A new record for cooling using a technique called radiative cooling, which blasts heat into space, is reported in Nature Communications this week. The cooling device is shown to lower temperatures of small objects by up to 42°C. Although the present set up is not capable of large-scale applications, such as air conditioning of buildings, the findings demonstrate the potential for radiative cooling to achieve large reductions in temperatures.

Cooling of various objects, such as computers, consumes a lot of energy and new solutions are needed to reduce the amount of energy used. One potential method is radiative cooling, which relies on a transparency window in the Earth’s atmosphere through which heat radiation at a specific frequency can be emitted into the cold darkness of space. Shanhui Fan and colleagues produce a radiative cooling device that can cool to at least 33°C lower than ambient temperature, with a maximal reduction of 42°C during exposure to sunlight. Previous demonstrations of radiative cooling have only achieved temperature reductions of around 5°C during the daytime, and 15-20°C at night time.

A highly selective thermal emitter to release heat into space via the transparency window is key to the record-setting performance of the radiative cooling apparatus, the authors report. The authors also describe theoretical analyses that suggest temperature drops of up to 60°C below ambient temperatures might be possible.