A cost-effective dual-mode PCM with a sandwich structure for year-round building energy conservation

Traditional thermal insulation materials cannot absorb and store cosmic cold energy in summer and solar energy in winter, which severely restricts building energy saving and carbon emissions reduction. Hence, this study prepared a low-cost and scalable dual-mode phase change material (PCM) based on melt blending. The two sides of dual-mode PCM are SEBS/PW/ZnO and SEBS/PW/EG, which perform radiative cooling (RC) and photothermal conversion (PC), respectively. And the middle layer is SEBS/PW, which prevents materials cross-penetration between two sides. Adding nano-ZnO significantly improves the reflectance of RC side of dual-mode PCM from 0.49 to 0.87. Moreover, the dual-mode PCM has an absorption of 0.92 at PC side,a high enthalpy of 176.9 J/g, along with excellent thermal stability and hydrophobicity. More importantly, its cost is only 21.2 CNY/kg, lower than that of conventional flexible PCM (21.4 CNY/kg). And the dual-mode PCM has better heat insulation/gain performance. Compared with conventional flexible PCM, dual-mode PCM achieves a peak temperature drop of 21.2 °C in summer and an average temperature rise of 2.6 °C in winter. Furthermore, simulation shows that except for Kunming, both absolute and relative energy saving of dual-mode PCM increase with decreasing latitude. The dual-mode PCM performs best in Wuhan and Guangzhou, with close annual energy savings of 3.13 and 3.21 kWh/m2 and low payback periods of 6.7 and 6.5 years. Overall, the dual-mode PCM strikes an excellent balance between performance and cost, which is a viable solution building energy saving.