http://www.technologyreview.com/news/532826/material-cools-buildings-by-sending-heat-into-space/[font face=Serif][font size=5]Material Cools Buildings by Sending Heat into Space[/font]
[font size=4]A new material that requires no electricity uses the universe as a heat sink—even when the sun is shining.[/font]
By Katherine Bourzac on December 1, 2014
[font size=3]A material that simultaneously reflects light and radiates heat at frequencies that vent it through the Earth’s atmosphere could one day help cool buildings on hot days. The material cools itself to a temperature below the ambient air, and has been tested on a rooftop at Stanford University by its inventors, who are now working on scaling up the design.
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Usually the way to let something cool off is to put it somewhere cold; the hot object will radiate its excess heat into the surroundings. Fan’s material becomes cooler than its surroundings by reflecting light and emitting heat at carefully tuned frequencies. The material emits heat at frequencies that match the planet’s “thermal window”—from eight to 13 micrometers—which lets it pass through the atmosphere and into space. It effectively cools down by using outer space as a heat sink.
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To demonstrate the weird properties of this layered material, the Stanford researchers compared it to silicon painted black—a good thermal radiator—and aluminum—a good reflector. The passive cooler design is described today in the journal
Nature.
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Fan says covering an entire roof with the material should eliminate the need for air conditioning. The group plans to leverage manufacturing technology that’s used to make coated windows, and it might be possible to make the material, which is only about two micrometers thick, on lightweight plastic films for easier installation. But the next step is a modest one: they’ll to go from the eight-inch demo to a square-meter tile of the material.[/font][/font]
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