.86 21.17 June 25.44 22.96 25.06 25.08 17.25 13.72 9.62 7.34 23.80 July 22.16 20.43 21.06 21.86 17.09 13.26 9.77 7.75 28.05 Aug 22.05 21.73 22.35 20.27 19.71 16.00 12.13 8.82 16. M2 Sep 21.56 24.30 21.56 17.16 22.87 22.52 18.54 13.70 12.21 Oct 18.24 23.94 16.50 12.17 26.12 28.91 26.85 22.20 7.46 Nov 14.15 22.32 14.15 7.56 29.25 34.27 34.98 31.50 4.10 Dec 11.98 20.65 12.14 5.75 29.60 35.90 33.94 30.49 6.93 of it*, fcvzfot- Values ofj for various tilt angles at Quetta

S=0 S=+15 S-0+30 S-0+45 S - ® S-®-15 S-O-30 S-0-45 S 60° Jan 1.00 1.38 1.01 0.56 1.68 0.57 1.81 0.66 0.31 Feb 1.00 1.26 0.67 0.68 1.43 1.51 0.68 1.35 0.54 Mar 1.00 1.14 1.04 0.79 1.20 1.79 1.08 0.90 0.74 Apr 1.00 1.03 1.01 0.90 0.99 0.89 0.72 0.51 0.88 May 1.00 0.96 0.99 0.97 0.85 0.67 0.48 0.24 0.94 June 1.00 0.93 0.99 1.01 0.79 0.60 0.37 0.11 1.20 July 1.00 0.94 0.99 0.99 0.81 0.63 0.40 0.15 0.81 Aug 1.00 0.99 1.01 0.94 0.92 0.78 0.59 0.36 0.64 Sep 1.00 1.08 1.00 0.85 1.10 1.03 0.90 0.71 0.41 Oct 1.00 1.20 1.01 0.73 1.32 1.35 1.29 1.14 0.16 Nov 1.00 1.34 1.00 0.60 1.59 1.72 1.74 1.64 0.64 Dec 1.00 1.42 1.01 0.52 1.75 1.95 1.89 1.78 forthsu*

tor fob Hir Apr Hay June My Aug Sep Oct Nov Dec i •, t-M fi.fr /.0 /Ml II.// 10.0 7.6/ 10.10 10.10 9.6! /.If. /./! .i .i 6.!W/ 6.79 6.IQ 6.1/ 10.16 11.30 8.10 9.XI 10.60 9.X) 6.63 6.A/ ;'ii () 6.80 5.26 9.6/ 10.4b n.Q3 6. Zb 10.6b 9.48 6.47 /.43 7,V/

b.r* t-.t‘ * 6./J 10. /A 11 .HI ItUfi 10.61 0.3' 8,t

I; t>, Oh •;.// 6.4U 9. Ml 9.6V 12.20 10. /u 9.16 10.73 7.68 /.XI 6. 90

$• t ./'• 6.00 11.20 12.0 4. :<>; 9.40 9.60 9.60 6.30 fi.6*6 t.rQ 'Mi 3.19 10.no 10.8/ 11.40 9.3/ 7.29 9.90 9.67 7,8V 6, bO

t -V 6.61 7.60 6.77 10.09 11.60 4.40 10.26 10.00 9.6! 8.16 7.00 6.10 6.81 9.33 10.68 10.67 in. IQ 10.16 10.00 10.36 8.8/ 8.13 i. b.t-1 5.3/ 6.66 10.57 9.45 9.02 10.60 10.85 10.4/ 10.9/ 9./1 6.4/ ftppfivAtx u; Tetei MmtVy Smskht Mem et Q—tts.

