A dynamic wall design with tunable angular emissivity for all-season thermal regulation

Radiative cooling achieves passive cooling by emitting long-wavelength infrared radiation (LWIR) to outer space. Increasing attention has been paid to radiative cooling walls in the building envelope. However, its undesired cooling effect in the winter exacerbates the heating demand of buildings. Here, we report a scalable wall design with dynamic rotatable fins (FinWall) to achieve tunable angular LWIR emissivity on the wall surface, enabling all-season thermal regulation. Field tests demonstrate that the FinWall yields a ∼2.0°C temperature elevation under cold weather and a ∼3.1°C temperature drop under hot weather compared to conventional high LWIR emissivity walls. This translates to extra power savings of 37 W m−2 for heating and 53 W m−2 for cooling. Further building simulations indicate that a mid-rise apartment building equipped with FinWalls can save 24% (or 10%) annual energy versus the same building with high-emissivity walls (or low-emissivity walls) in the US.