Lawrence Berkeley National Laboratory Recent Work
Title EFFICIENT DAYLIGHTING IN THERMALLY CONTROLLED ENVIRONMENTS
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Authors Ne'eman, E. Selkowitz, S.
Publication Date 1981-10-01
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LAWRENCE ENERGY & ENVIRONMENT BERKELEYLABORATORV DIVISION NOV 1 3 1981
LIBRARY AND DOCUMENTS SECTION To be presented at the International Passive and Hybrid Cooling Conference, Miami Beach, FL, November 11-13, 1981
EFFICIENT DAYLIGHTING IN THERMALLY CONTROLLED ENVI.RONMENTS
E1iyahu Ne~eman and Stephen Selkowitz
October 1981 TWO-WEEK LOAN COPY
A." ··~
Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48 DISCLAIMER
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Plenary paper to be presented at the International Passive and Hybrid Cooling Conference, Miami Beach FL, November 11-13, 1981
EFFICIENT DAYLIGHTING IN THERMALLY CONTROLLED ENVIRONMENTS
Eliyahu Ne'eman * Stephen Selkowitz
Energy Efficient Buildings Program Lawrence Berkeley Laboratory University of California Berkeley, California 94720
OCTOBER 1981
*Permanent address, Faculty of Architecture and Town Planning at Techn- ion, Israel Institute of Technology, Haifa, Israel.
This work was supported by the Assistant Secretary for Conservation and Renewable Energy, Office of Buildings and Community Systems, Buildings Division of the u.s. Department of Energy under Contract No. W-7405- ENG-48. 1
EFFICIENT DAYLIGHTING IN THERMALLY CONTROLLED ENVIRONMENTS
Eliyahu Ne'eman* Stephen Selkowitz Energy Efficient Buildings Program Lawrence Berkeley Laboratory University of California Berkeley, California 94720
*Permanent address: Faculty of Architecture and Town Planning at Techrtion, Israel Institute of Technology, Haifa, Israel.
ABSTRACT of ultraviolet radiation.
This paper reviews many of the design con Historically, daylight has been the primary siderations required to enable a design team source for indoor illumination. However, the to utilize daylight to the maximum possible development of efficient electric sources, extent in order to reduce electric lighting particularly the fluorescent lamp, enabled loads and associated building energy-consump designers to rely increasingly on man-made, tion. Among steps that must be taken is a controlled environments. As part of this thorough analysis of all heating and cooling approach, electric lighting and mechanical loads inside the building and the heat cooling have been used as substitutes for exchange through the building envelope. Data daylight and natural ventilation. on local climate and sunshine availability This freedom from dependence on natural must also be considered. energy sources has greatly benefited Although the energy aspects have recently designers. However, excessive reliance on dominated our design considerations, mechanical technologies has caused designers daylight's influence on·human well-being is to lose their feeling for the mutual rela gaining importance. In this respect, the tionship between the building and its sur variability of daylight, the quality of its rounding. As a result, on the one hand win spectral composition, the view out, and dowless buildings were built and on the health effects are among the aspects that other, fully glazed buildings were con should be considered when determining an structed. Designers were seldom bothered by appropriate role ·for daylighting in energy any adverse environmental consequences of efficient buildings. their designs. They easily prescribed energy-consuming remedies in the form of additional lighting and air conditioning. 1. INTRODUCTION This approach can no longer be applied. Daylight, the visible part of solar radia Since energy has become expensive and scarce, tion, is regarded as the preferred light source for· interior lighting. However, day we have to relearn how to live in a world where energy must be conserved. light cannot be considered separately from the entire spectrum of radiation received It should be emphasized that solar heat, from the sun. On the thermal side, one must which is associated with daylight, is gen consider the total thermal balance to arrive erally desirable indoors during the heating at the optimal energy-conserving solution. season, while it is undesirable during the On the visual side, one ·must avoid glare cooling season. However, the glare associ from direct sunlight, the sky, and external ated with daylight should be prevented all bright surfaces. Furthermore, one cannot year round. The best way to avoid undesir ignore the physiological and health aspects able thermal and visual consequences is to 2