dm Mir Apr Nay June July Aug Sep Oct Nov Per •>, yl2.il 1/7.0 21/.n 22b.0 m.o M.O 2:i8.0 313.0 m.o 296.0 21b.O 239M • . -J /'M.O M.O 192.0 248.0 31b.0 M.O 280.9 28b./ 318.0 288.0 m.o tbS.O 7.1.u n',:i M.O 287.0 324.0 .171.0 I93.Q rw.2 29b.1 202.0 223.0 717.' i. 1(4,71 188.8 247.0 330.0 iSt’.O 318.0 338J1 789.0 789.0 777.0 . •*- - 188j, 171.0 166.0 287.0 30-1.0 366.0 :o/.n 284.0 322.0 m.o 217.0 183.0 m.u 188.0 746.0 346.0 389.0 JVI.O 7)3.0 286.0 296.(1 746.0 2117.0 '* ; 71*71 761.0 301 . 0 177.0 313.0 >89.0 72t>.0 297.0 300.0 734.0 203M -\u .4 .0 734.0 263.0 313.0 316.0 Ml'.il 316.0 303.0 29b.0 248.0 707.0

) , \ 3,t'. \%f* m 738.0 211.0 M . 0 331.0 .120.0 0 318.0 300.0 321.0 2t*'.U 282.0 i; ’4.11 149.0 207.0 217.0 293.0 270.8 378.8 336.2 314.0 340. U 291.3 262.7

» Pt-fPM/xCM) Sky Conditions and Radiations at Quetta.

J*m I ol> Kirch April Hdv •June* July Aupust Sep Or.L Muv IVi 13. 16 H.IQ I/.44 77.01 77.04 77.80 I 0.44 18.1/ 70.33 18.34 14.78 17.98 II 70% 76.0/ 31.60 36.87 41.18 40.63 38.7? 31.87 78.76 77.61 l‘J./7

II ii 0.63 0.60 O.SS 0.60 0.67 0.66 0.48 0.48 0.60 0.66 0.61 II.oo - K, IIJIMI 4.60 r» % 7.76 8. 18 9.11 9 44 0.40 8.0.1 7.40 l».8fl 4.81 4.04 H. 0|1>.il II .14 0.41 0.4? 0.3/ 0.40 0.41 0.40 0.40 0.3/ 0.3? 0.14 0.31 Mil

IqlM I 0.41 0.3? 0.3? 0.37 0.34 0.33 0.76 0 . ?4 0.38 0.44 0.4? ll.4*i Ull h|hiil 0.71 0.73 0.73 0.?2 0.73 0.73 0.73 0.73 0.?? 0.?| 0.7] 0.71 H/H l(|lhil 8.60 8.43 10. 18 13.83 13.10 13.46 0.96 0.74 17.84 17.46 0.46 8.01 n INI I). M» 0.60 0.68 0.63 0.60 0.60 n.6i 0.61 0.63 0.68 0.66 0.69 brpM(X c £) Direct and Diffuse Radiation

H«ilhs . I.in feh March Aprt 1 Hay June July August Sep Oct Nov IVH

it* ft.hft 8.43 IQ. IB 13.83 13.&3 13.4b 0.0b 0.24 12.84 12.47 9.45 H.94 lijh.il MO 4.SO !*.% /.?!» 8. |0 0. IU 0.44 0.40 ft. 02 /.Ml b.Bfi 4.83 4.04 h?re*AtxCC)

HoiiLh Jan Fet> March Apr!1 May v)une July August bet> Oct Nov Oct; K. 0.63 0.65 0.56 0.60 0.57 0.66 0.48 0.48 0.60 0.65 0.63 0.60 V II. 0.21 0.23 0.23 0.22 0.23 0.23 0.23 0.23 0.22 0.21 0.21 11.21 MEAN MONTHLY GLOBAL RADIATION TEN YEARS PER DAY AVERAGE QUETTA Mj/m2 30 -

25

20

15

10 i i 1I J FMAMJ JASOND J FMAMJ JASOND J FMAMJ JASOND

1967-1976

1 MEAN MONTHLY GLOBAL RADIATION 30 YEARS PER DAY AVERAGE QUETTA MJ/m2 30

25 - T'*: 20 -

15 -

m. 10 -

5 -

r ' 0 T I i : I Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec H1957-1986 MEAN MONTHLY GLOBAL RADIATION TEN YEAR PER DAY AVERAGE QUETTA

35 MJ/m2

30

25

20

15

10 J FMAMJ JASOND J FMAMJ J ASOND J FMAMJ JASOND

-•-1957-1966 -*-1977-1986 CHAPTER-II (B)

Solar Heating/Cooling Systems for Buildings.

