Performance of photovoltaic thermal–ground source heat pump with a phase change water tank

Abstract

To address soil heat imbalance and seasonal energy efficiency degradation in photovoltaic/thermal-integrated ground source heat pump (PVT-GSHP) systems, this study proposes a five-mode dynamically switching PVT-GSHP system coupled with a water tank containing a phase change material (PCM). An office building in Zhengzhou is studied to develop a multi-mode simulation model incorporating heating, cooling, energy storage, auxiliary heating, and soil heat recharge modes through temperature differences and seasonal control. The performance of the PVT-GSHP system is evaluated by examining the effects of the PCM water tank on efficiency, power generation, energy consumption, and soil temperature. Additionally, the influences of the PVT collector area, water tank volume, buried pipe length, and installation inclination angle on energy consumption and power generation are analyzed. The PVT-GSHP system without PCM increased soil temperature by 42.60 % after 10 years of operation, whereas the coupled PCM system increased it by only 7.92 %, reducing the risk of soil thermal imbalance and proving its long-term operational stability. The introduction of the PCM tank also optimised the system’s energy efficiency, reducing the total annual energy consumption and lowering the heat pump COP decay rate by 51 %, while boosting the energy output by 231369.55 kW·h over 10 years. The PVT area is increased to 240 m² when the system becomes electrically self-sustaining, significantly improved energy matching during the winter heating season. A buried pipe length of 150 m reduces energy consumption by 12.3 % while limiting soil temperature fluctuations to 1.53 °C. The maximum power generation is achieved at an inclination angle of 30°, which is 5.2 % and 8.7 % higher than 15° and 75°, respectively. These findings provide a basis for mitigating seasonal energy efficiency degradation and soil heat imbalance in PVT-GSHP systems.