Lawrence Berkeley National Laboratory Recent Work Title EFFICIENT DAYLIGHTING IN THERMALLY CONTROLLED ENVIRONMENTS Permalink https://escholarship.org/uc/item/5vd9w20r Authors Ne'eman, E. Selkowitz, S. Publication Date 1981-10-01 eScholarship.org Powered by the California Digital Library University of California LBL-13399 ITll Lawrence Berkeley Laboratory li:l UNIVERSITY OF CALIFORNIA 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 This document was prepared as an account of work sponsored by the United States Government. 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LBL-13399 EEB-W-81-23 W-107 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.