Energy conscious design requires a method or

tool for estimating the thermal performance of building designs. So far simulation has made its mark on novel and experimental projects, particularly passive solar. Distinct from sophisticated models, a simplified simulation model, called Exacaliburr, has been developed. This model which has been subjected to validation studies [139,140], attempts to combine the practical advantages of the conventional methods, with the scientific rigor available from simulation. The essence of the simplification is to use a lumped parameter building representation that reduces a multi node problem to a two-node problem. This makes it possible to perform simulations on an IBM PC.

The model [141] is a second order, five parameter model described by the following equations.

CadT±/ dt = Q- (T± -TW ) /R± - (T± " TQ ) R-L CW dTw /dt = -(Tw - Ti)/Ri ~ (Tw - T0 )/R0 .... lit) The five parameters are: 1. Rl , lightweight heat loss path 2. Ri , heat path from building interior to structure

-mas®— 3. Cw , equivalent structural mass; 4 . Ro , heat path from structural mass to outside;

198 5- ca , equivalent air mass Q is the heat delivered to the space and includes the solar and casual gain contribution. TQ is the external temperature, the internal air temperature, and Tw the structural mass temperature.

The solar gains are deduced from the diffuse and

direct radiation components that are stored in a meteorological database with the external temperature and

solar azimuth and elevation. The meteorological data are for

the year 1965-1966 at Kew Observatory, U.K. which is believed to be a good representative year for southern

England. The model operates a maintained temperature mode

during occupied periods when Ti is held constant, unless

driven upwards by solar gains. The required input of heat,

Q, to the space is then determined. During the unoccupied - J periods, the plant heat input will be known (being maximum

in the preheat and zero during the cool down period) and so Tjÿ is determined. The solutions for these most are found analytically and have the form. Tÿ (t) = a + bt + c expf-S-ÿ t) + d exp(-S t) (preheat/cool down modes) . . . < Q ( t) = a' + b' t + c' exp ( -S ' t ) ( maintained mode ) < '&) In these solutions the constants a,c,d,a', and c' depend on

the five parameters and embody the initial values of the tmeperature, heating, and meteorological field. The b, b' terms that re

linear in time, reflect the linear interpolation of the

external temperature and any casual gains between time grid point. S1 is response time of the air and furnishing and and S2 are the structural response times during the preheat/cool down and maintained temperature modes, respectively . 2-21 Passive Solar, Low-Energy Residences with Transparent insulation:

The factors considered are; design construction,

occupation, comfort, energy characteristics, performance of

the Transparent Insulation, including staining by pollution,

overall energy consumption, cost effectiveness practical

aspects and important lessons learned.

The main design criteria were: - passive solar orientation and room arrangement . - the use of transparent insulation in a LEGIS south facade . - high insulation over a dense construction.

- mixed active and passive control for comfort. - low energy lighting. - obtaining casual gains, including air-to-air hear recovery. south roof orientation for eventual solar water heaters . - aesthetic appeal. The development of Transparent Insulation (T) is

2oo best followed in the regular proceedings of the workshops

published by the Franklin Company. Figure explains the

characteristics of the LEGIS wall incorporating the TI material. The design is that of the Fraunhofer Institute for

Solar Energy, Freiburg [142,143].

2l2rThermal performance of the TI construction. We have investigated performance criteria.

