Ordinary windows are dumb: They let in the sun’s warming infrared rays whether it is sweltering or freezing outside. So Ivan Parkin and Troy Manning at University College London have developed “intelligent glass,” which selectively reflects the infrared on hot days. Skyscrapers that incorporate this smart material could save millions of dollars a year in air-conditioning costs, the researchers estimate, while cars with smart-glass windows could remain relatively cool even in blinding sun.
The secret is a superthin coating of vanadium dioxide molecules doped with tungsten, Parkin says. At low temperatures, vanadium dioxide is transparent to infrared. At higher temperatures, the bonding between the molecules changes and the material becomes reflective, like a metal. A dose of tungsten determines where the switch occurs; a 2 percent mix makes it happen roughly at a comfortable room temperature. Parkin and Manning are talking to commercial glassmakers about applying the coating process to industrial-scale manufacturing. Another hurdle is the coating’s yellow-brown tone, unappealing to builders because it looks dirty; adding other ingredients could neutralize the color. Within five years, Parkin estimates, intelligent-glass windows could be on the market, costing perhaps 20 percent more than the ordinary kind.