carefully design the size of openings, giving lat-ing dayUght for non-uniform sky condi due consideration to their orientation,and to tions becomes complicated. The International provide for controllable shading devices. Commission on Illumination (C.I.E.) adopted t~~ standard sky luminance distributions: 2. DAYLIGHT AS A SOURCE FOR INTERIOR "The Standard Overcast Sky " (see C. I.E., LIGHTING 19701) and the "Standard Clear Sky'' (see C.I.E., 19732). Data on the integrated irra As concern for efficient energy use in build diance and spectral distribution of solar ings has increased, designers have improved radiation can be found in C.I.E. (1972).3 For their understanding of thermal processes in the partly cloudy sky, Kireev (1979)4 indi buildings and the thermal environmental fac cated that when the sun disc is fully covered tors that drive those processes. The average with cloud, skylight levels approximately designer's level of knowledge concerning follow the overcast sky pattern. When the illumination and the luminous environment is sun disc is fully clear, the clear-sky dis less well develo'ped; thus we include a short tribution can be applied. review of daylight sources and the luminous properties associated with each. Daylight Several methods for calculating daylight can can usually reach a building's interior in be found in the following books and papers: three ways--direct sunlight, skylight, and Hopkinson, Petherbridge and Longmore (1966);5 light reflected from external surfaces. Lynes(1968); 6 and Krochmann and Aydinli (1979); 7 Bryan et al (1981);8 Modest (1981);9 2.1 Sunlight and Ne'eman and Shrifteilig (1979).10
Direct sunlight is associated with several 2.3 · Overcast Sky undesirable effects, such as glare, fading, and excessive heat gain during hot per'iods. For the C.I.E. Standard Overcast Sky, the Thus, it is rarely regarded as a source for luminance distribution is described by an direct interior illumination, although if equation proposed by Moon and Spencer properly diffused and reflected, it can be (1942): 11 effectively utilized. A variety of sun 1 + 2cose: control options is available to prevent the L L (2) e: 0 3 penetration of unwanted sunlight.
~ is the luminance of a small area, p, of 2. 2 Skylight the sky (see Fig. 1) at an angle £ from the
The primary source of daylight inside the zenith. L0 is the sky luminance at the zen built environment is usually the sky. The ith. Thus the luminance of any point on the sky's illuminance, E, on a small surface can sky depends only on the angle of that point be calculated by the following equation: from the zenith (or horizon).
E = f L·dS"l (1) z where L is the luminance of the source (sky) and Q the solid angle subtended by this source on the examined ~urface.
For an unobstructed horizontal surface out N doors, the solid angle of the whole sky vault is 2n, and for a uniformly bright sky (L constant), the illuminance can easily be cal Fig. 1. Coordinates for the calculation of culated. However, the luminance distribution daylight from the clear and overcast sky. of the real sky is never uniform, and calcu- 3
The illuminance, Ea, on the horizontal sur 2.4 Clear sky face, s, from a small area, p, of the sky will }'(;: Daylight under clear-sky conditions is the sum of direct sunlight and skylight, with the addition of externally reflected light. The E = /L(£) 'cos£ 'drl (3) a P latter component is particularly significant and if we substitute dn by: drl sine: • de: • whenever sunlight is reflected from bright surfaces. Daylight levels with clear sky d8 no' we can write: depend on the height of the sun above the 1 + 2cos£ Ea L • •Cose:·sine:·d£ ·d8·rl (4) horizon, which is determined by the day in 0 3 0 If the year, the hour, and also the clarity of the atmosphere expressed as turbidity factor Qo a unit solid.angle • 1 Steradian, and 6 is 2 the azimuth angle. (see C.I.E. 1973 ). The intensity of direct solar radiation, Ees• can be expressed (Kro Integration of (4) for a horizontal surface chmann, Aydinli, 19797 by: with the unobstructed sky vault 2 (j3 21T and e: = 2!.) gives: E (y ,T)(w/m ) = E •exp(-~ ·m·T)siny (7) 2 es s eo R s 7 E L n (5) (on a horizontal surface) a grr 0 0 where E eo is the solar constant. According Although the distribution of luminances for to recent measurements, it is specified as the overcast sky is independent of the posi Eeo • 1370 w/m2 or 128.41 klx. Also, aR tion of the sun, the values of luminance are the mean extinction coefficient, is a func- determined by the height of the sun above the tion of the optical air mass, m. T is the 12 horizon, Ys. Krochmann (1963) suggested turbidity factor according to Linke. that the horizontal illuminance from the whole overcast sky should be calculated by The calculation of daylight with clear sky is the following equation (see Fig. 1): far more complicated than with overcast sky. The pattern of luminance distribution moves Ea Other equations were proposed by Krochmann When we examine the luminous efficiency of (1970), 14 Kittler (1972) , 15 and Dogniaux electric light sources, we define it as the (1976). 