Scalable Temperature-Adaptive Radiative Cooler for Thermal Regulation

The wavelength range of the mid-infrared atmospheric window matches that of thermal radiation near room temperature, thus the sky is used as a natural heat sink for passive radiative cooling of houses. For decades, experiment works in the field have focused on using static, cooling-optimized material properties to maximize the radiative cooling power of roof coating. However, in cold nights or winter times, especially in climates where heating dominates house energy consumption, the resultant overcooling exacerbates the heating cost and causes more energy consumption over the year. Here we present a different approach to thermal regulation by developing a mechanically flexible and energy-free temperature-adaptive radiative coating (TARC) to minimize the total energy consumption throughout the year, rather than only on hot days. The TARC is a metasurface that optimally absorbs solar energy and automatically adapts its thermal emittance to different ambient temperatures, driven by a photonically amplified metal-insulator transition. We demonstrate its performance in thermal regulation for energy-saving through simulation, lab characterization, and field tests.<br/>Simulations based on real climate data show that TARC outperforms existing roof coatings in yearly energy saving in most climates, especially those with substantial seasonal variations. We also develop a scalable process to print TARC in large sizes and at low cost. The scalable fabrication makes TARC a promising product for thermal regulation in other systems such as spacecraft and tents.<br/><br/>Reference:<br/>Tang, Kechao, et al. Science 374.6574 (2021): 1504-1509.