Effective daylighting solutions
December 7, 2010
Diagram courtesy of Viracon, Owatonna, Minn. Elements such as light shelves, sunshades and set-back windows improve efficiency, particularly when high VLT glass is specified above light shelves for maximum light transmission, and more moderate VLT glass below to prevent glare and heat gain.
Don McCann, architectural design manager for Viracon Inc., Owatonna, Minn., calls it a checkerboard. Mike Krasula, senior commercial marketing manager at NSG Pilkington, Toledo, Ohio, calls it a patchwork. "A patchwork of blinds—some blinds open, some blinds closed. That's what I see when I look at the buildings in downtown Toledo," he says.
A consequence of ineffectual daylighting, this "patchwork" effect is the result of building occupants pulling their shades to protect against glare, and is an example of how poor daylighting design can create inefficient structures and uncomfortable environments.
"It's convenient to say that daylighting is simple—just letting the light into a space," says Stephen Selkowitz, head of the building technologies department, Lawrence Berkeley National Laboratory, Berkeley, Calif. "But because it involves a number of factors, daylight strategies for sustainable design are still not commonly implemented in a fully satisfactory way, and still do not constitute standard practice in most buildings."
According to Selkowitz, effective daylighting requires a three-tiered strategy:
- Elements to admit adequate daylight (e.g. glass area, properties, location)
- Elements to control excessive daylight transmittance (e.g. glare and sun control as a function of weather, time, season)
- Elements to manage electric lighting energy use based on the presence of useful daylight (e.g. sensors, dimming ballasts)