Feasibility and performance of coupled air-ground source heat pump systems with thermal storage

Harnessing thermal energy from ambient air to maintain a balanced heat extraction and release from the soil throughout the year can potentially improve the performance of ground source heat pump systems. This paper proposes and analyzes a specific configuration a coupled air-ground source heat pump system. The focus of this study is to investigate the impact of climatic variations on the feasibility of the system, as well as to analyze the economic and environmental benefits associated with the inclusion or exclusion of a thermal energy storage device. The results show that in cold regions, the ground serves as the primary heat source for heat pumps, whereas during transitional seasons, air energy is mainly utilized to transfer heat directly to the soil. As the climate warms, the fraction of heat supplied by air gradually increases, reducing electrical consumption by up to 17 % compared to the conventional air source heat pumps. Despite the negative impact of thermal energy storage on the coefficient of performance, it is still advantageous as it decreases the electricity consumption during peak price periods, leading to at least a 20 % reduction in life cycle costs in most regions. Additionally, the coupled air-ground source heat pump system is more competitive than air source heat pump systems in scenarios with longer design life, colder climates, and lower borehole heat exchanger costs.