16 ( quotient of the total luminous flux emitted by the total power consumed. The luminance distribution of clear sky was defined by Kittler (1965) 17 and adopted as a In order to examine the energy-conserving standard distribution by the C.I.E. in 1973: potential of daylight, luminous efficiencies of daylight as well as of electric light 0 32 30 2 L (l-e- • sec£) (0.91+10e- +0.45cos o). L. sources are given in Table 1: P -3z o 0.2738S(0.91+10e 0 +0.45cos2z ) (9) 0 UILE 1 .fte LaaiDOu. Effictea.ct C~/v) of Uaht Soarc:ea LP = luminance of the sky element p. L • luminance of the zenith. - efficf.eacy (111/v) 0 5 1 £ • angle of the sky element from the zenith -·· 11D1>Uuo1t (1966) . Ldklt (1978) 8 o • angle of the sky element from the sun. ::fi:~~ (aolu altitude 7 .so) ,., (oolllr altituda > %5°) 117 • Z0 angle of the sun from the zenith. (_.. , 100 109.2 • 10.4 1t7Uabt (anrqa) 125 114. 9.3 2.5 Luminous Efficiency (clau) uo Global (aftraaa) 115 110 • 5.1 By evaluating the "Luminous Efficiency," LE, lleccrJ.c liabt aourcn* (la/v) of radiation (lm/w) we can calculate the IDI:aadeaeea.t 10- 15 Pluoreacea.t 60-70 intensity of sunlight from solar radiation ~lite• or ·c~e-lu:e· floureaceDt 40- 50 ... ~icolour· floureacent 65-75 measurements. The luminous efficiency of 11Jb-effic1eDCy fluoreac.ent 75- 90 witt. alectrcnUc ballaat direct sunlight is the quotient of luminous 11ah-J'Ireaaure aercurr 50-60 llatal baUdo 70- 90 flux from the sun by the corresponding solar liah-praaaura IIOdtua 100 - 120 radiant flux, and is expressed by 780nm ....a dlroa.ah Ufe; b&llaet lo••••• where appUcable, are iacludecl. / LE K 380nm Ees,A· V(A) ·dA (10) m For further comparison between daylight and electric light sources a few examples of ~ • 673 lm/w • maximum luminous efficiency spectral distribution curves are given in (555 nm). Ees A is the intensity of solar Fig. 2. radiation in wav~length A.V(A)is the spectral relative sensitivity of the average human 2.6 Daylight Factor eye, according to C.I.E. Values for the luminous efficiency of solar radiation are Because of daylight's ·variable nature, it is given in Table 1. useless to specify it in absolute values. Daylight is commonly specified by the "Day The total illuminance from the whole clear lighting Factor," which is defined as the sky can be calculated .by using diffuse radia- quotient of indoor illuminance at the exam tion measurements and multiplying them by the ined point to the illuminance outdoors, meas appropriate luminous efficiency values. In ured on a horizontal surface with unob- this case we replace Ees, A in equation (10) structed sky. Sunlight excluded from both by Ees sky, ~)--which is the intensity of measurements. diffuse radiation. E In real conditions we are usually exposed to DF • ~ x 100 (%). (11) out the global illuminance, and again we can cal culate it from global radiation measurements with the aid of luminous efficiency for the global· radiation. 5 statistical average duration of real sunshine as a percentage of the possible duration with a clear and unobstructed sky. ·Naturally, exact data on availability of sunshine are available for only a few areas. 50 1000 Lumen However, detailed analysis of sunshine avai 1,0 Incandescent Larr.p lability in Great Brittan, carried out by "' Another difference between the overcast and excessive exposure to UV radiation, notes the clear sky should be mentioned. The overcast beneficial effects of moderate exposure. In sky is in many cases brighter than the clear the Soviet Union, it is customary to expose blue sky, which implies that the intensity of miners and children in far Polar regions to daylight indoors is also higher under over controlled doses of UV radiation (Dantzig, cast conditions. However, we must add the 1967).28 effect of the externally reflected component, which is much higher with the clear sky than People who spend all their time indoors, and with the overcast sky. do not have even an occasional exposure to v sunlight, may become "photo-deprived·· and may 4. DAYLIGHT FOR WELL-BEING not sufficiently develop their immunologic defenses (Logan, 1972).25 Among the benefits Daylight has been and still is the reference of admitting sunlight indoors we mention the light source to which the ·human eye is germicidal and bacteriocidal effects. We adapted. No man-made, "artificial" source also note the anti-fungus effect and the dry can fully match its spectral composition. We ing, anti-rot effect. wish to stress the importance of daylight and the associated contact with the outside world 4.2 Psychological Effects to occupants' well-being. Sunlight and daylight are not just sources of 4.1 Physiological Effects light. They are associated psychologically with the inflow of visual information about We can happily note that since the widespread the outside world, and thus help combat a utilization of electric lighting began at the sense of enclosure. Marcus (1967),29. Ne'eman end of the last century, no negative effects and Hopkinson (1970),30 Hardy (1974),31 and on human health have been found. Further Ne'eman (1974)32 dealt with the various more, the introduction of