Basics of

Practical Heat Load Calculation

Webinar 30 April 2020

Vikram Murthy ASHRAE Mumbai Chapter Sessions

►Basics of Psychrometrics ►All about Heat ►Practical Heat Load (Cooling Load) Calculation

( Using the E 20 , CLTD - Cooling Load Temperature Difference Method ) Psychrometric basics Psychrometrics ► A hundred and eighteen years ago, Willis Carrier, developed a method that allows us to visualize two of the variables -- the combination of air temperature and that exist in a space. The tool he developed is called the Psychrometric Chart.

► Psychrometrics, which Willis Carrier developed, is the study of the mixture of dry air and , and is the scientific basis of . Willis Carrier Willis began his first job at the Buffalo Forge Company .

Solving a Problem at the Sackett Wilhelm Lithographing Company in Brooklyn, he formulated the Laws of Psychrometrics . Willis Carrier laid down the Equations of Psychrometrics in 1902 .

The Carrier Company he founded developed the Centrifugal and the Weathermaker, that we call an Air Handling Unit or AHU . Purpose Of Comfort Airconditioning

►To Cool or Heat

►To Dehumidify or Humidify (remove or add moisture)

►To remove odours

►To remove particulate & microbial pollutants Definitions Of Air

► Air is a vital component of our everyday lives. ► Psychrometrics refers to the properties of moist air.

► Dry air ► Moist air

► Moist air and atmospheric air can be considered to mean the same Units

► We work in INCH POUND system of units, IP units.

(The other unit system in use is SI units)

Units of length: ft, inches. Units of area: sq.ft Units of volume: cu.ft.

Weight: pound, lb. Moisture: grains. 7000 grains = 1 lb. Units

► Temperature: Deg F Ice = 32 deg F (0 deg C) ► Boiling water = 212 deg F (100 deg C) Body temp.: = 98.6 deg F ( 37 deg C) Karachi Summer temp = 99 deg F (37.1 deg C) Heat: (sensible and latent) Btu Specific Heat: btu/lb per deg F Specific Heat of dry air: Btu/lb per deg F Specific Heat of water vapour: Btu/lb per deg F W = humidity ratio, lbs of water per pound of dry air Units

► Rate of heat flow: Btu/Hr

1 watt = 3.41 BTU/Hr 1 kW = 3410 BTU/Hr 1 H.P. = 2545 BTU/Hr 1 Ton of = 12,000 BTU/Hr

K value: BTU/Hr/Sq.ft/Inch thickness/deg F U value: BTU/Hr/Sq.ft/deg F

Air quantity: cuft per minute, Cfm Psychrometry

►Air conditioning, by its very name means treating air. ►How would Air behave when it is subjected to cooling, heating, humidifying or de- humidifying processes. ►A study of the properties of Air at normal atmospheric . ►Such a study is what is called Psychrometry. Psychrometry

►Psychrometry is the science of studying the thermodynamic properties of moist air and the use of these properties to analyze conditions and processes involving moist air.

Psychrometry (from the Greek word : psukhros which means cold) , is the study of moist air (which is mostly oxygen, nitrogen and water vapor) and of the changes in its condition. an energy or heat graph

►Any point on the psychrometric chart represents air in a specific condition containing a certain amount of heat. The following can be determined by using a Psychrometric Chart : ►dry-bulb temperature ►wet-bulb temperature ►relative humidity (RH) ►humidity ratio ►specific volume ► temperature ►

Dry Bulb Temperature

►air temperature ►indicated by a thermometer ►measured using a normal thermometer ►degrees (oF) ►an indicator of heat content ►Constant dry bulb temperatures ►appear as vertical lines Dry Bulb Lines

►Any vertical line is a line of constant temperature. ►condition of air represented by any point on this line will have the temperature corresponding to this vertical line. ►the temperature as recorded by a thermometer which is dry. Dry Bulb Temperatures

 Dry-bulb Temperature - The temperature of air as registered by an ordinary thermometer.  The horizontal X-axis denotes dry bulb temperature (DBT) scale.  Vertical lines indicate constant dry bulb temperature.  DBT is the air temperature measured in °C or °F and determined by an ordinary thermometer. Typical DB Line Humidity Ratio / Absolute Humidity

Y-axis indicates humidity ratio or absolute humidity, which is the weight of the water, contained in the air per unit of dry air. This is often expressed as pounds of moisture per pound of dry air. Humidity ratio is found on the vertical, y-axis with lines of constant humidity ratio running horizontally across the chart. Humidity Ratio / Absolute Humidity

 The Y axis shows the water vapor component and is generally shown in lbs of water vapor.  Sometimes the vapor content is also shown in grains of water vapor.  One pound of water vapor =7000 grains of water vapor  Moisture is indicated in either Lbs of water vapor or grains of water vapor, per pound of dry air Typical Absolute Humidity Line Wet Bulb Lines