Effective U value: The conventional thermal conductance U

value, of a wall is defined assuming no significant absorbed

radiation heat flux and symmetrical heat transfer

characteristics. The building standard U value for an outside wall is 0.45 W/m(m2 K) . For a transparent wall, we define the effective thermal conductance Ueff as: ueff = 3w*j I -Ta,jÿ • • • (>D

Where; Tr is room temperature; Ta is outside ambient temperature, and qw is the net heat flux out of (positive) or into (negative) the room averaged for each of n days . On this basis, and averaging over monthly intervals, there has been a negative Ueff value for every month of the year. With the blinds operating, ueff - 0.9 W/m* value and solar capture efficiency: The daily net heat flux from the room to

the outside environment can be analysed as:

<3i = ud (Tr - Ta> ' e Gv + Ss (72) •

20! so,

(Qi - qs)/Tr ' Ta) + ud - e [Gv/ 1 where; Txr is daily average room air temperature. Ta is outside daily average ambient air temperature. is the conventional thermal conductance, U value

measured in the dark. Gr is the global vertical daily insolation on the outside of the TI wall.

e is defined by the equation as an efficiency of solar capture. <3s is the daily net heat flux into the room from heat stored in the wall .

We estimated qs as an approximation from the night-time envelope of the plot of internal south wall temperature with time,- it is a relatively small quantity and could be ignored.

Fig. (121) is a plot of equation (?2) for 28 days in

iox ’ i

1 1

B B a B B

N * 0 0

rs B £ a £ » • B a S B -1 (2 a i a % X> a E i £ a -2 a

-3 i j x r -3 0 1 2 3 4 5 6 7 Gv/(Tabs-Ta): W/(m2.K) Intercept : Uti= 0.7 W/(m2JC) Slope: ta = 05 1* Graph for cqn ( 1 considering ihc wall as a solar collocior February 1991 and 1992, from which the intercept gives Ud (0.59 W/(m*K), and the slope gives e{0.43).

Our values on a real building compare sensibly with measurements [144] on a similar LEGIS cladding using identical new TI material on a calibrated test cell [U=0.54 W/ (m2 K) , e = 0 .40] . TI wall as a solar collector: Taking just the measurements at the outside dense wall surface behind the TI, eqn (ÿ ) has the from of the Hottel-Whillier equation

for conventional collectors:

= UTI (Tabs "= Ta) - taGv • • • C?4 > so

(<5abs/ = UTI - « Wv / (Tabs ' Tla> I • •

qabs is the heat flux through the heat flux maton the outer wall surface.

UTI is defined by the equation as the thermal conductance of the TI "cover": Tabs is the outer wall temperature. T is the combined transmittance of the outer glass, TI and backing sheet. a is the absorbance of the wall

Fig. (122) is a graph of eqn CJ5) for the same 28 days in February 1991 and 1992 . The intercept gives UTI = 0.70 W/{M*K), and the product (ta) = 0.50.

2cJ \ 1 H a

K 0 a

o 0 a a * E 0 -i a H a 0 » • a B a 0 -2 u- H s cr “3 -3

-4 I i X i i i —4 0 1 2 3 4 5 6 7 8 9 10 Gv/(Tr-Ta) : W/(m2.K) Intercept : Ud = 0.59(W/m2.K) Slope:e = -0.43 JÿGraph for cqn{ÿ.The average ordinate is . the intcrvepi i% the dart ( value (0.59 W /nr K ), and the slope c(0.43 ) is the solar fraction. Annual Collectible Energy of a Two-Axis Tracking Flat

Plate Solar Collector.

