Integration of air-source to ground-source heat pump systems: Impact on borehole design and life-cycle cost in Canada

• The novel dual-source heat pump (DSHP) model is developed for three Canadian cities. • Transient ground-source heat pump (GSHP) and borehole behavior is captured. • DSHP reduces borehole length by up to 40 % compared to GSHP systems. • Life-cycle cost analysis reveals reduction of up to 8 % for Canadian climates. • DSHP economic feasibility is mainly dependent on drilling costs and heating loads. Dual-source heat pumps (DSHPs) mitigate high upfront costs of ground-source systems (GSHPs) by dynamically switching between air and ground sources. They might be a particularly feasible technology for climate with unbalanced heating and cooling loads that often result in large ground heat exchanger sizes, and consequently high capital costs and low community adoption, if only ground were to be used as a heat source/sink. This study proposes a framework to accurately evaluate the performance and economic advantages of adopting DSHP compared to GSHPs through semi-analytical dynamic simulations of DSHP system and life-cycle cost analysis. It then uses this framework to assess such advantages for DSHPs used in three Canadian cities (Edmonton, Toronto, and Montreal). By adjusting the outdoor air temperature set points, which determine when the heat pump switches from air-source to ground-source mode during heating and cooling modes, borehole lengths are reduced by up to approximately 40 % compared to GSHP-only designs. As a result, capital cost savings are achieved in Toronto and Montreal, while maintaining or improving life-cycle costs. Edmonton, in Climate Zone 6, shows limited overall savings.