Beyond cooling: Radiative thermoregulation in the Earth's glow with micropatterned directional emitters

We demonstrate a micropatterned directional emitter (μDE) with an ultrabroadband directional thermal emittance. The μDE enables a previously unexplored passive seasonal thermoregulation of buildings by reducing terrestrial heat flows. μDEs with metallic and white appearances can be made using low-cost materials and scalable manufacturing techniques and have their directional emittance geometrically tailored to different urban scenarios. We also show a novel, visibly transparent variant. In outdoor experiments, μDEs stay 1.53°C to 3.26°C cooler than traditional omnidirectional building envelopes in warm weather and up to 0.46°C warmer in cold weather. Additionally, our μDEs demonstrate significant cooling powers of up to 40 W.m⁻² in warm conditions and heating powers of up to 35 W.m⁻² in cool conditions relative to typical building envelopes. A building energy model shows that μDEs can achieve all-season energy savings similar to or higher than those of cool roofs. Collectively, our findings show μDEs as highly promising for thermoregulating buildings.