►There are number of parallel slant lines which are called wet bulb lines. ►temperature of the air as recorded by a thermometer with a wet wick on its bulb. ►air having a certain wet bulb temperature will have a definite heat content although its dry bulb temperature may be anything. Wet Bulb Lines Wet Bulb Temperatures

 Wet Bulb Temperature (WBT) is defined as the temperature at which water, by evaporating

into air, can bring the air W e to saturation at the same t B ul b temperature Li ne  Inherent in this definition is an assumption that no heat is lost or gained by the air. MEASURING THE WET BULB TEMPERATURE

 The wet-bulb thermometer is wrapped in a cotton wick; when the wick is completely wet, swing the thermometer around, and the water evaporating at the wick pulls the wet- bulb thermometer’s temperature down in direct proportion to the water content of the air around it.  The drier the air, the more water evaporates at the wick and the lower the wet-bulb temperature gets MEASURING THE WET BULB TEMPERATURE

 The wet-bulb thermometer tells us the relative humidity-the moisture content of the air compared with how much moisture it can hold.  When the dry- and wet-bulb temperatures are equal it means that the air is holding as much moisture as it possibly can- i.e. air is at 100% relative humidity. Relative Humidity Lines

►When the air contains its maximum moisture content, we call it saturated air. ►when it contains anything less than this maximum limit then it is not saturated air. ►We, therefore, say that such air is 50% saturated or 60% saturated. ►the percentage saturation is "relative humidity" Relative Humidity

 The Condition of Air at Point T is plotted on the chart and its saturated moisture content is then 2 checked  We find that the T 1 saturated condition moisture content is indicated by Point 2  The moisture condition at condition T is indicated by Point 1 Relative Humidity

 The relative Humidity of 2 air at condition T is the ratio of Moisture content T at saturation, to the 1 Moisture condition of air at the specific condition

RH = Specific Moisture value ( Point1) Specific Moisture value ( Point 2 Relative Humidity

 Relative Humidity, is an expression of the moisture content of a given atmosphere as a percentage of the saturation humidity at the same temperature.  The RH lines are shown on the chart Saturation Line

►The curved line on the extreme left-hand side of the chart is what is called the saturation line. ►condition of air represented by any point on this line is said to be saturated air. ►the air is having the maximum possible content in it. It cannot hold any further moisture. Relative Humidity

The air is 100% saturated when the moisture content in the air is at its maximum possible and the saturation line is shown on the chart Dew Point ►The Dew Point is the temperature at which water vapor starts to condense out of the air.

►Move horizontally on the psychrometric chart and read the temperature where you intersect the saturation line.

►It is the moisture content which determines the dew point. Dew Point Dew Point Temperatures

 When air, at a certain dry bulb temperature and relative humidity, is cooled up to saturation condition, from point R to Saturation, it reaches its DEW POINT CONDITION R  occurs on surfaces, which are at or below the dew-point temperature, and which are in contact with the air DEW POINT at condition R Dew Point

► If the dew-point temperature is close to the air temperature, the relative humidity is high. ► if the dew point is well below the air temperature, the relative humidity is low. ► If moisture condensates on a cold bottle from the refrigerator, the dew-point temperature of the air is above the temperature in the refrigerator. ► The Dew Point is given by the saturation line in the psychrometric chart. Enthalpy

►Wet Bulb Lines as lines of constant heat content of air.

►Enthalpy is just another term used in place of "heat content". Enthalpy

►At any temperature there is a limit to the maximum moisture holding capacity of air.

►At higher and higher , the moisture holding capacity at any given temperature becomes less and less.

►The enthalpy of moist and humid air consist of and . ENTHALPY

 Enthalpy (E) is the heat energy content of moist air. It is expressed in Btu per Enthalpy scale pound of dry air and represents the heat energy due to temperature and moisture in the air.  Lines of constant enthalpy run diagonally downward from left to right across the chart ( As shown). Enthalpy

►The enthalpy of moist and humid air includes the;

►enthalpy of the dry air - the sensible heat - and

►the enthalpy of the evaporated water - the latent heat ENTHALPY

 Lines of constant enthalpy and constant wet-bulb are the same on this chart but values are read off separate scales.  For calculating enthalpy at 1 point (R) the enthalpy is read at point 1. The sensible heat 2 component can be read at R point 2, corresponding to the enthalpy of dry air at the same temperature. The remainder, i.e.. 1 - 2, is the latent heat content. Psychrometric Chart SI Applied Psychrometry Sensible Heating

► adding heat to air whereby the entire heat added goes to raise the temperature of the air. ► no change in the moisture content of the air. ► its condition will move on a horizontal line corresponding to its constant moisture content. ► Since heat is being added during such process, its enthalpy also rises. ► during the heating process the wet bulb temperature of the air will also rise ► already seen, it is the wet bulb temperature lines which are identified as constant enthalpy lines. Addition Of Moisture

