Dynamic and DoE-based assessment of a PVT-assisted ground-source heat pump system for cold-climate multi-family buildings

The electrification of residential heating in cold climates is limited by the reduced performance of heat pumps under low ambient temperatures. This work assesses the technical and economic performance of a Ground Source Heat Pump (GSHP) system integrated with Photovoltaic–Thermal (PVT) collectors for residential applications in cold climate conditions. The proposed configuration aims to increase the heat pump evaporating temperature, thereby enhancing efficiency during extreme winter operation. The system consists of PVT collectors, vertical borehole heat exchangers (BHs), and a heat pump sized to cover the building heating demand. The boreholes operate both as a heat source and as seasonal thermal energy storage. A control strategy is implemented to prioritize the direct use of PVT thermal output at the heat pump evaporator. When the heat pump is inactive, surplus thermal energy is injected into the ground and subsequently recovered during periods of simultaneous heat pump operation and low PVT thermal production. Dynamic simulations are carried out in TRNSYS 18. Borehole thermal behaviour is modeled using Type 557, accounting for ground thermal inertia and long-term temperature evolution induced by thermal charging and discharging. A residential multi-family building located in Oslo, Norway, is selected as a case study. The results indicate a substantial reduction in annual primary energy consumption, decreasing from 329.21 MWh/y in the reference GSHP system to 26.35 MWh/y in the proposed PVT–GSHP configuration, corresponding to a primary energy saving of 92%. The integration of PVT collectors also reduces grid electricity consumption and operating costs; however, the economic analysis highlights that the simple payback period remains relatively high (14.7 years) due to the current capital costs of PVT and geothermal technologies. A complementary Design of Experiments (DoE) analysis was performed by varying the PVT field size, the number of boreholes, the storage-tank volume, and the PVT activation threshold. Within this simulated domain, the PVT field size emerged as the dominant lever for primary energy savings and annual operating-cost reduction, whereas the borehole-field size mainly governed the minimum average borehole temperature and therefore the geothermal safety margin.