Daylight Illumination of Building Interiors (Daylighting) Ross McCluney, Ph.D. Principal Research Scientist Florida Solar Energy Center A research institute of the University of Central Florida 1679 Clearlake Rd., Cocoa, FL 32922 www.fsec.ucf.edu 1 Outline # Benefits of Daylighting # Daylighting and Energy # Assessing System Performance # Potential Problems # Quality lighting — Spectral — Spatial — Psychological # Design options # Ancient Traditions 2
Daylighting Benefits 3 Daylight Illumination P Cool, natural daylight has good color rendering P Daylight is healthy, has psychological benefits P Daylighting can displace electric lighting, saving energy P Reduce air pollution, global warming, and dependence on foreign sources of energy 4
Goals of daylighting design P Provide good quality daytime interior: < illumination < view P Provide good visual comfort for occupants < Happy people are productive people < Productive people improve output P Avoid common problems < Glare < Overheating P Displace daytime electric lighting and save electrical energy costs P Occupancy is critical 5 Daylighting and Energy 6
Daylighting and Electric Lighting Comparison To deliver 1000 Lumens per square meter 133.3 W/m 2 of illuminated area Incandescent light requires 26.67 W/m 2 Flourescent light requires 2.78 W/m 2 Daylight requires Ratios of energy cost, electric lighting to daylighting: Incandescent lighting 133.3÷2.78 = 48 to 1 Fluorescent lighting 26.67÷2.78 = 9.6 to 1 Savings not around the clock all year long. But an energy efficient window does not cost much energy. Daylighting is generally the single greatest energy saving strategy one can have in an otherwise energy efficient office building. 7 How daylighting saves energy Electric lighting system Luminous efficacy K s / Lumens of light Unit: Lm/W Watts of electricity Daylight radiation luminous efficacy K r = 100 to 160 Lm/W In comparison: Fluorescent lighting system K s = 40-60 Lm/W Incandescent lighting K s = 8-12 Lm/W In the middle of a bright day, let’s provide 1000 Lm/m 2 of illumination. (This is about 100 ft-candles) 8
Providing 1000 Lux of Illumination To provide 1000 Lumens per square meter, and remove the heat produced by the lighting with an air conditioner C.O.P. of 3 using: P Incandescent light requires P 1000 Lm ÷ 10 Lm/W = 100 watts of electricity per sq. m. P Plus 100 ÷ 3 = 33.3 W for heat removal P Total: 133.3 W/m 2 P Flourescent light requires P 1000 ÷ 50 = 20 watts of electricity per sq. m. P Plus 20 ÷ 3 = 6.67 W for heat removal P Total: 26.67 W/m 2 P Daylight produces a heat gain of P 1000 ÷ 120 = 8.33 watts P and 8.33 ÷ 3 = 2.78 watts for heat removal P Total: 2.78 W/m 2 9 Summary: To deliver 1000 Lumens per square meter 133.3 W/m 2 Incandescent light requires 26.67 W/m 2 Flourescent light requires 2.78 W/m 2 Daylight requires Ratios of energy cost, electric lighting to daylighting: Incandescent lighting 133.3÷2.78 = 48 to 1 Fluorescent lighting 26.67÷2.78 = 9.6 to 1 These savings with daylighting do not take place around the clock all year long. An energy efficient window does not cost much energy. Daylighting is generally the single greatest energy saving strategy one can have in a relatively energy efficient office building. 10
Assessing System Performance 11 Solar Lighting System (SLS) Performances Illumination Energy Thermal Displace Quality Quantity energy electric impacts lighting Color Light rendering level Direct Conduction Solar heat energy gain transfers savings Glare Coverage avoidance area Net energy Cost of impact energy User satisfaction Annual dollar savings & productivity ($) 12
Potential Problems P Glare P Overheating, draftiness P Noise P Physical impacts P Privacy 13 Glare Primer P Disability glare P Discomfort glare 14
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P Disability Glare P Light reflects off of the target or otherwise masks or reduces contrast of the target, disabling the visual task. P Example: Window reflected from computer screen P Discomfort Glare P Light, usually from the side, is brighter than that of the visual task, enters the eye and causes visual discomfort. P Example: Bright window to the side, much brighter than the computer screen or the book you’re trying to read, or the person seated opposite you. You can see the true visual target, but not clearly. After a while you get a headache. Removal of glare source induces comfort. 17 Glare Sources ! The sun ! Reflected beam sunlight ! Bright window surrounded by dark walls and furnishings ! Bare electric lamps, incandescent and fluorescent ! Poorly designed electric luminaires ! Improperly used luminaires 18