►if moisture is somehow or the other added to the air without adding any sensible heat, the process would be represented by a vertical line corresponding to its dry bulb temperature. ►the moisture added carries with it the latent heat of vapourisation of water ►the heat content of the air also rises and hence its wet bulb temperature also rises. Evaporative Cooling

►Evaporative cooling is the process by which air is simply subjected to a spray of re- circulated water. Evaporative Cooling

►However, since we do not provide infinite or adequate number of spray banks, the air does not come out 100% saturated, or at 100% humidity. ►we must define some norm for specifying the humidifying efficiency of the air washer. ►Wet bulb depression Wet bulb depression

► Is simply the difference between the actual dry bulb temperature of the air and its wet bulb temperature. ► The smaller this depression, the closer is its condition to the saturation line. ► If this depression is zero, obviously the air is 100% saturated. ► If the depression is more and more, then the relative humidity of the air is less and less. Evaporative cooling (adiabatic cooling) Outside Design Conditions Sensible Heat

►Sensible heat is dry heat causing change in temperature but not in the moisture content.

►Btu/Hr = 1.08 x cfm x delta t Latent Heat

►Latent heat is the heat that when supplied to, or removed from air, there is a change in the moisture content of the air, but the temperature of the air is not changed. ► Btu/Hr = cfm x 0.68 x delta W Enthalpy

►Enthalpy is the thermodynamic term for the heat content of air.

►Btu/Hr = 4.5 x cfm x delta H

► Since air can gain heat with either an increase in temperature or moisture content, the terms sensible heat and latent heat are used to distinguish how air has gained heat. Conduction

► Conduction of heat is the process of heat transfer in solids. ► In buildings, heat is transferred by conduction, mainly by the walls or roof either inwards or outwards. Conduction flow rate through a wall of a given area can be described by the equation :

► QS = A * U * T

► where Q = conduction heat flow rate, in Btu/Hr A = surface area, in square feet U = Conductivity value in Btu/hr/sqft/ deg F T' = temperature difference in deg F

► Convection is the process of transfer of heat in which molecules of cool air absorb heat from a warm surface air, rise, and carry it away. ► Convection heat flow in a building occurs mainly in the interior spaces - within a room, between a gap an air gap in the walls, or roof or within two layers of glass in a window. ► Convection and are both forms of mass flow but convection heat flow takes place mainly in the interiors while infiltration takes place between the building and the outside air. Convection heat

►Btu/Hr = cfm x 1.08 x delta t

►Btu/Hr = cfm x 0.68 x delta W. Radiation

►Radiation is the process of heat flow in electromagnetic waves from a hotter surface to empty space. ►The radiation balance "favors" the cold surface. ►This is the only method of heat transfer which does not require a medium for heat transfer Radiation

►Radiation heat gain in the buildings is considered mainly through the window.

►Qr = A * Sc * Sg ►Sg = solar gain factor of window glass. ►Sc = Solar heat gain correction factor due to shading Transmission

►Heat flows from a higher temperature to a lower temperature. ►heat transmission per hour: ►H = A * U * T ►U is the overall heat transmission coefficient expressed in BTU/Hr/Sq.ft/Deg F temperature difference. ►The product A x U is also called "conductance". Thermal Conductivity of a material, k

►is the heat transmitted through the material expressed as BTU/Hr/Sq.ft/Inch thickness/Deg F temperature difference. ► If k is the conductivity of the material then 1/ k is the resistance "R“ of the material of 1 sq.ft cross section and 1" thickness. ►If the thickness is "t" inches, the resistance becomes (t)/(k) per sq.ft. Thermal Conductivity of a material, K

►If a barrier is made up of, say, three materials having thermal conductivities k1, k2 and k3, the total thermal resistance of the barrier is:

t1/k1 + t2/k2 + t3/k3

Where t1, t2, t3 are the thickness of the barriers. Thermal Resistance is ti/k1 + t2/k2 +t3/k3 Calculating U value

►Outside air film ►Transmission thru the material layers ►Air space. ►Inside air film Thermal conductance of air space.

►Dead space of air as a layer ►Exceeds ¾” thickness ►No reflective insulation surfaces like aluminum foil ►Transmits heat by radiation, convection and conduction.

►Value of a = 1.1 U Value

If "U" is the overall heat transmission of the barrier in BTU/Hr/Sq.ft/deg F then, 1/U ( R ) is the overall thermal resistance of the barrier.

