Window coating rejects up to 70% of incoming solar heat

MIT engineers have developed a heat-rejecting film that could be applied to a building’s windows to reflect up to 70 per cent of the sun’s incoming heat. Their invention could lower energy bills by reducing the need for air conditioning.

According to an MIT statement, air conditioners are responsible for some 6 per cent of all the electricity produced in the US – a figure that’s sure to grow as global temperatures rise.

To help keep energy consumption down, MIT researchers have now developed a see-through film or coating that can reject up to 70 per cent of incoming solar heat.

The film resembles transparent plastic wrap and is embedded with microparticles made from a type of phase-changing material that shrinks when exposed to temperatures of 29.5 degrees Celsius and higher. In higher temperatures, the microparticles give the normally transparent film a more translucent or frosted look.

When applied to windows in the summer, the film could passively cool a building while still letting in a good amount of light. The researchers estimate that if every exterior-facing window in a building were covered in this film, the building’s air conditioning and energy costs could drop by 10 per cent.

Nicholas Fang, a professor of mechanical engineering at MIT, says the material is an affordable and energy-efficient alternative to existing smart window technologies.

“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 says. “We thought there might be room for new optical materials and coatings, to provide better smart window options.”

The film was developed in collaboration with researchers at the University of Hong Kong, who are keen on finding ways to reduce energy consumption in buildings in a city that has committed to reduce its total energy use by 40 per cent by the year 2025.

Image courtesy of the researchers

Andrea Schaller

Founder and editor Go4Ges

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