Buildings and Cities
A one-time luxury, glass windows are now standard across the world, bringing light and visibility into the built environment without inviting in the weather. Except windows do let in the weather, in the form of heat or cold. They are much less efficient than insulated walls at keeping room temperature in and outside temperature out—by a factor of ten or more.
Various measures can improve a window’s efficiency: layered panes, reflective low-emissivity coatings, insulating gas between panes, and tightly sealed frames. More adaptive technologies, dubbed “smart glass,” make windows responsive in real time to sunlight and weather, reducing a building’s energy load for lighting and improving heating and cooling efficiency.
Smart glass relies on chromism, the term for any process that causes material to change color. Electricity triggers it in electrochromic glass: When exposed to a brief burst of voltage, ions move into another layer of glass and the tint and reflectiveness change. Thermochromic glass is triggered by heat: Based on outside temperature, it transitions automatically from transparent to opaque and back again. Photochromic windows operate similarly, on the basis of light exposure. Currently challenged by cost, smart glass will become much more common in the coming decades.
Technical summaries for each solution will be available May 1, 2017.