With the advent of increasing interest in

photovoltaic systems, there are a number of advantages of

using a two-axis flat-plate collector. Sine the tracking system is generally much cheaper than the collector panel,

such a mode permits the incident solar radiation to be

collected more efficiently. Incidence angle effects are minimized and moreover, contrary to concentrating

collectors, such a mode enable both the diffuse and beam

components of solar radiation to be collected. We have made

the following specific assumptions in this study:

1. Since the correlation we seek to develop would apply to relatively large array of collectors, the ground cover ratio ($= Ac /Ag ) has to be included. We have assumed a constant, though realistic, value of 4> - 0.25 throughout .Thus the shading effects occurring among the collectors during certain periods of the day are included, during which period no beam irradiance reaches the ground. Hence the area by which the beam irradiances received is either Ac cos0 or As cos0z . 2. Though it is presently known that an isotropic sky model [145] or solar radiation underestimates radiation incident on fixed flat-plate collector [146] it is uncertain what this degree of underestimation would be, if at all, for a two-axis tracking flat- plate collector.

Poy- Consequently, we have simply assumed an isotropic sky model in this study.

3. A ground reflectance value of 0.2 has been assumed for all months and all locations.

4. Utilization of energy occurs at constant efficiency

and the transient effects have been neglected.

5. The collector operates year round and it energy is

entirely utilized.

6. The instantaneous tilt angle of the collector plane or the solar zenith angle on a horizontal plane ©2 is the one that corresponds to the midpoint of a particular hour. 7. The irradiance values are considered as constant

values during a particular hour and those of the hours of sunset and sunrise are corresponding fractional

values of that particular hour.

As the instantaneous tilt angle on the collector plane is equal to the solar zenith angle ©z on a horizontal plane, the hourly irradiance on the collector plane could be written as 1 min {cos® !/ÿ cos©; cp = Ibn nn < } + 1/2 nn Kd {(1+ cosez}ld+ pI(l-cos©2) } . . . Ui) we make the following correction for the incidence angle Icp = Ibn nn min{cose, l/4> cos©} +1/2 nn K2 {l2(l+cos©z ) +pl (l-cos©2)}

Jor effect on the collector plane for diffuse and ground- reflected radiation components only (since beam radiation is always at normal incidence) . The mean incidence angle modifier (K ) for isotopically diffuse and ground reflected radiation is *?? Kd = K (©) cos© sin© d© . . . { ) where K [146] is the instantaneous incidence angle modifier for optical efficiency on the collector plane as proposed by [147] .

K (©) 1 2.02xl0"5©2 + 4.69 = - w x 10'7 ©3 - 1.8 x 10"8 ©4 where © is the instantaneous incidence angle on the collector plane (degrees) .

Hour-by-hour values are obtained using equn ( ) .

Annual collectible energy n the collector plane as a function of the critical radiation JQ (lc = 0, 0.1, 0.2,...., 0.9 kW/m2 ) are computed as follows: + (Icp Jc > ... (» Ac fR nn year Qd (Ic) annual collectible energy on the collector plane is simulated from actual data as a function of Ic (GJ) . Note: The + sign signifies that the summation of each component is done only when the argument is positive.

These simulated values are then curve-fitted with a polynomial of the form: J)3 Qp-ilc-l— S3 {B± (2 j-1) + B± , 2 jI bn — - j ”1 Ac fR nn i=l j=l X L Ici-1 • • &0) 2s> where Qp(Ic) = annual collectible energy as a function of *c (GJ) ; Ibn - yearly mean normal beam irradiance summed over all hours and average over the set of (365x12) (kW/m* ) ;

(rad) L = latitude angle of the location ; and Bk, m - coefficients to be evaluated.

Note: as the collector receives diffuse radiation, the latitude dependence of the polynomial is considered.

Finally, the coefficients m of the polynomial are evaluated by minimizing the sum of squared differences between (Ic) and Qp(Ic) , the sum runing over all locations and over the threshold values of Ic = o, 0.1, 0.2... . 0.9 kW/me . This leads to 18 simulataneous linear equations, the solution of which yield the coefficients

Bk, nr The following correlation for the annual collectivle energy of a flat plate tracking about two exes is suggested by Attalage and T .A. Reddy [14?] . A A Qp (Ic) = (+8.524+13.849 I bn) +(-19.387+0.000 I bn)L Ac FR nn + (+12.928+3.755 IAbn)L*x{ (-15.104+6.475 l"bn) +(-2.916 - 0.023 IAbn)L + (+18.544-39.276 IAbn)L,}l A x{ (+3 .527-43.138 I bn) + (37.783+57.295 I*bn} L

