About 10% of all the electricity produced in the world is used for air conditioning, and by some estimates that number is set to triple by 2050. So cutting down the cooling by even a tiny amount could have a huge impact on sustainability. That’s why a new microporous glass coating designed by Zongfu Yu, a professor of electrical and computer engineering at the University of Wisconsin-Madison, and colleagues Liangbing Hu and Xinpeng Zhao at the University of Maryland could make a big impact on energy use by keeping buildings cool in the first place.
Zongfu Yu
When painted on a building, the glass coating is able to reduce its interior temperature by more than 6 degrees Fahrenheit, limiting the carbon emissions of an average mid-rise apartment building by about 10%.
The team published details of its research Nov. 9, 2023, in the journal Science.
“This ‘cooling glass’ is more than a new material—it’s a key part of the solution to climate change,” Hu says. “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.”
Other researchers have developed similar reflective materials made of polymers, or rigid sheets of plastic. Yu says that these polymers, however, are prone to weathering or cracking and simply aren’t designed to last long term. The new coating, made from particles of aluminum oxide and glass, is able to withstand exposure to water, ultraviolet radiation, dirt, fire and temperatures up to 1,000 degrees Celsius. It can also be applied to surfaces like tile, brick and metal. That’s why this glass material is a big step forward in creating a more practical reflective coating.
So how does it work? First, the material is able to reflect about 99% of the solar radiation that reaches it, keeping buildings from getting hot in the first place. Its second advantage is its ability to create “radiative cooling.” Most heat released by the earth and other objects, like buildings and roadways, radiates as infrared energy, especially at night. Much of that energy is released in wavelengths that are absorbed by Earth’s atmosphere. But certain wavelengths pass through what’s called the atmospheric transparency window, radiating directly into outer space, which is a very fast and effective way to cool down. This new coating emits heat as longwave infrared radiation in this window, meaning that it’s very good at shedding excess heat; in fact, Yu says it’s possible for it to radiate so much heat that a building could fall below the ambient temperature at night.
Developing the material took more than just crushing up glass and aluminum oxide. In this case, particle size really matters. That’s why Yu used an optical simulation software based on the finite difference time domain method (FDTD), developed by his spinoff company Flexcompute, to model the coating and optimize the particle size to ensure its reflective and radiative properties. “Modeling this kind of random media is extremely computationally expensive,” he says. “This project was enabled by the use of massive computing power.”
That high-tech computing, he says, has led to what he believes is a robust product that is close to commercialization. “I think it’s already pretty viable, and the team continues to lower the cost of manufacture because it does not involve a cleanroom or large panels that can be expensive to transport, unlike previous methods,” he says. “All you have to do is make a solution, then paint these nanoparticles on a wall. So this approach fundamentally removes some of the challenges associated with previous, expensive processes.”
In fact, Hu and Zhao have founded a spinoff company called CeraCool that is testing new commercial iterations of the coating.
Other authors include Tangyuan Li, Hua Xie, Lingzhe Wang, Yurui Qu, Stephanie Li, Shufeng Liu, Alexandra Brozena and Jelena Srebric of the University of Maryland.
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