1/U = 1/f1 + t1/k1 + t2/k2 + t3/k3 + 1/fo + 1/a

Therefore,

U = ______1______1/f1 + t1/k1 + t2/k2 + t3/k3 + 1/fo +1/a Typical U values in Btu/hr/sq ft/Deg F

► 8” brick wall with ½” cement plaster both sides 0.35 ► 4” brick wall with ½” cement plaster both sides 0.44 ► 4” brick wall, with ½” and 1” expanded polystyrene 0.24 ► 6” RCC, with ½” plaster both sides 0.65 ► 6” RCC, with ½” plaster + 1 in Mosaic Tile 0.40 ► 4” RCC, ½” plaster both sides 0.71 ► 4” RCC, ½” plaster both sides, 2” thermocole 0.12 ► ¼” or 6 mm glass 1.13 Conversion

► To convert U values from ip Units to SI Units :

Multiply U value in btu/hr.sft.F (IP units) by 5.678 to get U value in W/sqm.K (in SI units) Heat Load Calculation

E 20 Method

► The E 20 method is a reliable method to calculate Peak Cooling Loads . If you calculate instantaneous loads using this method, then, in most cases, this calculation will be reasonably accurate to select correctly sized equipment. (The exceptions are if the Peak occurs under a different set of conditions than calculated ) The E 20 method is a method developed by Carrier.

Many more methods have been developed, including a "heat balance method", where you can calculate hourly loads, not just the instantaneous load at 4 PM. (Hourly Load Calculators like Carrier HAP or Design Builder or Smart energy software use this method that include schedules ) Building Survey

► Collect architect's drawings for the building giving all details and dimensions of walls, floors, windows, etc. If such drawings are not available, then survey the place and get the details.

► Building orientation.

► Windows: Location, size and orientation, whether externally or internally shaded. Building Survey

► Partitions: To non-airconditioned spaces, to kitchens, to toilets.

► Roof construction, light roof, sheet roof, insulation, Medium roof (4" concrete), Hung ceiling (false ceiling), Ceiling ventilation, Ceiling, floor, AC above or not.

► Construction details like thickness of wall, material and layers of construction, type of windows, nature of ceiling, roof, floor below AC or not, orientation, occupancy, lighting load, appliances, etc. Thermal Zoning

► What you get as a drawing, remember, has the space divided as a geometrical space. You would need to map out the space as a thermal space!

What we mean by a thermal space, is that, all like areas, being fed by a single split or packaged or air handling system, and therefore are at the same temperatures, can be clubbed together, for the purposes of heat load.

Simply, if there is a row of 10 cabins, being fed by the same equipment, while geometrically there are 10 spaces, you could treat the entire 10 cabin space as a single thermal space. Thermal Zoning

► if there is a row of 10 cabins, being fed by the same equipment, while geometrically there are 10 spaces, you could treat the entire 10 cabin space as a single thermal space.

Of course, some zones, like the Data Centre or the dining area, would be treated as separate thermal zones, because their inside design conditions are different for the rest of the space.

Zoning is an art, developed by practice. Geometric Zones Thermal Zones Multi-story buildings

► You could treat a multi-storied building as one single thermal zone. In which case we call that a block load. you do just one heat load calculation, to get the block load. Of course, for purposes of air distribution, and equipment selection, you may need to do a load for each zone (say, floors). But the total of all the zonal heat loads will add up to the block load. Typically, in a multi-storied building, there is a ground floor a top floor and many floor in between. Since the load for the ground floor will be difference from the intermediate floors and the top floor (because of say, a basement below), it would be treated as a separate thermal zone. The top floor, similarly, would be exposed to sun, so that would be treated differently. But all intermediate floors, could be identical, and you could do a single heat load for that, and multiply that load by the number of floors. If you add all the loads done above, ground, top, and (A x typical floor), the total would be equivalent to the block load. A Typical Commercial office Plan of HVACR Office for Calculation of Cooling Load Summary of Zones and Areas of Walls and Windows Details of Wall & Glass Areas , Occupancy , Lights & Equipment

Floor Area 5120 sq ft Roof Exposed Area 5120 sq ft North Glass Area 144 sq ft North Wall Area 576 sq ft East Glass Area 192 sq ft East Wall Area 768 sq ft South Glass Area 144 sq ft South Wall Area 576 sq ft West Glass Area 192 sq ft West Wall Area 768 sq ft

Occupancy : 40 persons

Lights : 5124 X 0.2 W/sq ft LED = 1024.8 W

Computers : 200 X 20 = 4000 W The Heat Load Form Profile Room Size Outside Design Conditions

► Outside Design Data:

► Which Station ► What is the Latitude ► What is the Daily range

► Summer, Monsoon, Winter

► Given, DB temp. and WB temp. ► Find Grains from the psychrometric chart. Outside Design Conditions

►The data we use is the ASHRAE Weather Data.

( ASHRAE Handbook of Fundamentals ) “Comfort" variables

►environmental variables ►air temperature ►relative humidity ►air motion ►mean radiant temperature (av.) "clo" value, “met” rate, Inside Design Conditions Summer

►75 deg F DB temperature ►55% R.H. Or 60% RH

►76 deg F DB temperature ►55% R.H. Or 60% RH

►74 deg F to 82 deg F ( 23 deg C to 28 deg C ) ►30% to 70% ASHRAE Comfort Chart Inside Design Conditions ► As per ASHRAE, one would choose 75 deg F and 55 % RH.