efficient and low aspects of daylight and windows and their luminance flourescent lamps after the Second role in creating psychological well-being. World War enabled us to improve the indoor visual environment by increasing lighting The importance occupants attach to daylight levels and. uniformity of distribution and by and view seems to depend on individual sub reducing glare. Still, we cannot be fully jective considerations such as interest in assured that negative effects do· not exist. the work, type of activity, primary direction The flourescent and other discharge sources of view in relation to the window, availabil used for indoor illumination are not continu ity of sunshine outdoors, etc. ous in their spectrum and are deficient in ultraviolet radiation. Also, indoors we are Up to now, there has been no general agree exposed to only 1/100 to 1/200 of the light ment on the strength of occupants' desire for intensities prevailing in sunny conditions daylight and view. However, the authors outdoors. Warnings have been made that the believe that both daylight and view are distorted sensory information caused by non essential for occupants' well-being. Conse continuous light frequency patterns can be quently, whenever a conflict between day harmful to people performing prolonged visual lighting and energy conservation arises, activities. Logan (1972)25 writes, "We can- measures to conserve energy should be taken without sacrificing the minimum acceptable . not yet be sure what the artificial indoor level of daylight and view. electromagnetic environment is doing to man, but all should be aware of the possibili- 4.3 Adverse Effects of Daylight ties." Skylight is rarely a cause of undesirable Deprivation of UV irradiation may be poten effects indoors. One of the few cir tial health hazard (Thorington, 1971). 26Dutt cumstances occurs in museums and art gal- (1978), 27 while examining the damage from 7 leries where conservation of the art objects dictates tight control of light intensities, particularly UV radiation. High levels of daylight may also accelerate the fading of sensitive fabrics and other organic materi als. In addition to increasing cooling loads and creating thermal discomfort, direct sun ------_""!...0...!~~~-=------light can cause glare which may be of much annoyance where occupant position and direc tion of view are fixed. School classrooms, Fig. 3. Daylight penetration and artificial offices, and industrial buildings are a few light supplement. examples. examine the savings potential of daylight, we However, these negative effects can be elim need to estimate the energy consumption of inated by using appropriate sun-control the artificial lighting. With overall effi strategies. ciency of approximately 50%, the power con 5 • ENERGY BALANCE sumption of a domestic incandescent general lighting installation providing levels of 150 Well-being is one side of daylighting, while to 250 lux will be about 20 w/m2 to 33 w/m2. the energy balance and the consequent cost is For visual activities requiring illuminance the other. Daylight is not free of cost. We levels of 500 to 1000 lux, and utilizing do not pay for its generation, but fenestra flourescent lamps, the load can be 18 w/m2 to tion and the associated· window management 35 w/m2 • An average load of 25 w/m2 can gen devices are often more expensive than the erally be assumed. For all daytime hours in equivalent opaque wall. Thus, initial the year, the _consumption will be 112 kwh/m2, investment for a daylit structure may be and about half that amount for an office, on higher than for a windowless building. the basis of 10 hours per day operation for Furthermore, it is well known that windows 200 days a year. can increase the demand for energy. Because of the many factors involved, including local Many investigations have been carried out in climate and building systems, it is impossi recent years to establish the potential sav ble to analyze here the full energy balance ing in electric energy by using daylight. 33 of buildingo, However, we shall discuss the Matsuura (1979) has calculated the distance main aspects of daylight which influence the from the windows for which daylight is ade energy balance. quate, so that artificial lighting can be switched off, Hunt (1979),34 in his paper on 6. DAYLIGHT/ ARTIFICIAL LIGHT BALANCE lighting controls, compared "on-off" switch ing with "top-up" dimmers that provide only The penetration of daylight depends mainly on enough light to top-up the level to its the area of the windows and their transmit- specified value. He has shown that for an tance. However, even with fully glazed illuminance level of 500 lux, and an interior external wall, daylight is not effective in having a glazed area that provides 2% Day 'ti' deep interiors, those farther away than 3 to light Factor, the yearly gross saving may 5 times the ceiling height. A characteristic reach about 60%. Crisp (1978)35 investigated