Without curtains, blinds, or other window covers, rooms can heat up quickly when the afternoon sun streams through a window. Close the curtain or pull down the blind, and the room may cool down, but you lose views of the garden or backyard. Even window film can still offer some transparency, but it often includes tinting that can disrupt the view. Scientists have been working to solve this dilemma, and they may have just made it happen with a newly developed clear window coating.

A team of researchers from University of Notre Dame and Kyung Hee University in Seoul, South Korea have developed a window coating that fully blocks heat, even from the afternoon sun. 

“The angle between the sunshine and your window is always changing,” Tengfei Luo, lead author of the study and the Dorini Family Professor for Energy Studies at the University of Notre Dame, said in a statement. “Our coating maintains functionality and efficiency whatever the sun’s position in the sky.”

The researchers explained that while heat-blocking window coatings and coverings are not a new concept, coatings tested in recent studies tend to let ultraviolet and infrared light through when the sun is positioned at certain angles.

Two team members, Luo and Seongmin Kim, postdoctoral associate at the University of Notre Dame, previously developed a window coating made from silica, alumina and titanium oxide with an additional micrometer-thick silicon polymer to better reflect thermal radiation and block heat from coming through the windows.

The team then needed to optimize the order of the layers of the coating to block heat from all angles throughout the day. They used quantum computing to make this happen, finally settling on an optimized window coating that stayed transparent but reduced the temperature in a room by 5.4 to 7.2 degrees Celsius. The researchers published these findings in the journal Cell Reports Physical Science.

“Like polarized sunglasses, our coating lessens the intensity of incoming light, but, unlike sunglasses, our coating remains clear and effective even when you tilt it at different angles,” Luo explained.

The resulting window coating could be used not just for homes and residential buildings but also on vehicles to reduce heat gain and reliance on air conditioning. According to the study, cities throughout the U.S. could reduce energy use for cooling by up to 97.5 megaJoules (MJ) per square meter, and the coating could help cities reach up to 50.5% of cooling energy savings when applied to conventional windows.

This could be particularly important in reducing emissions, as the International Energy Agency reported that air conditioning usage currently accounts for about 10% of total global electricity consumption, and the agency estimated that global energy demand from air conditioning could triple by 2050. 

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