Experimental and simulation studies of the temperature adaptive radiative cooler with a phase change material cover

Passive daytime radiative cooling (DRC) technology has demonstrated energy-saving potential in buildings. However, it also meets a challenge in countering extra heat loss during the heating season. To solve this problem, a temperature-adaptive switch cover (TASC) was developed with phase change material (PCM) of paraffin. Then TASC was integrated with a multilayer DRC
(polydimethylsiloxane-SiO2-Ag) as temperature-adaptive radiative cooler (TARC) and then tested in different seasons. The experimental results revealed that the TARC system showed similar cooling effects to static DRC in the cooling season when the ambient temperature is above 20℃. This is because TASC was kept in a "switch-on" state, the average daytime cooling down temperature performance of TARC and DRC was at 4.8℃ and 5℃. However, the TARC achieved an average temperature higher than the ambient temperature during the daytime in winter, while DRC still showed all-day cooling. This is due to the increased sunlight absorption by the TASC when it was switch-off. Furthermore, this research established a numerical model of TARC and has it verified with experimental data. We also optimized the structure of TARC with a thinner TASC and theoretically evaluated its thermal performance under the same climate conditions of the two days experiments. The simulation results show that the optimized TASC has enhanced temperature adaptability of the TARC system. The average daytime temperature drops that TARC achieved in the cooling season is enlarged by 0.2°C, while the average daytime temperature in the heating season is 0.99°C higher than the ambient temperature.