A passive approach to keeping the interiors of apartment buildings and other structures cool has been advanced by University of Maryland and University of Wisconsin–Madison researchers. A microporous glass coating tamps down the temperature of the material it covers by 3.5° C at noon, even under high humidity conditions.

Finely ground glass particles serve as a binder in a radiative cooling material designed to withstand exposure to water, ultraviolet radiation, dirt and excessive heat. Aluminum oxide particles are incorporated into the glass coating, with particle sizes optimized to maximize emission of infrared heat while simultaneously reflecting sunlight.

The cooling glass described in the journal Science reflects up to 99% of solar radiation to prevent heat absorption by buildings. Heat is emitted in the form of longwave infrared radiation into the cold universe, where the temperature is generally around -270° C. In addition to reducing occupant energy use by preventing heat accumulation, use of the radiative cooling glass offers potential to reduce a mid-rise apartment building’s yearly carbon emissions by 10%.

[See also: Cooling ceramic promises to enhance energy efficiency for the construction sector]

Testing and development of the cooling glass, which can be applied to tile, brick and other surfaces, is ongoing, and the researchers launched a startup company — CeraCool — for its commercialization.