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“Cooling Glass” Tackles Heat Without Air Conditioning

The corner of a mid-rise apartment building, as seen from the ground. There is a shaded balcony and many visible windowpanes.
Credit: Étienne Beauregard-Riverin / Unsplash.
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Researchers at the University of Maryland have developed a new microporous glass coating that can cool indoor temperatures without using electricity. The new technology could lower a mid-rise apartment building’s annual carbon emissions by up to 10%.

The new glass coating reflects incoming solar radiation while also emitting heat radiation out into the cold universe, a phenomenon called “radiative cooling”.

While radiative cooling materials are not new, many other radiative cooling strategies require the use of polymers to work. This new “cooling glass” is an interesting alternative to these other materials, the researchers say, as its harder nature should make it more robust to long-term weathering. It is described in the journal Science.

Novel materials to cut down on carbon emissions

Temperature control technologies such as air conditioning are a significant contributor to worldwide greenhouse gas emissions. According to recent calculations done by scientists at the National Renewable Energy Laboratory, air conditioning is responsible for releasing the equivalent of 1,950 million tons of carbon dioxide annually, or just under 4% of all global greenhouse gas emissions.

Finding new, more energy-efficient alternatives to traditional air conditioning systems could stand to make a significant dent in global emissions.

In their new paper, the researchers present a microporous glass coating for buildings that reflects up to 99% of incoming solar radiation to prevent buildings from absorbing heat and becoming too warm in the first place. The new coating also uses the radiative cooling phenomenon to emit heat and actively cool down the environment behind it.

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Passive radiative cooling materials, such as this new cooling glass design, take advantage of the so-called “atmospheric transparency window” – a part of the electromagnetic spectrum that passes through the atmosphere without increasing its temperature – to effectively dump heat into the icy universe, where temperatures are only a few degrees above absolute zero. This same phenomenon is what the Earth uses to cool itself on clear nights, although to a much less intense degree than engineered radiative cooling materials.

“It’s a game-changing technology that simplifies how we keep buildings cool and energy-efficient,” said assistant research scientist Xinpeng Zhao, the first author of the study. “This could change the way we live and help us take better care of our home and our planet."

A tougher approach to radiative cooling

The new cooling glass is a composite of a microporous glass framework and aluminum oxide particles, which together work to emit heat radiation and scatter incoming sunlight.

The researchers’ choice to use finely-ground glass particles as a binder was a deliberate decision, as this allowed them to avoid using polymers and thus enhance the outdoor durability of the coating. Similarly, the team carefully selected the particle size of this glass to maximize the emission of infrared heat while simultaneously reflecting sunlight.

According to the new research paper, the resultant microporous glass coating can lower the temperature of materials beneath it by up to 3.5 °C at noon. Additional calculations show that the use of this material in a standard mid-rise apartment building could potentially reduce that building’s annual carbon emissions by 10%.

"This ‘cooling glass' is more than a new material – it's a key part of the solution to climate change,” said Liangbing Hu, distinguished university professor and director of the University of Maryland’s Center for Materials Innovation. “By cutting down on air conditioning use, we're taking big steps toward using less energy and reducing our carbon footprint. It shows how new technology can help us build a cooler, greener world."

Reference: Zhao X, Li T, Xie H, et al. A solution-processed radiative cooling glass. Science. 2023;382(6671):684-691. doi: 10.1126/science.adi2224

This article is a rework of a press release issued by the University of Maryland. Material has been edited for length and content.