daylight penetration is given in Fig. 3. efficient facilities for light-switching in In deep interiors daylight cannot substitute buildings. Initial results from field tests for all electric lighting, even on bright of dimmable electronic ballasts for floures days. On cloudy-dull days, daylight levels cent lamps indicate that savings of 50-75% are lower, so the electric lighting may need are achievable in typical perimeter offices. to be used throughout the day. Before we can Although sophisticated lighting control sys- 8 tems may appear economically prohibitive at died the effect of orientation on thermal and present prices, there is little doubt that lighting conditions in classrooms. Givoni 41 they will rapidly become feasible due to the (1976) also dealt with the subject. rising prices of energy. Data on solar radiation and solar gain can be 6.1 Deep Interiors obtained from various guides and also from Petherbridge (1974), 42 ASHRAE Handbook of ·The optimal solution for deep interiors is to Fundamentals (1977),43 and Pilkington utilize daylight as far as possible and sup Environmental Advisory Service (1979).44 plement with electric lighting in the deeper These data allow one to evaluate heat- part. The concept was originally developed transfer values for any building type and any by Hopkinson (Hopkinson and Longmore, window/shading combination. 1959),36 and is known as P.S.A.L.I.- Permanent Supplem~ntary Artificial Lighting The "Shading Coefficient" (SC) is used to of Interiors. P.S.A.L.I. is not just an compare the solar radiant heat gain of dif extension of night-time electric lighting to ferent glazing systems. It is defined as the daytime. The design approach is based on the ratio of heat gain from the glazing system to dominance of daylight, while electric light the heat gain from a single sheet of 1/8" DS is used only as a supplement. For other con clear glass. For simple glazing systems, SC cepts of integrating daylight and electric can be calculated. For more complex fenes light, see Hardy and O'Sullivan (1967 )37 and tration systems it is usually measured in a Ne'eman and Longmore (1973).38 solar calorimeter. · 6. 2 Lighting Savings Potential 7.1 Glazing Summing up, the maximum feasible saving on Good-quality clear float glass, 3-4 mm (1/8" artificial lighting can be up to SO%· of the 3/16") thick, has 0.90 visible transmit gross yearly use in larger rooms •.In offices tance. However, "heat-resistant," "anti the saving can be 25-35 kwh/m2 of floor area sun," or "anti-glare" tinted glasses have a per year. In school classrooms, conventions~ light transmittance of 0.25 to 0.55, and some offices, and similar buildings where the dis~ reflective glasses have a transmittance as tance of the far wall from windows does not low as 0.08. By·installing such glasses we exceed 2 to 3 times the ceiling height, sav permanently reduce the amount of light admit ings can be even greater. ted. Inevitably this reduces opportunities to substitute daylight for electric light. Some 7. DAYLIGHT/THERMAL BALANCE of these glasses reduce light transmittance even more than the total radiant heat The thermal optimization of a building transmittance. For example, Pilkington 6 mm requires examining internal sources and heat (3/8") 41/60 grey float glass has 0.41 light transfer through both the opaque and the transmittance, 0.60 total radiant heat transparent parts of the outer envelope. transmittance, and a shading coefficient of Although they affect the overall energy bal 0.60. On the other hand, blue-green glass ance, lighting considerations have only a selectively absorbs more infrared energy so minor influence on the thermal behavior of that it has 0.50 light transmittance and 0.35 the opaque portions of the envelope. Conse total radiant heat transmittance. quently, we can concentrate on windows alone. In many cases where permanent reduction of The intensity of solar radiation on a hor light transmittance is not desirable, izontal surface is given in Equation (7) daylighting design would recommend clear above. Further details on solar radiation glass. The proper shading coefficient can be can be obtained from Robinson's book obtained by suitable shading devices. How- (1966). 39 Givoni and colleagues (1968)40 stu- 9 ever, specific solutions will vary with cli c. The intermediate zone, where both winter mate, orientation, and other design con heating and summer cooling are required straints. for thermal comfort. Regions having a temperate climate belong to this group. In cold regions, heat losses during the cold season can be reduced by double glazing and In cold regions, during the heating season, suitable shading. The thermal transmittance the heat generated by the electric lighting (U-value) for single glazing is about 5.5 and solar radiation is helpful because it w/m2 oc. For double glazing the U-value is reduces the load on the heating ·plant. about 3.2 w/m2 °C, while for double-glazed Therefore, large glazing areas, with little windows and external sun controls it is only attention to effective shading, can be 2.9 w/m2 °C. Even lower U-values can be acceptable.!