Study of Heat Transfer of Filling Body with Composite Phase Change Material in Seasonal Storage of Solar Energy

Solar energy is a free and promising renewable energy source. However, due to its intermittent problems, a heat accumulation unit is usually required to balance the seasonal differences between solar energy supply and heat energy demand. The filling technology can be used to form the heat energy accumulation unit and store or extract solar energy through a heat exchanger. An experiment and a simulation were carried out to study the heat accumulation and discharge process of a filling body with a heat accumulation unit in this study. The effects of the velocity of the heat transfer medium, the beginning temperature of the filling body, the heat accumulation and the discharge temperature, the heat accumulation and the discharge time ratio, and the additional proportion of CPCM on heat transfer performance were analyzed. The results show the following. The beginning temperature of the filling body has a greater impact on the heat accumulation capacity and a smaller impact on the heat discharge capacity. The heat accumulation capacity increases by 141% and the heat discharge capacity decreases by 10.6% when the beginning temperature decreases from 55 °C to 25 °C. The heat accumulation capacity increases with the rise of the heat accumulation temperature, and the heat discharge capacity has a large increase when the heat accumulation temperature is changed from 70 °C to 80 °C. The heat accumulation capacity of the first 200 min accounts for 83.3% of the heat accumulation capacity of the 400 min; in other words, the heat accumulation capacity can reach more than 80% at half of the heat accumulation time. The filling body with 20% additional CPCM stores 93.7% and discharges 55% more heat than the conventional filling body. The research results will provide guidance for the seasonal accumulation of solar energy using underground space and offer significant support for promoting sustainable energy solutions.