Beaming Heat into Space Could Make Your Air Conditioner More Efficient

Researchers all over the world are engaged in the search for better forms of energy as the demands of society continue increasing, but improving efficiency is necessary as well. Around 14 percent of total US energy production goes toward cooling homes and businesses, so that’s a good place to start. A company called SkyCool Systems is leveraging an interesting quirk of physics to improve cooling efficiency by beaming heat into space. All it takes is a very fancy mirror.

The mirrors designed by SkyCool Systems have the perplexing ability to be cooler than the surrounding air, and they don’t need power to do it. This is thanks to a counterintuitive property of radiant heat — something you’ve probably experienced without realizing it. Every object radiations heat energy in the infrared spectrum, which is a bit lower in energy than the visible red light we can see. We wear coats and gloves to bottle up as much of that energy as possible to stay warm during the winter, and the Earth’s atmosphere does the same thing. Well, unless the infrared radiation happens to be in a narrow sweet spot.

Scientists have long known that infrared radiation between eight and thirteen micrometers can escape into space with very little interference from the atmosphere. Some surfaces can emit this wavelength of radiation under certain circumstances — this is what causes a car window to form frost overnight even when the air temperature was above freezing. The challenge for SkyCool Systems is to harness this process in the light of day. Past attempts to use so-called “radiant cooling” during the day have been overwhelmed by the sun’s heat. The company seems to be succeeding with its highly efficient reflectors.

SkyCool Systems reports that it can keep its reflectors 8.8 degrees Fahrenheit (4.9 degrees Celsius) cooler than the surrounding air. In addition to emitting infrared energy in the right range to cut through the atmosphere, they also reflect 97 percent of sunlight to remain cooler. That’s obviously not going to replace your air conditioner, but it could make it much more efficient. Buildings could incorporate SkyCool Systems’ reflectors into the design; the reflectors offer an effective cooling efficiency of 40.1 watts per square meter. A Department of Energy-funded study in 2012 found that radiant cooling panels could cut cooling energy usage by 10-20 percent overall.

In its most recent publication, the company revealed it used narrow water pipes running under its panels to cool water by five degrees Celsius (about nine degrees Fahrenheit). That might make radiation cooling an easy augmentation for traditional air conditioning systems that use condensers (above). SkyCool Systems estimates a two-story office building could save up to 21 percent on its cooling bill with this technology.

SkyCool Systems isn’t talking about what radiant cooling might cost consumers, but it shouldn’t be too much. Other researchers have estimated similar systems could cost as little as 54 cents per square foot, and energy savings would cover the cost in as little as five years. SkyCool Systems hopes to start a large-scale demonstration of its technology with partners as soon as next year.