Reversible solar heating and radiative cooling coupled with latent heat for self-adaptive thermoregulation

Abstract

Passive solar heating and radiative cooling attracted lots of attention in global energy consumption reduction due to their unique electricity-free advantage. However, static single radiation cooling or solar heating would lead to over-cooling or over-heating in cold or hot weather, respectively. How to achieve effective self-adaptive thermoregulation is critical for dynamic thermal management. Hence, in this work, a self-adaptive thermoregulation strategy was designed by coupling latent heat storage or release with reversible solar heating and radiative cooling. A commercial memory alloy could realize self-adaptive thermoregulation at the critical temperature between radiative cooling with high solar reflectance R¯solar = 0.95 and thermal emittance ε¯LWIR = 0.93, and solar heating with high solar absorptance α¯solar = 0.92 and low thermal emittance ε¯IR = 0.08. High thermal conductive phase change material could further improve the thermoregulation performance with a latent heat of ∼136 J g−1, and thermal conductivity of 3.4 W m−1 K−1, resulting in a superior heating performance than the single solar heating (39.9 vs 36.9 °C) and superior cooling performance than the single radiative cooling (33.8 vs 35.5 °C). The maximum heating temperature increase could be 12.7 °C in the cold situation, and the temperature drop could be 8.3 °C in the hot situation. Energy consumption calculation showed that the designed sample could save 68%–90% of annual energy consumption compared with the common roof, indicating that coupling spectral regulation with the latent heat can greatly improve the self-adaptive thermoregulation performance and save the total energy consumption in thermal management.