THE POSITIVE EFFECTS
It's another beautiful day at the office. Golden morning sunshine streams in through enormous crystal-clear windows. You perform a strange hand-waving dance as you try to chase an obscuring yellowish haze from your computer screen. Beads of sweat form on your brow; only the plants on your desk thrive in the greenhouse-like conditions. Before too long the air conditioning kicks in, even though it's only 60 degrees outside. Regretfully, you drop the blinds, switch on the electric lights, and get to work--leaving the beautiful day for others to enjoy.
It's an all too common scenario that plagues indoor environments: daylighting gone bad. But the intentions are good. Research has shown that people who live and work in daylit environments are likely to be more productive, healthier, and happier. What's more, the sunlight is free, so you can cut costs by saving money on electric lighting. At least in theory.
In practice the result can be soaring costs, blocked windows, and frustrated humans groping in the dark for solutions.
"Most current daylighting has passive solar gain with no glare control," explains Energy Center program manager Abby Vogen. "It gets hot and the cooling bills go through the roof, taking away whatever savings you're getting from using natural light--so you're not saving money and not doing much good for people."
Vogen manages the Center's new initiative called the Daylighting Collaborative. Its mission is to make successful daylighting part of mainstream construction. Vogen says daylighting is successful when it is "cool."
"Simply having lots of windows isn't effective daylighting. Cool daylighting is designed to decrease solar gain over that of conventional construction."
Wherever sunlight enters a building, the interior heats up. And building designers are well aware of the consequences: they use the amount of planned window area to determine how big the cooling system needs to be. A typical commercial building spends the vast majority of its energy resources combating solar gain and, ironically, providing artificial light.
"Solutions to lighting and unwanted solar gain are the cornerstones of building efficiency," says Steve Ternoey, an architect who specializes in daylighting and is the technical director for the Collaborative. "These are far and away the most important places to save energy." He says that cool daylighting, when properly designed, can cut 30 to 70 percent from typical lifetime energy and lighting costs. This is in addition to the construction savings you get from being able to install a smaller cooling system.
The choice isn't "clear"
Some daylighting designs use complex equipment like light-sensing dimmers and automatic electronic window coverings to manage glare and solar gain. But--and this is at the heart of the Collaborative's philosophy--there are much easier, much cheaper, and far more effective ways to do it. And anyone can do it successfully in any building.
"Right now the field is too specialized and high-tech, so it's expensive and overly complicated," Vogen says. "The simpler techniques usually work better anyway."
Perhaps the most important simple element in cool daylighting design is "low-transmittance" window glass, which transmits only a small portion of the sun's light and heat.
Ternoey says glass technology has come a long way from unpopular "tinted" windows; today's low-transmittance glass is color-neutral, so once people's eyes adjust to indoor light levels they hardly notice it.
"Clear glass is definitely wrong," Ternoey says.
But getting away from clear glass isn't enough. To eliminate the most intense solar gain, Ternoey also uses exterior overhangs specifically designed to block the high summer sun.
"You only have to shade glass on the hottest days of the year. Then your cooling energy use plummets and you've found a way to pay for your daylighting system."
What does a daylighting system cost? In addition to glass and shading, successful daylighting requires an integrated design that considers window placement, interior design (such as reflective colors and interior windows to spread the daylight), levels of artificial lighting, and even the shape of the building. But cool daylighting design, although different, is no more complicated--and typically no more expensive--than traditional designs.
Cool daylighting uses low-transmittance glass, exterior shading, and partial window blinds to ensure that daylighting is cool, glare-free, and always available. Perimeter electric lights work like streetlights, operable only at night.
"You don't need high-priced design consultants or expensive high-tech equipment to take advantage of daylighting," Vogen says. And although low-transmittance glass does cost more than clear glass, using it cuts the size of the cooling system, making up for most, if not all of the extra construction cost. Anything left over is quickly covered by the long-term energy savings that cool daylighting promises.
Written by: Jeremy Kohler, Energy Center of Wisconsin
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