On the proper integration of pre-heating tanks in ground source heat pump systems combined with photovoltaic-thermal panels

Ground Source Heat Pump (GSHP) systems are an energy-efficient solution for meeting heating demands in buildings. However, in cold climates with heating-dominated loads, the net extraction of heat from the ground causes a thermal imbalance, reducing ground temperature and the seasonal performance factor (SPF) of the heat pump over time. Photovoltaic-thermal (PVT) panels can help regenerate ground temperature, improving energy efficiency and potentially reducing the required borehole field size. While the scientific literature has recently clarified the design and potential of GSHP + PVT, limited research has been done on the use of pre-heating tanks to improve the system performance. This study evaluates three GSHP + PVT system layouts using TRNSYS simulations for a multi-family house in Oslo over a 50-year period. The results show that integrating a preheating tank on the condenser side increases the 50-year-averaged system SPF4 from 3.85 (baseline) to 4.11 (+6.8 %), demonstrating enhanced energy efficiency. However, the SPF4 reduction over time is larger with the pre-heating tank (-7.47 %) due to reduced ground regeneration. In contrast, placing the pre-heating tank on the evaporator side yields a moderate SPF4 increase to 3.95 (+2.6 %). Additionally, the optimal configurations lead to a 3.6 % reduction in electricity import from the grid, while the impact on PVT electricity generation remains minimal. These findings highlight that pre-heating tanks can effectively enhance GSHP + PVT efficiency, but their placement must be carefully considered to balance short-term efficiency gains with long-term performance.