Courtesy of Ivan Parkin and Troy Manning The coating viewed from above (top) and in cross section (bottom).

Glass Coatings for Selective Infrared Reflection

A glass coating technology that can selectively "know" when to reflect infrared rays based on ambient temperature was recently highlighted in Discover Magazine (Webb, 2004). This smart-glass technology can be designed to deflect the sun's warming infrared rays at times when cooling is needed, and to allow them to pass at other times when they are beneficial.

The glass coating relies upon vanadium dioxide molecules doped with tungsten to form a layer which selectively reflects infrared on hot days. At low temperatures, vanadium dioxide is transparent to infrared. Yet as the temperature rises, the bonding between the molecules changes and the material becomes reflective, like a metal. The amount of tungsten determines where this change occurs; a 2 percent mix makes it happen roughly at a comfortable room temperature. Parkin and Manning hope to overcome the coating's yellow-brown tone, which is unappealing to builders. They estimate that intelligent-glass windows could be on the market within five years, costing about 20 percent more than the ordinary kind. Given the ability to reduce heat gain through glazing, this technology could offer significant energy savings through reduced air-conditioning costs.

Reference:
Webb, Sarah. "Glass That Keeps Its Cool", Discover Magazine, November 2004.