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New material efficiently cools buildings by radiating heat into outer space

Cooling material

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(NaturalNews) Stanford University researchers say they have developed a reflective material that can successfully cool buildings by hurling their heat into the vacuum of space, according to a study published in the journal Nature on November 26.

"Every object that produces heat has to dump that heat into a heat sink," co-author Shanhui Fan said. "What we've done is to create a way that should allow us to use the coldness of the universe as a heat sink during the day."

"The coldness of the universe is a vast resource that we can benefit from," Fan said. The researchers noted that, because the system works without electricity, it could produce enormous energy savings.

Air conditioning accounts for approximately 15 percent of all U.S. energy usage.

Miracle material cools down in sunlight

The new cooling material consists of seven layers of silicon dioxide and hafnium dioxide, atop a thin layer of silver. The entire layered material is just 1.8 microns thick; in contrast, a human hair averages approximately 100 microns in width.

The layers have been engineered to different widths, allowing them to bend and reflect different wavelengths of electromagnetic radiation in both the visible and infrared spectra.

Most of what we think of as "heat" is actually objects dumping infrared radiation.

"If you use an infrared camera, you can see we all glow in infrared light," Fan said.

In tests, the cooling material successfully reflect 97 percent of solar radiation, thereby preventing the sun from transferring heat into the building. This is a major improvement over other passive cooling materials, which typically function only at night.

Importantly, the new material is designed in such a way that it reflects solar radiation only at infrared wavelengths that cannot be absorbed by the air. This means the radiation bounces off the material and shoots straight back into space.

"These guys have pushed the limits with some clever optical engineering," said Geoff Smith, an applied physicist at the University of Technology in Sydney, Australia.

With solar radiation removed as a heating factor, a building covered in this material would be more likely to assume the temperature of its surroundings. When the researchers tested a prototype of the material on a clear winter day, they found that, when placed in sunlight, it cooled to almost 9 degrees Fahrenheit (5 degrees Celsius) below the ambient air temperature.

"Something that cools down rather than heating up in the sun is counterintuitive, but that's what the device is designed to do," said Fan.

"Extraordinarily simple"

Preliminary tests suggest that the cost of producing the material is similar to the costs of electrical cooling. There is no reason it could not be used in conjunction with air conditioning, they noted, including air conditioning powered by solar technology.

In addition to reducing energy consumption, the new material could also enabling cooling in remote regions without access to electricity, the researchers suggested.

"This is very novel and an extraordinarily simple idea," said Eli Yablonovitch, a photonics crystal expert at the University of California, Berkeley, who was not involved in the study.

Several key steps remain, however, before the new material could become widely used. A 1.8-micron-thick material is likely too delicate to be used to coat a building or rooftop, which means that the material may need to be given a structural backing. In addition, the researchers need to figure out how to deal with heat generated within a building, not just outside it.

Most significantly, the researchers need to build and test a larger model; the prototype is only about 8 inches across.

"We are now scaling production up to make larger samples," Fan said. "To cool building[s], you really need to cover large areas."






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