Note that with each degree F decrease in inside the load would increase by 10 to 15%.

Usually, we do not go below 50 deg F supply air temperature for comfort applications.

The usual guaranteed inside conditions have a tolerance of + / - 2 deg F, and the Relative humidity has a tolerance of +/- 5% R.H. Outside and Inside Conditions

Outside Condition Inside Condition Design Conditions

HEAT LOAD ESTIMATE

At 4pm Est SUMMER Peak

DB WB RH GR/LB O.A. 99 74 21 88 Room 75 55 70 Diff 24 18 Munters Psychro App Outside Air per person

► (ASHRAE standard 62.1 ) Outside air is provided for oxygen and for maintaining the area under slight positive pressure. In some applications, 100% outside air is required.

cfm / person plus cfm per sq ft Deduct the amount of infiltration directly entering into the room. Add the amount of exhaust, if any, to get the net outside air to use in the heat load. Calculation of air changes, is based on the volume of conditioned space. that means, that the height to be used should be upto the false ceiling, if there is one. Ventilation / Outside Air ( Fresh air ) Load outdoor air supply cooling or fresh air coil supply air

return exhaust air air air

space Fresh air calculations

Lets take an example of an office with an area of 1000 sft having an occupancy of 30 persons

The chart shows that for Office application Cfm / sft is 0.06 and Cfm / person is 5 Fresh air calculations

Lets take an example of our selected office with an area of 5124 sft with an occupancy of 40 persons

The chart shows that for Office application Cfm / person is 5 and Cfm / sft is 0.06

CFM OF FRESH AIR REQUIRED = Cfm/ person* Number of persons +Cfm/ area sft*sft of the space

CFM fresh air for the example = 5*40+0.06*5124 = 507 cfm Sources of Cooling Load Outside Air 3 Sources of Sensible Loads

► Heat flow from solar radiation (sometimes called radiation load).

► Heat flow from warmer surroundings (sometimes called the transmission load and sensible infiltration load).

► Heat flow into the space from energy consuming objects within the space (sometimes called internal loads); these objects usually include:

. People . lighting . Office appliances . Motors . any other energy consuming devices Sensible Gains

►Solar gains ►Transmission gains ►Lights gains ►Equipment/ appliances gains ►People gains ►Outside air gains ►Infiltration gains Solar and Transmission Gains

► The sun's heat can get into a building in one of two ways -- through glass and through walls and roof.

1. Solar gains through glass is absorbed instantaneously in the room. This is in addition to the conducted heat passed by the glass.

► 2. Transmission gains through glass, walls, floors, ceilings and roofs. Sunlit Surfaces

sun rays solar angle changes throughout the day Glass

►Remember, glass is responsible for BOTH:

►Solar gains.

►Transmission gains. Lat 20 Deg N Solar Gain Tthrough Ordinary Glass Btu/hr/Sq ft Sash Area O Latitude 20 Deg N Solar Gain Through Ordinary Glass Solar gain equation

► Solar Gain:

► Area x Solar Heat Gain x Overall Glass Factor = Btu/Hr

► A x Sg x Sf = q Shading Of Glass

Venetian Alternate Blinds are Shading , popularly Include used to tinted Shade the glass, Space and exterior Reduce sun Fins / gain Awnings Shading Factors for Solar Heat Gain Through Glass Effect of orientation and time

► Effect of Orientation and time on solar gain. Glass facing East peaks in July - august at 10 am . Glass facing the South shows the greatest load at noon, and is lower before and after noon. Also, it is maximum in December. Glass on the West is the reverse of East. It peaks at 4 pm, and is max,. in July. Glass on the North and any shaded glass all day gets some solar heat that is reflected by dust. Of course, this is very small as compared to direct sunlight. Solar Gain Factor

► Solar gain factor is 1.0 for clear single-paned glass.

► Solar gain may be reduced by using:

► Double paned glass (insulating glass) ► Vacuum or gas – filled, Argon, Krypton. ► Heat absorbing glass (Low e glass), (Low emissivity glass) ► Tinted glass Outside shading devices ► Inside shading devices Solar Gain Solar Gains Transmission gain equations

► Area x (Equivalent) Temp. Diff. x U value = Btu/Hr

► A x ETD x U = q (For walls and roofs)

► A x Temp.Diff. x U = q (For other transmission gains)

► walls, for roofs and correction to ETD Equivalent Temperature Walls in Deg F Equivalent Temperatures Roof in Deg F

Corrections to Equivalent Temperature Deg F

Why ETD value and not Temp.Diff?

►Walls and roofs have capacity to “store” thermal energy.

