Cooling Glass Draws Cold Air from Space to Cool Buildings

A new type of glass coating can cool temperatures indoors without the use of electricity, instead drawing on cold from the depths of space as a way to help create more efficiency in climate-control solutions for buildings.

Researchers at the University of Maryland have developed the technology, a microporous glass coating that can lower the temperature of the material beneath it by 3.5 degrees Celsius at mid-day. This result can potentially reduce the yearly carbon emissions of a mid-rise apartment building by 10 percent, they said. 

“It’s a game-changing technology that simplifies how we keep buildings cool and energy-efficient,” said Assistant Research Scientist Xinpeng Zhao, one of the researchers on the project, which was led by Distinguished Professor Liangbing Hu from the university's Department of Materials Science and Engineering. “This could change the way we live and help us take better care of our home and our planet."

The coating works in two ways—one of which is quite literally out of this world—to cool buildings, the researchers said. One of the ways is by reflecting up to 99% of solar radiation to stop it from absorbing heat.

The second way is a bit more intriguing. The coating emits heat in the form of long-wave infrared radiation out into the icy universe. There the temperature generally hovers about -270 degrees Celsius, or just a few degrees above absolute zero.

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A phenomenon known as “radiative cooling" takes over from there, in which space effectively acts as a heat sink for the buildings, which dump large amounts of heat into the universe using what's called the atmospheric transparency window. This is a part of the electromagnetic spectrum that passes through the atmosphere without boosting its temperature and is the same concept that allows the earth to cool itself, particularly on clear nights, the researchers noted.

Material Stability and Durability

Scientists have already fabricated cooling coatings that can be used for glass and other materials to release heat. However, it has several key differences that lend to its general usability, the researchers said. It is environmentally stable, and it is able to withstand exposure to water, ultraviolet radiation, dirt, and even flames, with the capability to survive exposure of temperatures of up to 1,000 degrees Celsius.  

It's also versatile in that it can be applied to various surfaces, including tile, brick and metal—a range of construction materials beyond windows that also can be used to help cool buildings.

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To make the glass, the researchers used finely ground glass particles as a binder, which meant they could avoid using polymers and thus enhance its long-term durability outdoors, Zhao said. Further, the particle size used by the team was aimed at maximizing emission of infrared heat while simultaneously reflecting sunlight, he said.

Researchers published a paper on their work in the journal Science. To promote commercialization of the technology, they also have created a startup called CeraCool and plan to continue to develop and test the material for practical applications as a larger strategy to combat climate change.

“By cutting down on air conditioning use, we're taking big steps toward using less energy and reducing our carbon footprint," Hu said. "It shows how new technology can help us build a cooler, greener world."