On daytime radiative cooling using spectrally selective metamaterial based building envelopes

Recent developments in metamaterials made daytime radiative cooling possible, by engineering material surfaces to achieve high emissivity in the 8-13 mu m 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/m(2), the RC-film model house achieved a roof surface temperature of consistently 2-9 degrees 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 degrees 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 degrees C cooler roof temperature and a 4-12 degrees 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/m(2) during the testing days. (C) 2021 Published by Elsevier Ltd.

Automated summary

Recent advancements in metamaterials have enabled daytime radiative cooling by enhancing the emissivity in certain wavelengths and reflectivity in others. This study demonstrated the passive cooling of a full-scale model house using a scalable polymer-based spectrally selective metamaterial, achieving significantly lower temperatures both on the roof surface and indoors compared to traditional metal sheet houses. The RC-film envelope showed a substantial reduction in heat influx, with an aggregated radiative cooling power ranging from 5 to 55 W/m(2) during testing days, marking a new milestone in energy-efficient cooling technology.