Using advanced computing methods and artificial intelligence, researchers have designed a clear window coating that lowers the temperature inside buildings. The coating could reduce the energy used to cool indoor spaces by 31 percent compared with normal glass windows in hot climates.
The material, reported in the journal ACS Energy Letters, lets visible light through, but blocks the sun’s warming infrared and ultraviolet rays. It also radiates heat from the window at a wavelength that passes through the atmosphere into outer space.
Cooling homes and buildings consumes 15 percent of the energy that the world produces. And the planet’s warming climate is pushing people to use more energy-intensive air-conditioning. The number of air-conditioners around the world is expected to go up from 1.6 billion today to 5.6 billion by 2050, doubling carbon emissions from powering these units.
To reduce this burden, researchers have been on the hunt for low-energy alternatives to cooling indoor spaces. Windows are a big part of a building’s cooling energy waste because they let in warmth from the sun. So one promising route to passive cooling is to coat windows with materials that block infrared light, but such films can also block visible light so they appear dark or frosted. Another option for electricity-free cooling are materials that radiate heat into space.
Researchers from Kyung Hee University in South Korea and the University of Notre Dame wanted to make a smart window coating that combines the best of these features. They turned to computer modeling to design a material that is transparent, but also radiates heat into space.
The material consists of alternating super-thin layers of common materials like silicon dioxide, silicon nitride, aluminum oxide or titanium dioxide on a glass sheet, topped with a plastic film. Using machine learning and advanced quantum computing, they created many iterations of the design with different types, orders and combinations of layers. Then they made a film using the best design that the models came up with.
Then they tested the cooling performance of the new material by putting it on top of a chamber placed outside in Phoenix, AZ for 37 hours. At the end, the chamber was 6°C cooler than a similar chamber covered with conventional glass.
To estimate how well the coating would work as potential window material, the team calculated the energy it can save per year for a standard office with two windows in 16 U.S. cities. On average, each square meter of the new coating saved 50 Meagajoules of energy annually. In hot climates like Phoenix, it saved 31 percent of cooling energy consumption.
Further, the team did the same calculations for several major cities worldwide. The results show that “all locations will benefit from the proposed [coating] as window materials to save cooling energy, and such a saving can be very significant in tropical regions,” they write in the paper.
The film can be manufactured using state-of-the-art material deposition techniques, so they could be made on large scale for practical applications, they add.
Source: Kim, S., et al. High-Performance Transparent Radiative Cooler Designed by Quantum Computing. ACS Energy Letters, 2022.
Image Credit: ACS Energy Letters