Comparing regeneration and bivalent strategies for ground-source heat pumps in heating-dominated buildings

• Hybrid ground source heat pumps are compared in terms of cost and performance. • Solar thermal collectors maintain high system performance with fewer boreholes. • Series-connected dry coolers allow compact ground fields with long-term stability. • Photovoltaic-thermal systems are ideal where electricity cost is relatively high. • Air source heat pump and parallel dry coolers offer lower thermal stability. Ground-source heat pump systems are energy-efficient solutions for buildings located in cold, heating-dominated climates. This study explores how incorporating additional heat sources or regeneration techniques can improve the ground thermal imbalance, either by reducing the reliance on the borehole field or by injecting heat into the ground, respectively. The contribution of this study lies in conducting a comprehensive, long-term techno-economic comparison of six hybrid ground-source heat pump system layouts, including regeneration-based and bivalent configurations, under identical boundary conditions for a Nordic climate. The configurations evaluated in this study integrate ground-source heat pump systems with either solar thermal collectors, photovoltaic-thermal collectors, dry cooler (in series or parallel configurations), or an air source heat pump. Using TRNSYS simulations over a 20-year period for a multi-family house in Oslo, Norway, the results indicate that solar-assisted ground-source heat pump configurations, including those integrated with photovoltaic-thermal or solar thermal collectors, significantly reduce the annual net ground heat extraction, with solar thermal achieving the highest regeneration capability by reducing net heat extraction by up to 73.8 %. Similarly, the dry cooler in a series configuration demonstrated strong performance, reducing net ground heat extraction by 57.7 %. In contrast, layouts that primarily reduce the ground dependence, such as the dry cooler in a parallel configuration and the air source heat pump, exhibited lower ground thermal stability, with the air source heat pump showing the least effective ground thermal balance. From the total cost perspective, the dry cooler in a series configuration appears to be one of the most cost-effective solutions. For example, it can reduce the total costs by up to 9.91 % over 20 years while approximately maintaining the system’s energy efficiency. Photovoltaic-thermal shows benefits, but with lower performance than solar thermal, due to higher investment costs and lower thermal efficiency, not compensated by its electricity production. In contrast, the air source heat pump and the dry cooler in a parallel configuration showed minor economic benefits. In large-scale installations, where the borehole field is more compact and the thermal interaction increases, the results show that layouts incorporating regeneration strategies achieve better performance and cost-effectiveness compared to those that only reduce the reliance on ground extraction.