+ (-46.569-0.083 l"bn)LM I2 c . . . («D A in case I bn is not known, we suggest that the linear correlation proposed by YL.€eUj[\AY\ be used, nemely A A 1 bn = " 0.34 + 1.37 K (Si; A where K 1. E ii 365.25 year Ho

Xol Analytical and numerical approaches for the predesign of central solar heating plants with seasonal storge (CSHPSS) systems are compared [ f

Central solar heating plants with seasonal storage

(abbreviated CASHPSS) provide a heating technology with a high solar fraction in a northern high climate. During the last ten years, these systems have unergone a significant improvement in both technical and economic performance. The pre-commuercialization of CSHPSS are already under way and it is expecte that the number of systems, that today is in order of 35, will increase [ if# ) . The SOLCHIPS [my] program represents a different approach in which the optimum sizing is directly solved analytically without using the traditional numerical route. The modelling is based on yearly system and storge energy balance equations and on some observed unique features of a seasonal storage system. The program is planned for predesign of seasonal storage solar heting systems and includes all necessary sub-systems and components. The input required has been kept simple and at minimum and may be used also by non-professionals. Santamouris et al [1501 report the finding of a

monitoring campaign in 186 office buildings in Greece. The

present study provides useful information for the efficient energy planning as well as appropriate design and equipment selection, in office buildings.

The following information is required for each

buildings

1. General information about the occupants and the

building; this include the name, address legal

status, owner, the construction yer, the number

of stories, the heated surface and volume, and

the daily occupation profile.

2. General and specific information about the y building

envelope; for each side of the building, the

orientation, the vicinity with heated or

unheated space, and the type of glazing and

shading were recorded. A detailed description of each exterior building element, walls, ceiling, and floor was also included.

3. Information about the heating cooling, and

lighting systm. Here, the type, the power, and

the operational profile was recorded. The

duration of the heating and cooling period, the

control type and the set points, as well as the maintenance policy were also noted.

2x>9 4. Information about the office equipment: The type and the power of the used office equipment was

recorded in each building. Also, information about specific appliances like water heaters, ref rigrators, fans, and pumps were

collected .

5. The energy consumption of the building: The

quantity of every type of fuel and the consumed electricity in each building was recorded. The

exact data were from the monthly electricity and

fule consumption official receipts kept in each building. In parallel with the standard forms, a specific questionaire was designed in order to collect information about the thermal comfort and the indoor air quality inside the office buildings.

We must also follow the above mentioned pre¬ requisites to suggest appropriate designing parameters of buildings.

2/0 CHAPTER-III.

Conclusions & suggestions for Future Work.

We infer from our present study the following conclusions . The correlation proposed by Liu and Jordanfi3ÿj and developed by Klein//3(,) for an estimate of monthly daily diffuse radiation, for Quetta over a period of twenty two years i.e. from 1970-1991, is found better.

The correlations proposed by Page (./.s') are in good agreement with Klein { lllfj. Estimation from clearness index for monthly daily diffuse radiation is more reliable for Quetta (lyAl.

Estimation of mean global solar radiations in Pakistan

over a period of two decades i.e. from 1958 to

1979 indicates that Quetta on an average, receives the best solar radiation of about 763 J/m /sec and that solar radiation intercepted on the earth's surface during the summer season (i .e.June-September) is maximum and during autumn (i.e. October-NOvember) is minimum . Klein (j;4) relationship for the estimation of diffuse

and direct component of solar radiation in found

suitable for Quetta in a recent study by A. U. Durrani

et al

The mean monthly sunshine hours are correlated

with the monthly mean values of the solar radiation by

2)1 using the equation. H = HQ t a + b (n/N) ] which shows that solar radiation for Quetta varies from 3.6 to 7.65 KWh/m* (if?) This reflects that the calculation of global solar radiation from shushine hours is in good agreement with estimated valuesÿ".?; .