£ heat and light can be intro obtained from low-emittance coatings, triple duced into the building without sacrificing glazing, or movable insulation. thermal or visual comfort. Thermal insula tion is obtained by double or triple glazing 8. ENERGY MANAGEMENT DURING COOLING SEASON to which movable insulating devices may be added. We often assume that commercial buildi~gs are dominated by cooling concerns. This is true The situation differs in warm regions during for very large buildings having large inter the cooling season. Any addition of heat nal heat sources, but is not necessarily true into the cooled space, either from electric of small commercial buildings, which make up lighting or from solar radiation, increases the bulk of the building stock. Nor is it the load on the cooling plant. In addition, true of buildings having efficient designs electric lighting increases the building's that minimize internal loads. peak electrical load and the total demand on summer-peaking utilities. Although cooling We can examine design concerns based upon the strategies can utilize storage that shifts following climatic zones: cooling load from the on-peak hours, lighting and daylight utilization are instantaneous a. The cold zone, where heating is the pri phenomena which must be properly managed mary thermal-design consideration, while throughout the day. In the intermediate zone cooling is almost unnecessary if the a combination of fixed and operable thermal design is based on natural ventilation. and daylighting control strategies may pro Northern parts of the United States, vide the optimal solution. Canada, northern Europe, and Asia, and equivalent regions in the southern hemi The appropriate design strategy for buildings sphere belong to this group. characterized primarily by their cooling requirements should include: b. The warm zone, where the predominant requirement is cooling. In this zone, a. Minimal utilization of electric light interior thermal comfort during the hot during the daytime peak cooling period. season cannot be provided by natural b. Maximum utilization of natural light ventilation, either becaus'e of high during the daytime. The primary sources ambient temperatures, high relative for natural light should be skylight and humidity, or both. Southern parts o{ externally reflected light (from sun and the United States, equatorial countries sky). of South America, Africa, and southern Europe, the Middle East, and southern c. The penetration of direct solar radia Asia belong to this group. tion should generally be prevented by effective shading, preferably with external controllable devices. Such devices should allow maximum utilization 10 of available daylight when the openings have accelerated the development of sophisti are not exposed to direct sunlight. cated design tools.S These computational tools can allow accurate predictions of day d. Automatic switching or, even more effi light levels at any point in the building and cient, automatic continuous dimming of can be used by designers who do not have groups of lamps based upon available expertise with or accessibility to large com .., daylight; can increase the energy sav- puters. ings compared to manually operated con trols. Powerful computational tools may be used to generate other design methods for use e. Ultimately, a fully automatic system, , throughout the design process. Methods based which would regulate both the electric upon tabular data, nomograph&, protractors, lighting and the shading controls, could and graphic overlays have been devel?ped for provide the optimal ene~gy and load designing daylit interiors. reductions while preserving the well- In many situations involving interaction of direct sunlight with geometrically complex being of occupants. While systems of shading systems it is difficult or impossible this type are becoming commercially to calculate interior daylight levels. In available, little documentation yet these circumstances, scale models may prove exists on operating experience. The helpful. Since the interreflectance of a combined systems approach is important light flux in a geometrical volume is scale because inadequate control of solar gain independent, measurements made in scaled may increase cooling loads and reduce models of proposed buildings can be used to the energy saved by lowering electric lighting levels. predict quantitative daylight levels in the 9. DESIGN METHODS full-scale building. Scale models can also be used to assess lighting quality, view, glare, Daylighting was for generations an art based and the aesthetics of the. daylit spaces. on intuition and experience. Methods for If scale-model measurements are made out predicting daylight illumination in buildings doors, the changing sky luminance conditions have been