Reflecting Building Heat into Space

A device developed by Stanford University scientists called a photonic radiative cooler could provide a zero-energy solution to building cooling by radiating infrared heat from facilities into outer space. Not only can the device radiate existing heat but it also acts as a mirror, reflecting 97% of sunlight away from buildings to help reduce the amount of cooling needed in the first place. With the DOE reporting that up to 15% of energy used in U.S. buildings is for air conditioning, the new device could help make big energy gains without compromising interior comfort. 

Passive Radiative Cooling Below Ambient Air Temperature Under Direct Sunlight, published in Nature, shows that when the device is exposed to direct sunlight greater than 850 watts per square meter on a rooftop, the photonic radiative cooler can keep the air 4.9 degrees C. below ambient air temperature, with 40.1 watts per square meter of cooling power. 

Also key to the design is specific tuning to reflect heat through an existing transparency window, ensuring that radiated heat is not trapped in the atmosphere but sent all the way to space. The scientists estimate that use of their photonic radiative cooler on a typical roof could provide passive cooling equivalent to 120,000 kWh annually.