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The prize will be to discover a switchable tinted window that responds to light and heat gain by absorbing rays while allowing light to penetrate. The only problem is that any such technology must clear a number of hurdles before making it to the marketplace. There are many companies in competition to develop an electrochromic or chemical window solution that can darken and lighten windows at the flick of a switch or by automatic sensor. "Much of this development is heavily cloaked in secrecy as patents are sought and technology continues to develop," explains Head.
Building a Better Window
| |  | | | Electrochromic windows switch from light to dark with the flip of a switch. Several companies including Sage Electrochromics, manufacturer of the window seen above, are working on designs reliable enough for residential and commercial use.
Credit: Sage Electrochromic | | | The key stumbling blocks are threefold: durability, thermal stability, and reliability with regard to switching. Gentex Corporation, a Zeeland, Michigan company, known for its electrochromic automobile mirrors that automatically darken and lighten to eliminate glare, is undergoing its own tests for electrochromic windows. "We've made increases in durability, fairly significant ones," says Tom Guar, Vice President of Chemical Research for Gentex. Still, the goal has to be to produce a window that can stand up for 20 years. "When you think about it, it's a pretty tough environment," Guar says of the stresses a window designed to absorb heat must endure. "If you think about your glass pane absorbing great amounts of light and heat, it will get very hot, maybe even crack the glass," he says. Add to that susceptibility to water penetration, which is a problem for all insulated glass units (IGUs), and oxygen penetration, and there's a lot to overcome. Marvin struggled with making sure the film adhered to the glass and the seal remained undisturbed. Any future product will need to address the same issues.
Faribault, Minnesota's Sage Electrochromics, makers of SageGlass, has developed an electrochromic window technology that has passed all four levels of testing by the Department of Energy. To get DOE approval, Sage must demonstrate that their product is durable as well as efficient. "There are three key reasons why this approval is so critical," says Mike Myser of Sage. "The first is durability. In order for a window company to sell our product they need to know it's durable, and will withstand the thermal stress and UV degradation of the sun." Sage is the first to receive DOE approval for durability. With this approval in hand, Sage can partner with glass and window manufacturers to create a product that will be available to consumers for home use.
Making Window Efficiency Affordable
"I think their technology is very good," admits Guar. Still, as he sees it, the key will be to produce a window that is affordable, reliable, and durable. The manufacturing implications are huge, he says. "Handling large sheets of glass is non-trivial," Guar says. Covering that glass with a chemical film is even harder. "It's not an easy thing to accomplish," Guar says. Still, the right partnership would make the glass available to window companies who feel they could provide a dependable seal for this technology. The fact that Sage is partnering with Honeywell to provide the switching capability gives a great boost to their product.
Granted, there are technologies available that use advanced chemical solutions to address energy efficiency. Heat Mirror is an excellent product that was developed to insulate glass from heat loss and heat gain. Heat Mirror windows have an insulative reflective barrier that is suspended between the panes of glass. It is spectrally selective and allows visible light to enter while blocking near infrared rays that cause heat buildup. It functions like a third layer of insulation and greatly increases the R-value of walls with windows. But, while the R-value with Heat Mirror windows is exceptional, the cost for insulating windows of this caliber is very high. And they're not switchable. The key to winning the high efficiency window race, most experts agree, is to produce an affordable technology that can be mass produced and last for the lifetime of a standard window warranty.
Changing the Way We Work With Windows
SageGlass plans to offer an affordable technology that is durable, reliable, and ripe for the market. "We're trying to change an industry," explains Myser. Consumers want more glass, but they demand efficiency and control. Bringing electrochromic device technology to the window industry will allow homeowners to control the amount of light and heat that enters the building. "People want skylights, they want windows in their homes, the light it brings, but what do they do about the heat? We've solved that. Switchable control means controlling both the light and the heat," Myser says. Since the SageGlass coating is applied to only one of the panes of glass, their hope is that they can provide affordable switchable technology to the window industry and its customers.
"People understand this technology and want to buy it," Myser says. For homeowners it could revolutionize window placement and home design. It would mean windows where you want them, not just where heat gain can be reasonably avoided. This technology may even allow designers to place windows on west-facing facades without sustaining the incredible burden a beating western sun places on the air conditioning system. It may also mean designing for the glorious morning sun that so many homes currently avoid. Better yet, since this technology is device-controlled, it can even be programmed to darken or lighten automatically so that indoor climates can be effectively controlled even when the homeowner is absent.
The EnergyWise House in an ongoing project that examines energy efficient building techniques, materials, and methods. For more information on the materials and companies participating in the project, see the EnergyWise House Video Resource Library.
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© 2001 BobVila.com
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