►Called “thermal storage.”

►Depending on the type of construction, there is usually a time lag of from two to ten hours before this heat reaches the room. ETD values depend on:

► latitude (based on 40 deg N) (Approximately correct for 20 deg N and 30 deg N latitude too). Exposure, N,S,E,W,NE,NW etc.

► Weight of wall or roof, lbs/sft, (10lbs/sft to 80 lbs/sft)

► Wall colour (Correction normally not used, but formula exists in the ► Carrier System Design Manual, if required to be used). 4" brick = light construction. 6" brick = medium construction 8" brick = heavy construction. 4" RCC = medium construction. 6" RCC = heavy construction. Basis of ETD values

► Outside DB at 95 deg F , and room at 80 deg F. ► Daily range: 20 deg F daily range, and for 40 deg N latitude

► Based on 24 hour operation.

► Dark-coloured walls.

► Refer Correction to ETD for walls and roofs Transmission Gain Thru ceilings, floors, glass, partitions. ► Note carefully, whether the area has a floor below AC or non AC. Similarly, for the ceiling above. Ground floors could have basements, so floor below would be treated as non-AC.

Use a temperature difference of 5 deg f less than the outside DB temperature.

Sometimes, the floor below or ceiling above may be at different temperature, let's say a lower temperature, such as for Data Centres. Then, that needs to be accounted for. (and don't forget to insulate the slab to prevent sweating)! U Values ( 1/R ) Btu/hr/sqft

► 8” brick wall with ½” cement plaster both sides 0.35 ► 4” brick wall with ½” cement plaster both sides 0.44 ► 4” brick wall, with ½” and 1” expanded polystyrene 0.24 ► 6” RCC, with ½” plaster both sides 0.65 ► 4” RCC, ½” plaster both sides 0.71 ► 4” RCC, ½” plaster both sides, 2” polystyrene 0.12 ► ¼” or 6 mm glass 1.13 Gable Roof Transmission Gains – Walls and Roof Typical U values in Btu/hr/sq ft/Deg F

► 8” brick wall with ½” cement plaster both sides 0.35 ► 4” brick wall with ½” cement plaster both sides 0.44 ► 4” brick wall, with ½” and 1” expanded polystyrene 0.24 ► 6” RCC, with ½” plaster both sides 0.65 ► 6” RCC, with ½” plaster + 1 in Mosaic Tile 0.40 ► 4” RCC, ½” plaster both sides 0.71 ► 4” RCC, ½” plaster both sides, 2” thermocole 0.12 ► ¼” or 6 mm glass 1.13 Transmission Gain Thru Glass And Partition ► Add all the areas for solar glass, and then add any glass which is exposed to a non-airconditioned area. For transmission gain thru glass, use the difference between the outside and the inside design conditions. For transmission gains from partitions, use 5 degree less. Note, sometimes the partition, may be exposed to a hotter area like a kitchen or , in which case, please take care. Transmission Gains - Other Internal Heat Gains

equipment

people lights

appliances Lights

► The heat given off by lights both incandescent and fluorescent (and CFL), is not affected by the room temperature. It depends only on the electricity consumed. 1 Kw lighting load generates 3410 BTU/Hr. Ballast loads, copper ballast, electronic ballast. Halogen transformer issues. Watts per sqft. Office. Showrooms. Jewellery shops. Gain into return air plenum. Lights gain equation

►Lights:

►Area x watts/sqft x constant =Btu/hr

►A x (kW, W) x 3.41/3410 = q Return air plenum gain Appliances, kW or Watts

► Heat generated by computers. (Refer the booklet for other appliances). Usually, as per earlier IBM recommendations, this used to be 150 watts per PC, but would have now increased to 200 watts per PC. Remember, that for UPS's and Data Centers you need to be very careful in determining the heat generated. For UPS rooms, take 10% of the UPS rating, if it’s a digital UPS. For server rooms, there is no set norm, but usually, a 42 U rack would have equipment generating about 4 KW per server rack, right upto 10Kw per blade server rack. Electric Motors, H.P. ► The heat given off by electric motors, machines and appliances is also fairly independent of the room temperature. It depends on the actual electricity used. Nameplate ratings may not reflect actual loads.

Motors many times, are over loaded or under loaded. So a usage factor may be used to account for this.

In addition, the heat from the motor going into the room, depends on the location of the motor, whether within the room or outside the room.

1 H.P. = 2545 BTU/Hr. Equipment / Appliances gain equation ► (kW,W,HP) x Diversity Factor x constant = Btu/hr

► kW x D.F. x 3410 = Btu/Hr ► W x D.F. x 3.41 = Btu/Hr ► HP x D.F x 2545 = Btu/Hr People

►Heat generated by oxidation, called metabolic rate.

