MIT researchers develop window coating to deflect most of sun's heat

Nov. 9 (UPI) -- Scientists have developed a heat-deflecting film that could reject up to 70 percent of the sun's heat from a window.

Researchers published the results of tests with the film in a study published Thursday in the journal Joule.

The film resembles transparent plastic wrap, implanted with tiny microparticles that contain water that releases when met with temperatures higher than 85 degrees Fahrenheit. After squeezing out the water, the microparticles contract into tight clusters of fiber that repel light.

"It's like a fishnet in water," Nicholas Fang, a professor of mechanical engineering at MIT, said in a press release. "Each of those fibers making the net, by themselves, reflects a certain amount of light. But because there's a lot of water embedded in the fishnet, each fiber is harder to see. But once you squeeze the water out, the fibers become visible."

About a year ago, Fang began research with scientists at the University of Hong Kong who were eager to develop technology to ward off heat from the inside of buildings during the city's well-known hot summers.

The technology has its financial benefits as well. Air conditioning cost roughly $29 billion to use annually, accounting for 6 percent of all electricity use in the United States. To cut those costs and the inefficiency that come along with heavy air conditioning use, the researchers set out to create technology to protect office buildings from the nasty summer heat in Hong Kong and the U.S.

"Meeting this challenge is critical for a metropolitan area like Hong Kong, where they are under a strict deadline for energy savings," Fang said, in reference to Hong Kong's aim to reduce energy use by 40 percent by the year 2025.

The researchers produced the heat-shielding microparticles solutions, then placed it between two 12-by-12-inch sheets of glass. After applying light from a solar simulator onto the window, they discovered the film pushed back 70 percent of the heat it emitted

"Smart windows on the market currently are either not very efficient in rejecting heat from the sun, or, like some electrochromic windows, they may need more power to drive them, so you would be paying to basically turn windows opaque," Fang said. "We thought there might be room for new optical materials and coatings, to provide better smart window options."

The researchers plan to perform more tests on the film to see if they can improve the technology even more.