Stanford researchers, including one of Indian-origin, have developed a revolutionary ultrathin coating material that can help cool buildings by radiating heat away from them and sending it directly into space.
The ultrathin, multilayered material, developed by a team led by electrical engineering Professor Shanhui Fan and research associate Aaswath Raman deals with light, both invisible and visible, in a new way.
Invisible light in the form of infrared radiation is one of the ways that all objects and living things throw off heat. This invisible, heat-bearing light is what the Stanford invention shunts away from buildings and sends into space.
The new material is also a stunningly efficient mirror that reflects virtually all of the incoming sunlight that strikes it, researchers said.
The material is just 1.8 microns thick, thinner than the thinnest aluminum foil.
The material allows for 'photonic radiative cooling' - a one-two punch that offloads infrared heat from within a building while also reflecting the sunlight that would otherwise warm it up.
This paves the way for cooler buildings that require less air conditioning, researchers said.
The researchers said they designed the material to be cost-effective for large-scale deployment on building rooftops.
The coating radiates heat-bearing infrared light directly into space. It sends this infrared light away from buildings at the precise frequency that allows it to pass through the atmosphere without warming the air, a key feature given the dangers of global warming.
This multilayered coating also acts as a highly efficient mirror, preventing 97 per cent of sunlight from striking the building and heating it up.
"We've created something that's a radiator that also happens to be an excellent mirror," said Raman.
Together, the radiation and reflection make the photonic radiative cooler nearly 9 degrees Fahrenheit cooler than the surrounding air during the day.
Making photonic radiative cooling practical requires solving at least two technical problems.
The first is how to conduct the heat inside the building to this exterior coating. Once it gets there, the coating can direct the heat into space, but engineers must first figure out how to efficiently deliver the building heat to the coating.
The second problem is production. Currently the Stanford team's prototype is the size of a personal pizza. Cooling buildings will require large panels.
The researchers said there exist large-area fabrication facilities that can make their panels at the scales needed.
The study is published in the journal Nature.
