Huang, LiLiHuangPiontek, UdoUdoPiontekZhuang, LuluLuluZhuangZheng, RongyueRongyueZhengZou, DeqiuDeqiuZou2025-09-092025-09-092025https://publica.fraunhofer.de/handle/publica/49505610.1016/j.est.2025.118301A solar cooling and heating plant equipped with a 1000 l hot water storage tank, operational since 2018, exhibited performance instability in its absorption chiller due to frequent start-up and shutdown cycles and a low solar fraction (SFn) of 50.9 % during the cooling period. To address these issues, a high-efficiency latent heat storage using phase change material (PCM) was developed for retrofitting the plant. Key factors affecting the heat transfer performance, including the PCM thermal conductivity, melting point, and the storage configuration were systematically investigated through numerical simulations. Based on the average charging and discharging temperatures of the hot water storage in 2021, a PCM with a melting peak point of 64 °C (RT64HC) was selected after comparison with PCMs having melting points of 62 °C and 70 °C. To further enhance thermal conductivity, the PCM was modified with 8 wt% expanded graphite (EG), achieving a balance between charging/discharging rates and storage capacity. The engineered storage design featured a shell-and-tube heat exchanger with 308 tubes filled with RT64HC/EG8% and water circulating on the shell side to ensure efficient heat transfer. After implementation in late 2021, the system reduced the chiller's switch-on frequency by 33.5 %, and improved the solar fraction to 75.6 % during the cooling period.ensolar coolingsolar heatingphase change material (PCM)numerical simulationHeat Transfer Simulationshell-and-tube heat exchangerjournal article