Buried water-phase change material storage for load shifting: A parametric study

Abstract

Thermal energy storage systems based on phase change materials (PCM) are used to shift the peak load in buildings. An effective method to improve the performance of such system is to bury it in the soil to take advantage of soil's high thermal inertia. In this study, the model of underground buried water tank integrated with PCM panels as thermal accumulators is firstly proposed for a heat pump system. The study is conducted using an experimentally validated numerical model based on a heat balance approach using the effective heat capacity method. The performances of the buried water-PCM tank and an insulated water-PCM tank were compared to determine the improvement in the system efficiency as the results of soil's thermal inertia. A parametric study was also conducted to determine the optimal configuration and operating strategy of the buried water-PCM tank to satisfy the requirement of heat pump systems for load shifting. The outlet temperature, effective discharge duration (EDD), and total released heat were used as the indicators. The cooling capacity of the buried water-PCM tank is 24.96% higher than that of the insulated tank. The parametric study indicates that the parameters influencing the tank performance are the thermal conductivity of the PCM, length and width of the PCM panels, and heat transfer fluid velocity in the gaps between the panels. The study results are expected to serve as reference for the application of the newly proposed buried water-PCM tank in the underground engineering for load shifting.