Design and evaluation of a PCM heat accumulator applied in heating substations to accommodate supply-demand mismatch in district heating system

Supply-demand mismatch challenges the stable and reliable operation of heating systems with the increasing utilization of renewable energy. To solve this problem, this paper proposed a PCM heat accumulator applied in heating substations. First, a design methodology for the heat accumulator was proposed considering peak shaving of the heat source, the heat load of users, and the historical heating temperatures. Then, the numerical model of the heat accumulator was established and validated to evaluate its thermal performance. The effect of physical parameters of PCM, temperature of heat transfer fluid, porosity, and sphere diameter were researched. Finally, the influence of the PCM heat accumulator on the reduction of the discarded heat caused by the peak shaving of the heat source was calculated. The results show that the phase-change temperature has the most significant effect on the thermal performance of the heat accumulator. According to the historical heating temperature range, the optimal PCM is selected under the condition of constant flow rate and constant thermal power. Increasing the porosity or decreasing the sphere diameter is beneficial to the heat transfer process between PCM and heat transfer fluid. After installing the PCM heat accumulator, the discarded heat of the heating substation decreased by 63.21 %.