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What's the right order for improving office lighting? Most retrofitters start by improving the lighting equipment. But that starts at the wrong end of the problem. Even the most efficient lighting equipment is useless if it lights the wrong place, or at the wrong time, or at the wrong angle so it causes glare. The Illuminating Engineering Society and seasoned lighting professionals would instead recommend the following sequence for, say, retrofitting the lighting in an ordinary office where people main read papers and computer screens:
Or consider the proper sequence in which to help people feel comfortable in hot weather:6
1 If you're having trouble reading because the papers have been photocopied on a machine with dust on the lenses and mirrors, clean out the machine first to make the image crisper. If there's glare off the paper, consider using matte paper. 2 If there's "discomfort glare" from harsh overhead sources, so shading your eyes with your hand like a baseball-cap brim makes your face muscles relax from squinting, control the glare with louvers or lighting redesign. If bright spots are glaring in your computer screen from lights or windows behind you, shade them or change the layout of the room so they're no longer behind you. If you can't read your computer screen because it's in front of a bright window, move the screen or shade the window. If windows are too bright compared to walls, adjust the blinds properly, or use microperforated blinds or diffusing curtains. 3 You need more light when you're older, or your eyes are more tired, or when you're doing finer or more critical tasks. Task lamps make it easy to get just the amount of light you want, where and when you want it. 4 Modern techniques such as double-curved lightshelves can do this quite evenly and without glare, even as much as 50+ feet in from the nearest window. Lightshafts and atria can bounce soft daylight many stories downward. Special methods, such as lightpipes and fiber optics, can even collect concentrated sunlight on the roof or outside the building, then deliver it as intense daylight far underground. In general, direct sunlight is too strong, producing glare that makes it harder to see, so instead of being "dumped" into the space, direct sunrays should generally be bounced back up onto the ceiling. Glass-topped partitions for private offices can preserve privacy, yet spread daylight better into adjacent rooms. 5 For example, how to operate Venetian blinds: they're supposed to be not closed like opaque curtains, but tilted so they throw daylight upward onto the ceiling. Then you can still see out, but the outside isn't unpleasantly bright. 6 Cler, G., Shepard, H., Gregerson, J., Houghton, D.J., Fryer, L., Elleson, J., Pattinson, B., Hawthorne, W., Webster, L., Stein, J., Davis, D. & Parsons, S. 1997: Commercial Space Cooling and Air Handling Technology Atlas, E SOURCE, Boulder CO, www.esource.com. 7 Herman Miller's "Aeron" chair lets you sit not on insulating upholstery but on a ventilative net or mesh, keeping your backside 47°F cooler. (In a nice example of design synergy, that "pellicle" also costs less than upholstery, so Herman Miller could afford to include extremely thorough and effective ergonomic adjustments to the chair without making it cost more.) Ceiling fans or other turbulent vertical air movementnot so strong that it would blow papers off your deskcan make you feel about 9°F cooler. "Superwindows" or other ways to block radiant heat from windows can greatly increase comfort. Efficient office equipment similarly radiates less heat at you than inefficient equipment. Appropriate dress codes can greatly increase comfort, and can also reduce the hard-to-accommodate differences in comfort requirements between men in suits and women in skirts and blouses. Just these kinds of measures can together save 2030% or more of the cooling energy, and can eliminate the need for air-conditioning in many climateseven quite humid ones. 8 This means designing the building with the right shape, orientation, shading, surface properties, mass, insulation, landscaping, and ventilation design, and then not releasing unwanted heat indoors through inefficient lights and equipment. Many of these improvements can be retrofitted: for example, dark roofs can be changed to lighter colors specifically designed to bounce solar heat away without looking uncomfortably bright to your eye. Shading devices or vegetation can be added where they were originally lacking. Careful control of external and internal heat gains typically lets a "ton" (3.52 thermal kilowatts) of cooling suffice not just for 250400 square feet of office space (a typical number in the U.S.), but for about 8001,000 square feet in a retrofitted building and 1,200 (more in milder climates) in state-of-the-art new offices. As we'll see, that severalfold reduction in required cooling power can save a lot of capital cost. 9 An experimental office retrofit for Pacific Gas and Electric Company designed a mainly indirect-evaporative cooling system with a whole-system design power of 0.14 kilowatts per ton25 units of cooling per unit of electricity. 10 This ingenious device, invented by Eng Lock Lee and concurrently by several U.S. heat-pipe companies for hot, humid climates, works like this. Precool the air coming into the building (you'll learn how in a moment). This will condense water out of the moist incoming air. Collect that condensate. Run it out of the building by gravity in a small pipe. Evaporate the water into the outgoing air, which, having already been dehumidified, is drier than the ambient air outside. This evaporatively cools the outgoing air nearly to the wetbulb ambient temperature. Capture that coolth with a heat exchanger and bring it back inside passively with a heat pipe. That's the source of cooling that you use to precool the incoming air. 11 This can be done either passively or with a very small and efficient fan, and can readily be added to most conventional ventilation systems. 12 Hydrocarbons, ammonia, or other relatively benign materials can be used with appropriate care, but halogenated refrigerants are a problem. Even once manufacturers complete the transition from outlawed ozone-destroying CFCs to interim HCFCs to chlorine-free HFCs, those HFCs will still be greenhouse gases thousands to tens of thousands of times more potent than CO2partly because once released, they can stay aloft for millennia.
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