This Incredible Building Material Shoots Heat Into Space (So Buildings Need Less AC)

What if—instead of keeping our buildings cool from the inside—the heat just bounced off them back to where it came from?

There’s a big renewable energy resource we’ve yet to exploit: the cold of the universe.

That’s according to Aaswath Raman, a researcher with the Ginzton Laboratory, at Stanford University. What he means is the capacity of space to be a “thermodynamic resource,” helping us Earthlings to be more energy-efficient. Raman is working on a building material that’s ultra-reflective to the sun’s rays, and able to bounce significant amounts of heat so far away from buildings that it goes beyond the atmosphere.

The technology—passive cooling that works during the daytime—could help reduce the need for wasteful air conditioning. Currently, A/C accounts for 15% of all primary U.S. electricity demand, an enormous amount considering all the other things we use electricity for.

The material exploits the way that all objects throw off heat as infrared radiation. Some of this unseeable light is trapped within the atmosphere, all the more so because of greenhouse gas emissions. But some heat also goes into the upper atmosphere, where it’s dispersed into an enormous heat sink: the freezing cold vacuum of space. Raman’s coating—made up of seven layers of silicon dioxide and hafnium oxide and a layer of silver—does two things. First, it’s able to send the infrared at a particular frequency so that it leaves our atmosphere. And second, it reflects 97% of sunlight, stopping buildings from heating up in the first place.

“The challenge was to continue to send out this heat as infrared light, or radiation, but at the same time not be heated up by the sun,” says Raman.

Read more: This Incredible Building Material Shoots Heat Into Space (So Buildings Need Less AC)

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