Glass buildings let in sunlight and heat. The problem is especially severe during Spain's hot, hot, hot summers. So aircraft engineers at the Universidad Politécnica de Madrid have found a way to use the windows themselves as cooling devices — cutting air-conditioning bills by 70%.

The method is a variation on double glazing: Two layers of glass are separated by a half-inch gap filled with circulating water that literally drains away the sun's heat. Confident that they've got a winner, the university researchers have created a spin-off company, Intelliglass, to market the technology to builders. — Al Boline

UPM Intelliglass (original Spanish, Google translation), via Habitat Futura and Treehugger