►Carried by:

►Radiation, convection (skin & breathing) ► of moisture from skin Heat Gain from People People gain equation

►People x Sensible gain/person = Btu/Hr Internal Heat Bypass factors Coils will have a small bypass and this will have to be factored into the heat load calculations The bypass at the coil, leaves some of the heat , directly entering the room and will add to the room heat If the bypass is 10% , 10% of the heat from the outside air will be added into the room directly , and 90% added to the coil load  The coil which has more rows , will have less bypass . As the moisture load on the coil increases ( as the fresh air load increases ) , we will require more rows in the coil design and this will lead to lower bypass factors  The velocity of air through the coil will also decide the bypass with lower velocities offering lower velocities Ventilation / Outside Air ( Fresh air ) Load outdoor air supply cooling or fresh air fan coil supply air

return exhaust air air air

space Bypass Factor

► Bypass factor calculation:

For 4 row coil = 0.1

6 row = (0.1) ^ 6/4 8 row = (0.1) ^ 8/4

(1-BF) is called Contact Factor. Bypassed outside air gain equation

►Outside air cfm x Temp.Diff. x Bypass factor x 1.08=Btu/Hr

►OA cfm x Temp.Diff x B.F. x 1.08 = Btu/Hr Infiltration

Infiltration is the leakage of untreated outdoor air through porous walls, floors, roofs, poorly sealed windows, etc. Infiltration can add a lot of moisture load into the conditioned space. Generally, infiltration is caused by wind velocity, or , or both. Infiltration Infiltration

►Air Change Method: ►(0.2 to 0.5 .)

►Effective Leakage Area Method. Added Load due to infiltration of Outside air

The air from outside could infiltrate into the conditioned space through the door cracks and this brings in both sensible and latent heat into the conditioned space

The amount of air that will leak in will depend on a. The crack width in the door frame b. The wind velocity outside CRACK IN Cfm leakage per linear foot length of door DOOR 5MPH 10MPH 15MPH 3/16 inch 4.8 10 14 1/8 inch 3 6 9 Infiltration gain equation

►Infiltration air cfm x Temp.Diff. x 1.08=Btu/Hr

►OA cfm x Temp.Diff x 1.08 = Btu/Hr Bypassed outside air and infiltration Safeties and Room Sensible Heat 2 Sources of Latent Loads

► Moisture entering the space from bypassed outside air and infiltration.

► Moisture through permeation from spaces at a higher vapour pressure.

► Moisture generated within the space from moisture generating objects. These objects usually include:

. occupants within the space . moisture generated by cooking or warming appliances . industrial or production machinery which evaporates water Latent Gains

►People ►Outside air ►Infiltration ►Equipment () Latent gains equation

► People x Latent gain/person = Btu/Hr

► Outside air cfm x Grains x Bypass factor x 0.68=Btu/Hr

► Infiltration air cfm x Grains x 0.68=Btu/Hr

► Steam lb/Hr x 1080 btu/lb = Btu/Hr Room Latent Heat and Room Total Heat Outside Air Heat and Safety Margins Sensible Heat Factor

►Effective SHF

Effective Sensible heat factor = ►Room sensible heat / Room Total heat

► ESHF = RSH / RTH ESHF ( Room sensible heat factor)

ESHF = Room sensible Heat Room Sensible + Room Latent heat

193075 Btu/hr 183075+9616 Btu/hr

ESHF =0.88 Apparatus Dew Point

►Depends on Inside Design Conditions

►Effective Sensible Heat Factor

►(Effective Sensible Heat Factor takes into account the effect of bypassed air). O SHF, ADP and Dehumidified cfm Dehumidified Air

►Temp. Rise = (1-BF) x (RoomDB – ADP)

►Dehumidified air =

►ESHF / (1.08 x Temp. Rise)

Note that the air quantity is inversely proportional to the temperature rise. Dehumidified Rise and CFM

The Dehumidified Rise = (Room Temperature – ADP)* (1-Bypass factor) (75-54 )*( 1-0.1)= 21*0.9= 18.5 F

Dehumidified CFM

The Dehumidified CFM = Room sensible heat Dehumidified rise *1.08

= 193075 = 9674 cfm 18.5*1.08 Est Zeeshan HEAT LOAD ESTIMATE Dtd 30-Apr-20 At 4pm Job HVACR Est SUMMER Peak Society Add. Karachi 24.9 Deg N Latitude

Space Office DB WB RH GR/LB Size 0.0 0.00 5120 SQFT 10.0 FT HT. 51200O.A. 99 74 21 88 Item Area Gain Factor Btu/Hr. Room 75 55 70 SOLAR GAIN - GLASS Diff 24 18 N glass 144 Sqftx 23 x 1.00 3312 VENTILATIO N E glass 192 Sqftx 12 x 1.00 2304 5120 Sq ft 0.06cfm/sft 307 S glass 144 Sqftx 12 x 1.00 1728 40 people 5cfm 200 W glass 192 Sqftx 163 x 0.56 17526 0 Doorsx 0cfm 0 SW glass 0 Sqftx 85 x 0.56 0 0 Crack 0 SE glass 0 Sqftx 12 x 0.56 0 0 Exhaust(excess) 0 NW glass 0 Sqftx 138 x 0.56 0 CFM VENTILATION 507 NE glass 0 Sqftx 12 x 0.56 0