We found modelling procedures of Jainÿ/ÿiS) quite satisfactory for estimation of diffuse radiation at

Quett particularly from view point of environment conscious architecture.

Our critical analysis and calculations for optimum tilt angle and orientation for solar collectorsÿ-,?) are in good agreement with analysis of Morcos (10) .

We, in Quetta found that a 60° tilt surface of a flat plate collector facing south receives about 1.7 to 2.0 times the maximum irradiation on a surface with the tilt equal to latitude especially in summer (IC'i ) whereas for the same tilt maximum solar energy round the year is received. The comparison of models by Liu and Jordan (Cÿj and by Hay (IJ.Lf) for faces of various tilt angles and parameters of collectors indicates no particular difference.

Energy conscious design requires a method for estimating thermal performance of building designs.

The building energy estimation of Murdoch and Penman

(B) is found suitable in our climatic conditions at

2 1 2 Quetta. We recommend the use of transparent insulation (TI) in

building designs at Quetta particularly in a LEGIS

south facade because our south facing collectos at a

60° tilt receive maximum solar radiations throughout

the year and that the south roof orientation for solar

water heaters in a passive solar building design.

The seasonal storage solar heating and cooing systems

are recommended for building designs at Quetta.

The use of a two-axis tracking flat plate solar

collector is recommended for Quetta. We found the

correlation for annual collectible energy of a two

axis tacking flat-plate solar collector by Attalage

and Reddy (//'") in agreement with our estimated shear

energy received at various tilt angles.

Operational modes of solar heating and cooling systems

( /{,/) are recommended for Quetta. For designing and construction of a residential solar

heating and cooling systems, analysis of Ward and Lof (lbS-Jis found suitable. Both active and passive solar heating/cooling systems are recommened for Quetta with environmental and climatic considerations. Our critical review i.e. in Chapter- I has already suggested conditions on which architectural design of buildings and residences at

Quetta could be easily tested and employed in future

213 town planning.

Suggestions for Future Work.

In order to establish reliable correlation, measurements of diffuse radiation and sunshine hours over a long period are required.

The performance of a flat plate collector is highly influenced by its orientation and its angle of tilt with the horizontal . Therefore, both fixed plate colletors having prevision of tilting at varius engles and a two-axis tracking collector preferably of concentrating type should be used to monitor intercepted solar energy, heat transfer through various liquids and that their influences both on active and passive solar heating/cooling systems.

Both active and passive solar heating/cooling systems could be selected on the basis of our critical review. Experimental work with residential and official building designs should be under taken on proto- type systems with all facilities.

Fast simulation of various kind of data as mentioned, is our critical review, and, in results and discussions, should be employed to test various models, correlations and theories so that a proper experimental modeling produce for solar architectural design may be explored. REFERENCES.

1. R.B.Pope and W.P.Schimmel. The Solar Community and the Carcaded Energy Concept Applie to Single House and a Small Subdivision-A Status Report, SLA-73-0357. Sandia Lboratories, Albuquerque, New Mexico, May(1973).

2. W.H.McCulloch et al.. The Solar Community-Energy for Residential Heating Cooling and Electric Power, SLA-74-0091. Sandia Laboraories, Albuquerque, New Mexico, April (1974).

3. C.E.Robertson and J.H.Banker, A Photographic Technique to Determine the Apparent EnergyDistribution of the Solar Aureole, SL-74-0090. Sandia Laboratories, Albuquerque, New Mexico, March (1974).

4. R.A. Tyboul and G.O.G. Lof, Solar house heating. Natural Res. J. 10 (2) (April 1970).

5. J.A. Duffie, Private communication.

6. H.Yeh, Conservation and better utilization of electric power by means of thermal anergy storage and solar heating. Final Report National Sciene Foundation Research Project No.Gl-27976 (July 1973).

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