Home Cooling Without Electricity? An Air Conditioning Breakthrough

With winter upon us, air conditioning is probably the last thing most people (at least in the Northern Hemisphere) are thinking about. However, winter won't last forever, and with climate change pressing in, many regions are expected to suffer from hotter and hotter summers. Now, a team of researchers has dreamed up a new way to cool a room without escalating energy demands.

According to the team of physicists and engineers, past surveys have shown that as much 15 percent of the energy used in buildings in the United States is spent powering air conditioning systems. As only a seasonal cost, that may not seem like much, but it's important to remember that a great portion of US electricity comes from coal-based power plants - a hefty source of man-made carbon emissions, which in turn drive net warming.

To prevent a warming climate from leading to more energy consumption, research leads Shanhui Fan and Aaswath Raman have focused their efforts on developing home cooling technology that does not exacerbate energy demands.

Their latest energy-saving breakthrough is detailed in a study published in the journal Nature.

According to the study, the team invented a way to encourage buildings to dump their heat without the need for pumps and compressors. Instead, they simply radiate it into outer space using a material that takes advantage of something called thermal photonics.

"This is very novel and an extraordinarily simple idea," Eli Yablonovitch, an engineer and pioneer of photonics, explained in a recent release. "As a result of professor Fan's work, we can now [use radiative cooling], not only at night but counter-intuitively in the daytime as well."

So how exactly does this work? According to the researchers, in principle, to cool a building all you need to do is pull infrared radiation from it. This is the same invisible radiation you feel when standing in front of an oven, and is also the root of sunlight's warmth. The photonic material interacts with light much like a semiconductor affects electricity, where the energy levels of infrared light are converted and then expelled.

In what the researchers are calling a "one-two punch" to heat, the material also is exceptionally good at reflecting sunlight, preventing new infrared radiation from re-heating a building. (Scroll to read on...)

"We've created something that's a radiator that also happens to be an excellent mirror," Raman said, explaining that the multi-layered material that they have been testing not only sounds good on paper, but has shown promise in tests.

According to the study, the current prototype material reflects 97 percent of sunlight while radiating at a wavelength at which our atmosphere is most transparent (13 microns). This allows the material to send heat straight into space without trapping it just above our heads.

"Every object that produces heat has to dump that heat into a heat sink," Fan explained. "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."

Initial tests have revealed that, when isolated, the radiation and reflection make the photonic material nearly nine degrees Fahrenheit cooler than the surrounding air during the day. If applied to the surface of a building, this difference would disappear, but the resulting balance would slightly cool its surroundings.

Of course, compared to Central Air, a "slight cooling" on a hot summer day is certainly not enough. However, scaled-up use of this material would help mitigate some costs, even while researchers pursue ways to improve this cooling effect.

"I am personally very excited about their results," added Marin Soljacic, a physicist at the Massachusetts Institute of Technology.

Solijacic explained that this breakthrough has even wider implications than just air conditioning, as it showcases how the world can use the cold Universe as a nearly unlimited expanse in which to dump heat.

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