Radiative Cooling and Thermoregulation of Vertical Facades with Micropatterned Directional Emitters

TL;DR

This paper introduces a micropatterned directional emitter ({E}) that passively thermoregulates buildings by controlling thermal radiation, leading to significant energy savings and temperature regulation across seasons.

Contribution

The study presents a scalable, low-cost micropatterned directional emitter with tunable emittance, demonstrating its effectiveness for passive building thermoregulation in real outdoor conditions.

Findings

{E} reduces outdoor temperatures by 1.53-3.26b0C in warm weather.

{E} can be up to 0.46b0C warmer in cold weather.

{E} achieves cooling powers up to 40 W/mb2 and heating powers up to 30 W/mb2.

Abstract

We demonstrate a micropatterned directional emitter ({\mu}DE) with an ultrabroadband, azimuthally selective and tailorable emittance across the thermal wavelengths and over wide angles. The {\mu}DE can enable a novel and passive seasonal thermoregulation of buildings by reducing summertime terrestrial radiative heat gain, and wintertime loss. We show several types of {\mu}DE, such as metallic, white and transparent variants, made using low-cost materials and scalable manufacturing techniques that are already in large-scale use. Furthermore, we show that its directional emittance can be geometrically tailored to sky-view factors in different urban scenarios. Outdoor experiments show that {\mu}DEs stay 1.53-3.26{\deg}C cooler than traditional omnidirectional building envelopes in warm weather, including when they are sunlit. In cold weather, {\mu}DEs can be up to 0.46{\deg}C warmer. Additionally, {\mu}DEs demonstrate significant cooling powers of up to 40 Wm-2 in warm conditions and heating powers of up to 30 Wm-2 in cool conditions, relative to typical building envelopes. Building energy models show that {\mu}DEs can achieve all-season energy savings similar to or higher than those of cool roofs. Collectively, our findings show {\mu}DEs as highly promising for thermoregulating buildings.