A novel flexible dual-mode phase change material for year-round energy saving

The film/coating with dual-mode of photothermal conversion (PC) and radiative cooling (RC) has limited heat storage capacity and cannot achieve continuous heating/cooling. Due to its high heat storage density, phase change material (PCM) can store heat/cold to continuously utilize thermal energy. Hence, this study prepares a novel flexible PCM with dual-mode of with PC and RC. The dual-mode PCM has an extremely high enthalpy of 208.7 J/g, and low thermal conductivity of 0.23 W/(m·K). In PC mode, the solar absorptivity reaches 0.94. In RC mode, the solar reflectance is 0.91, and the emissivity in atmospheric window is 0.92. The comparative experiments of dual-mode PCM and dual-mode melamine foam (MF) film were conducted to demonstrate superiority of radiation heating/cooling combined with PCM. In PC mode, the photothermal conversion efficiency of dual-mode PCM reached 90.5 %, while the photothermal conversion efficiency of dual-mode MF film was only 33.4 %. Moreover, under outdoor heating experiment with cover shield, the dual-mode PCM made its temperature always higher than ambient temperature at night, while the dual-mode MF film cannot. Even if the cover shield was removed, the dual-mode PCM still reduced the energy consumption by 4.0 % compared to the dual-mode MF film. Besides, in RC mode with cover shield, the dual-mode PCM achieved a peak temperature drop of 6.1 °C relative to the dual-mode MF film. In RC mode without cover shield, the dual-mode PCM achieved energy saving of 63.3 % compared with dual-mode MF film. In summary, the dual-mode PCM has more continuous heating/cooling performance than the dual-mode film, thereby achieving more significant energy saving.