Angle-selective thermal emitter for directional radiative cooling and heating

Abstract

Material emissivity engineering can boost energy efficiency in cooling and heating systems by tailoring radiative heat exchange. However, practical energy saving often faces challenges due to environmental temperature inhomogeneity, such as building walls encountering both cold sky and hot ground in the summer. Matching the inhomogeneous temperature requires angle-selective emissivity materials. We present a micro-wedge structure for directional thermal emission control. Our design shows a large broadband contrast in directional emissivity (0.9–0.1), with the angular emission range controlled by the micro-wedge geometry and tunable through magnetic coupling. The angle-selective emitter offers better daytime radiative cooling for outdoor vertical surfaces (2°C below isotropic emitters), potentially saving 10%–40% cooling energy, and efficient indoor radiant heating. Harnessing the directional characteristic of thermal emission opens new opportunities in energy efficiency enhancements across various applications, such as space heating and cooling, waste heat recovery, and solar thermal power generation.