Dealing with Glare from Windows P Direct beam sunlight P Path of the sun through the sky P Avoiding beam radiation P Managing beam radiation P Even diffuse sky light can be a problem 19 SUMMER WINTER Sun rises south of due east, Sun rises north of due east, sets south of due west, sets north of due west, and is low in the sky at and is high in the sky at noon noon Shade: southwest to west to Shade: protect west window on overhang for noon warm winter days east to northeast morning west to northwest afternoon 20
Direct Beam Solar Radiation Can produce discomforting glare and localized overheating, as well as add to the air conditioning bill. 21 Avoiding Direct Beam 22
Orientation & Shading Strategies N Minimize East and West Exposures Wide overhangs Fence Closet Garage Buffer East and West Exposures Utility room 23 Block solar gain before it reaches the window 24
Sunpath on Summer Solstice at a southern latitude 25 Summer Sun — Morning and Afternoon East-facing West-facing 26
Glare from diffuse daylight P Bright window with dark surround produces glare P Window brightness the same regardless of size P Room brightness a combination of total daylight admitted and electric illumination P Small windows, dark walls, and inadequate electric lighting results in poor luminance balance – glare P Large windows, bright walls, minimal electric lighting provides better quality and good energy savings 27 Quality Lighting P Spectral P Spatial P Psychological 28
Solar Spectrum 1.6 1.4 Solar spectrum 1.2 1.0 Human eye sensitivity (Visible portion of the 0.8 spectrum) 0.6 0.4 0.2 NIR UV VIS 0.0 0 500 1000 1500 2000 2500 Wavelength in nm Near Infrared (NIR) Ultraviolet (UV) 29 Color 8 8 Reflected light whose Source Apparent Illuminant with its color is defined by the color object color own characteristic color of the incident color beam and the spectral reflectance (inherent color) of the object Object with spectral reflectance R( 8 ) 72 30
CIE 1931 Chromaticity Coordinates 0.9 520 530 0.8 Locus of 510 540 monochromatic colors 0.7 550 Green 560 0.6 500 570 0.5 580 y 590 0.4 600 White 620 490 0.3 Red 830 0.2 480 0.1 Blue 470 360 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 x 31 Source Color Rendering CIE 1931 chromaticity coordinates 0.9 520 530 0.8 510 540 0.7 550 Green 560 0.6 500 570 0.5 Locus of blackbody 2,856 580 y colors 590 3,500K 0.4 600 White A D65 2,000K 620 490 1,500K 0.3 4,500K Red 830 500K 6,500K 0.2 10,000K Blue 480 470100,000K 0.1 360 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 x 32
High Quality Spatially P Glare free P Adequate quantity P Shadows for good depth and shape perception 33 High Quality Psychologically P In our evolutionary past, information on time of day, seasonal changes in vegeta- tion, in weather, and in other forms of environmental ‘data' had a pronounced influence on survival and health. P Thus, it made sense to pay attention to changes in daylight that provided < time cues < assessment of cloud formations for information about future weather conditions P These events influenced our ancestors' daily decisions, such as where to sleep at night, as well as much more difficult decisions such as where to look for food next week. P It is not surprising, therefore, that loss of natural information on time of day has been implicated in the poor recovery of patients in windowless intensive care units. P “Once you start thinking about it, [daylighting] design makes perfect sense." "We didn't evolve in a sea of gray cubicles." — Judith Heerwagen, principal of J. H. Heerwagen and Associates and senior scientist at the Pacific Northwest National Laboratory in Seattle. 34
Humans need connections with the outdoors, with Nature P It’s built into our genetic makeup P It promotes health and a sense of well-being P It makes us happier and more productive P (as if worker productivity were the most important measure of a building’s performance) P Even photographs of Nature on the wall have been proven helpful P If we cannot live outdoors, at least let’s introduce some of the outdoors to the indoors 35 Design Options 36
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