December 7, 2010
Photo by Guardian Industries Corp., Auburn Hills, Mich. Waterplace in Salem, Ore., features several daylighting control strategies, including exterior light shelves and some frit on the glass. The insulating glass units feature Auburn Hills, Mich.-based Guardian Industries’ CrystalGray substrate for the outboard lite with Guardian SunGuard SuperNeutral 54 solar-control coating, and a clear inboard lite. The combination of the daylighting control devices and the solar control glass products allows for the benefits of natural light while mitigating the issues of glare and heat gain.
In response to architect demand for glass with higher visible light transmission, the glass industry has introduced products touting previously unimaginable VLT numbers. "We're seeing double silver coatings with VT of up to 70 percent, and triple silver coatings with VT up to 62 percent," says Don McCann, architectural design manager, Viracon Inc., Owatonna, Minn.
This demand for higher VLT rose along with the push for better U values and solar heat gain coefficients, resulting in the creation of low-emissivity coatings, and then spectrally selective low-E coatings. Traditional low-E products reflect longwave radiation from the sun, reducing heat loss. Spectrally selective low-E products go one step further, maximizing light transmittance and reducing transmission of longer wavelengths, in effect reducing heat loss and heat gain.
"We've created a range of glass transparency options in neutral colors that can more effectively reflect solar heat than any products in the past," says Chris Dolan, director of commercial glass markets, Guardian Industries, Auburn Hills, Mich. "Coated glass products are available, with a low-E coating applied to the No. 2 surface, that offer visible light transmission in the 40 to 68 percent range–for a neutral glass look combined with solar heat gain coefficient as low as .23, with lots of options in between. This means the glass is highly efficient in transmitting light but still blocks 77 percent of direct and indirect solar heat."
Glass companies have made continuous improvements to their products to allow even more visible light while blocking even more heat. "Of course, architects also need to consider proper VT versus simply just high VT, considering the appropriate balance of VT, solar heat gain, and glare control," Culp adds.
Glazing frame suppliers have also gotten on board, developing products like sunshade systems that block heat before it enters a building and light shelves that allow light to penetrate farther into a structure.
"There has always been a demand for more VLT, but this demand has historically been impeded by technology," says Jot Chahal, product manager, curtain walls, sun control and BIPV, Kawneer North America, Norcross, Ga.
"However, achieving a high VLT without compromising the energy performance of the buildings is becoming easier with continued advancement in materials, products, systems and energy-management strategies. These advancements will continue to support increased VLT in the future."
Looking at the future of daylighting design, McCann expects to see even higher performing coatings and use of tinted substrates. "We're ... looking at alternatives that haven't been looked at before," he says. "We're getting close to maxing out on some things with coatings, and I think we'll see some breakthroughs with different metals."
Mike Krasula, senior commercial marketing manager at NSG Pilkington, Toledo, Ohio, expects to see more dynamic products, switchable glass products and photovoltaics.