A Zigzag Wall with Asymmetric Emissivity for Radiative Cooling Building Envelope

Abstract

Passive daytime radiative cooling (PDRC) is an attractive electricity-free approach to reducing energy consumption of buildings by reflecting sunlight and emitting infrared radiation (IR). Current PDRC research focuses on roofs, but limited attention has been paid to walls. Here, we report the control of angular asymmetry, a new degree of freedom, to realize zigzag PDRC walls with asymmetric emissivity and thus sub-ambient cooling performance. Such asymmetry leads to a daily average temperature drop of 2.3 °C compared to conventional walls coated with PDRC materials. When the ground is at ~56 °C, the temperature drop reaches 3.1 °C, corresponding to a relative cooling power of 67 W m^‑2 compared to the control wall. The zigzag wall can provide annual total energy saving up to 37 GJ (28.2 MJ m^‑2, ~15%), and annual total utility saving up to $1.4k (~22%) for a typical midrise apartment building, and benefit 42% population in the U.S., particularly in the southern warm areas.