HOR glass 0 Sqftx 0 x 0.00 0

GAIN-WALLS/ROOF

N Wall 576 Sqftx 13 x 0.35 2621

E Wall 768 Sqftx 27 x 0.35 7258

S Wall 576 Sqftx 25 x 0.35 5040

W Wall 768 Sqftx 21 x 0.35 5645

SW Wall 0Sqftx 31 x 0.35 0

SE Wall 0 Sqftx 26 x 0.35 0

NW Wall 0 Sqftx 17 x 0.35 0

NE Wall 0 Sqftx 19 x 0.35 0

R-sun 0 Sqftx 0 x 0.35 0

Roof Sun R-sh. 5120 Sqftx 44 x 0.12 27034 TRANS. GAIN S.H.F.AND ADP

All glass 672 Sqftx 24 x 1.13 18225 193075 RSH Partition 0 Sqftx 19 x 0.45 0 219723 RTH 0.88 SHF Ceiling 0 Sqftx 15 x 0.12 0 INDICATED . 53oF ADP Floor 5120 Sqftx 24 x 0.40 49152 SELECTED ADP 54oF INFIL.& DEHUMIDIFIED AIR OUTSIDE AIR

Inf. cfmx 24 oF x 1.08 0 0.88 21 = 18.5 O.A. 507 24 oFx 0.12 BFx 1.08 1578 193075 RSH INTERNAL 1.08 18.5 = 9674 CFM HEAT Occ. 40 People x 245 9800 Equipment Load 200Watts x 20 3.40 13600 Lights 0.30 Watts x 5120 3.4 5238 CHECK FIGURES

Appl. ( PC's) 2 230 3.40 1564 TR 18.31

Sub 171623 CFM 9674 total HEAT FAN SAFETY ADP DEG 54.0 F GAIN% 0.0 HP% 7.5 FACT 5.0 21453 CFMTON 528.3 ROOM SENSIBLE 193075 CFM/SFT 1.9 HEAT Inf. 0 cfmx 18 Gr/lb 1.00 x 0.68 0 400 CFM/TON 24.18 O.A. 507 cfmx 18 Gr/lbx 0.12 BFx 0.68 745 SQ FT /TR 279.6

Occ. 40 People 205 8200

Steam 0.00 lb/hr x 1080 0

Sub 8945 total LEAK 0 SAFET 0 0 Y LOSS% 0.0 FACT 7.5 671 % ROOM LATENT HEAT 9616

ROOM 202691 TOTAL HEAT S.H. 507 cfmx 24 oFx 0.88 x 1.08 11569 L.H. 507 cfmx 18 G/lb 0.88 x 0.68 5463 OUTSIDE AIR HEAT 17032 Grand Total Heat 219723 Sub-Total HEAT H.P. CHW GAIN 0.0 PUMP% 0.0 PPg% 0.0 0 % TONS 18.31 GRAND TOTAL HEAT 219723

PSYCHROMETRY INVOLVED

Mixed air

l Room Coi ass Byp RLH RSH Coil ADP Grand Total Heat

GRAND TOTAL HEAT IS

EFFECTIVE SENSIBLE HEAT 193075 Btu/hr + EFFECTIVE LATENT HEAT 9616 Btu/hr + OUTSIDE AIR HEAT 17032 Btu/hr +

GRAND TOTAL HEAT = 219723 Btu/hr

= 18.31 TR AIRCONDITIONING EQUIPMENT REQUIREMENT BASED ON HEAT LOAD

GRAND TOTAL HEAT = 18.31 TR

DEHUMIDIFIED CFM THROUGH COIL = 15989 CFM

The equipment selected should have 18.31 TR capacity and 9674 cfm air flow through the coil Check Figures

CHECK FIGURES

TONS 18.31 CFM 9674 ADP 54.0 CFM/TR 528.3 CFM /SQ FT 1.9 400 CFM/TON 24.18 SQ FT/TR 279.6 Munters Psychro App Load Calculation Check

►Did you consider window shading? ►Did you consider zoning? ►Did you consider infiltration? ►Did you consider insulating the roof? ►Did you consider toilet exhaust? References ► Carrier Handbook of Air conditioning System Design

https://www.scribd.com/doc/142002487/Carrier-Handbook-of-Air-Conditioning-System-Design-Part-1

►ASHRAE Fundamentals

► Consulting Engineer , Rajeev Kakkar

Thank you

Vikram Murthy ASHRAE Mumbai Chapter

[email protected]