New material cools vertical surfaces, aids energy conservation

On Friday, researchers from the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences published their work on reflective surfaces in the international journal Science.

The team has demonstrated a hierarchically designed, angularly asymmetric, spectrally selective thermal emitter that efficiently reflects sunlight and reduces the absorption of thermal radiation from the atmosphere and hot ground, achieving a cooling effect below ambient temperature.

On scorching summer days, people seek refuge in cool and pleasant air-conditioned rooms, but cooling devices like air conditioners consume massive amounts of energy, exacerbating greenhouse gas emissions and driving global warming.

Faced with this challenge, the team led by Li Wei has explored an effective solution that requires no energy consumption.

According to their research, subambient daytime radiative cooling enables temperatures to passively reach below ambient temperature, even under direct sunlight, by emitting thermal radiation toward outer space.

Previous demonstrations of subambient daytime radiative cooling required surfaces that directly faced the sky and couldn't be applied to vertical surfaces, such as the side of a building. The team's new material is able to do just that.

Their emitter can reach a temperature about 2.5 C below the surrounding temperature. Its reduction is about 4.3 C and 8.9 C cooler than a silica-polymer hybrid radiative cooler and commercial white paint, respectively.

The research has achieved subambient daytime radiative cooling on vertical surfaces, holding implications for the practical application of radiative cooling, energy conservation and emission reduction efforts, the team said.