A high performance and ultra-low cost radiative cooling phase change material: Fabrication, experiment and simulation

Abstract

Radiative cooling phase change material (RC-PCM) achieves efficient passive cooling, offering great promise for building energy saving and carbon reduction. However, constrained by complex preparation and high costs, the RC-PCMs have yet to achieve large-scale application. Hence, this study incorporated nano-Al2O3 into the phase change hydrogel by melt blending, thereby preparing an RC-PCM. The RC-PCM exhibits a high reflectivity of 0.918, a relatively high emissivity of 0.842, and a remarkable volumetric enthalpy of 245.6 J/cm3, accompanied by excellent thermal stability and flexibility. Compared with previous studies, the RC-PCM offers comparable or even superior optical-thermal properties at an ultra-low cost of 0.68 USD/kg, achieving a significant cost saving of 78.3%–99.4%. Moreover, in outdoor experiments, the RC-PCM maintains sub-ambient cooling for 90.3% of daytime, showing great cooling performance. Simulations were conducted for typical cities across five climate zones in China. The RC-PCM saves energy by 3.19 kWh/m2 in Guangzhou and 1.98 kWh/m2 in Wuhan, whereas the reductions in other cities do not exceed 0.21 kWh/m2. Moreover, the annual energy savings and carbon emission reductions show little dependence on RC-PCM thickness, whereas the payback period scales roughly linearly with it. For 1-mm-thick RC-PCM in Wuhan and Guangzhou, the payback periods do not exceed 4.0 years for cost and 1.3 years for carbon, respectively. Overall, the RC-PCM combines superior optical and thermal properties with easy fabrication and ultra-low cost, enabling scalable application in hot summer and warm winter as well as hot summer and cold winter climate zones.