On daytime radiative cooling using spectrally selective metamaterial based building envelopes

Abstract

Recent developments in metamaterials made daytime radiative cooling possible, by engineering material surfaces to achieve high emissivity in the 8–13 μm atmospheric window and high reflectivity elsewhere. In this study, we demonstrated a daytime radiative cooling application using a scalable polymer-based spectrally selective metamaterial (named Radiative Cooling film (RC-film)) to passively cool a full-scale model house. When exposed under direct solar irradiation peaking 720 W/m2, the RC-film model house achieved a roof surface temperature of consistently 2–9 °C below the ambient during a continuous 72-h experiment period. Further, setting a new milestone, the indoor air temperature of the RC-film house was also consistently 2–14 °C below the ambient during the daytime. This implies that the RC-film envelope had achieved a de facto cooling effect on the indoor space without active energy consumption. Compared to a metal sheet house, the RC-film house achieved a 25–30 °C cooler roof temperature and a 4–12 °C cooler indoor temperature during the daytime. For the South wall where the most solar radiation was received, the RC-film envelope demonstrated a 60–70% heat influx reduction. The entire exposed envelope as a whole achieved an aggregated radiative cooling power ranges from 5 to 55 W/m2 during the testing days.