Green Windows

Two new technologies for making windows more energy efficient.

First, electrochromic glass:

Electrochromic glass, with changeable opacity, is one new avenue of exploration. Some of the most promising is produced by a firm called Sage Electrochromics, based in Minnesota. Its product, which consists of sheets of glass with a metal-oxide coating, was first used in skylights in 2003. When a voltage is applied across the coating, the window darkens, allowing less light to enter but still permitting a view. America’s Department of Energy (which developed low-e coatings in the 1970s) has used this glass, along with an insulated sash, to develop a “zero-energy” window that saves more energy in reduced heating and lighting than it needs to operate.

John Van Dine, Sage’s founder, says his company is about to invest in a new production facility that should reduce costs enough to make electrochromic windows competitive for homes by 2010. The company is also working on continuously variable darkening (current models have only two settings) and windows that are powered entirely by self-contained solar cells.

It would be cool to be able to get rid of the drapes and replace them with glass that can block out the sun.

Second, vacuum-insulated panes:

An even bigger leap may come from refining an older idea. Sheets of glass separated by a vacuum could bring windows’ insulating properties up to par with insulated walls, yet allow them to be nearly as thin as single panes of glass. The idea of vacuum-insulated panes has been around for nearly a century, and NSG/Pilkington, a Japanese firm that is one of the biggest glassmakers in the world, has sold such panes since 1996. But they remain a technical challenge: the difference in temperature causes the inner and outer sheets of glass to expand by different amounts, so that NSG/Pilkington’s windows can be used only where the temperature difference is less than 35ºC, which rules out many homes in need of insulation.

David Stark thinks he has a solution. His company, EverSealed Windows, based in Colorado, has patented a metal baffle bonded to both sheets of glass that allows them to expand and contract separately, while maintaining a vacuum that he says will last for decades. Mr Stark says vacuum-insulated windows at competitive prices could be on the market in three years. This could precipitate a big shift in the window industry, and its focus on spacers, adhesives and sealants: “All of that goes out the window,” he says.

According to their website, 12% of all energy in the US is lost out of windows. If they could create a window that insulates as well as a wall at a competitive price, that would be a huge energy savings.

via The Economist