developed only during the last few decades. However, the theory and calculation must be carefully documented, or comparisons tools that were adequate to determine compli between different model measurements diffi ance with building codes based upon minimum cult or impossible. One is also dependent on (e.g., overcast) sky conditions could not the vagaries of local weather and may experi cope with the increasing complexity of the ence long waits until conditions recur. One subject, particularly for clear sky. solution to these problems is to build an indoor sky simulator that provides a stable Only in the last 20 years has an improved understanding of sky and sun characteristics sky of constant and known luminance distribu enabled researchers to formulate internation-· tion. Such sky simulators range from the ally agreed upon equations for the sky lumi very simple (an illuminated sheet adjacent to nance distribution of the overcast sky1 and a scale model) to the large and complex (dome the clear sky.i However, accurate calculation skies that allow designers or researchers to of daylight could not be easily performed work within them). A newly completed, 24- without computers. Several large computer foot-diameter hemispherical sky at Lawrence programs that calculate daylight illumination Berkeley Laboratory will permit modeling stu are currently available (DiLaura and Hauser, dies under overcast, uniform, and clear sky 1978).45 SUPERLITE, a program under develop conditions and will duplicate sunlit ground ment, will allow calculation of the effects conditions (Selkowitz et al, 1981).46 A sun of complex shading systems exposed to direct simulator is currently being added to the 9 sunlight. facility, which will be used for research, teaching, and design. Programmable calculators and small computers 11 The design methods discussed above provide 8. Bryan, H.; Clear, R.; Rosen, J.; and Selkowitz, s. 1981. Quicklite 1: a data on interior daylight illumination and daylighting program for the TI-59 cal may be used to predict hour-by-hour values culator. lD&A June: 28-36. throughout the year. However, in order to 9. Modest, M. 1981. Daylighting calcula predict the consequences for energy use, tions for non-rectangular interior including thermal tradeoffs, daylighting spaces with shading devices. 'Ib be tools must be merged with an annual building published in Journal of the Illuminat ina Erx:Jineering Society. energy analysis program. Simplified day lighting models have been incorporated into 10. Ne'eman, E. and Shrifteilig, D. 1979. The design of openings for given day several building energy analysis programs, light requ:irenents as function of a but these are generally limited to modeling topolcgical structure and geometry of simple fenestration systems. A flexible and light admission. In Proceedings of the 19th CIE Session, Kyoto. Paris: CIE. powerful set of algorithms that will model light shelves and complex shading is now 11. Moon, P. and Spencer, D.E. 1942. Illu being added to DOE-2. mination from a non unifonn sky. Illu rninatin::J Engineering 37: 707. 12. Krochmann, J. 1963. tiber die Horizon talbeleuchtungsstarke der 'Iagesbeleuch 10. ACKNOWLEDGEMENT tung. Lichttechnik 15 (11). This work was supported by the Assistant 13. Chroscicki, w. 1971. Calculation meth Secretary for Conservation and Renewable ods of detennining the value of day Energy, Office of Building and Community Sys light intensity on the ground of pho tems, Buildings ·Division of u.s. Department tcmetrical and actinanetrical rneasure rrents of unobstructed planes. In Proceed of Energy under Contract No. W-7405-ENG-48. ings of the CIE Session, Barcelona. Pa 11. REFEREN:ES ris: CIE. 1. CIE. 1970. Daylight, international re 14. I 2. CIE. 1973. Standardization of luminance 15. Kittler, R. 1972. Standardization of the distribution on clear skies. Publica solar radiation with regard to the pre tion No. 22 (1C-4.2). Paris: CIE. diction of insolation and shading of . buildings. Paper presented at Teaching 3. CIE. 1972. Reoammendations for the in the Teachers Conference, Stockholm. tegrated irradiance and the spectral distribution of simulated solar radia 16. Dogniaux, R. and Laroine, M. 1976. Pro tion for testing uurposes. Publication grarnne de calcul des eclairanents s~ No. 20 (TC-2.2). Paris: CIE. aires energetigues et lumineux de sur faces orientees et inclinees. Misc. Se 4. Kireev, N.N. 1979. Rating of daylight ries C, No. 14. Ins. 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A hemispherical and Technology 6(3):159-164. sky simulator for daylightirx; studies: design, construction and operation. 33. Matsuura, K. 1979. 'I\.lrning-off line in 'Ib be published in Journal of the Illu perimeter areas for savirs lightir¥;l en- minating Engineering Society. This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable. t <10 ,;~, :.1 ~ .. ~ TECHNICAL INFORMATION DEPARTMENT LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 ..