ASHRAE ST-16-027

Abstract

Scope: This paper discusses a technical comparison of a directexpansion ground-source heat pump (DX-GSHP) and an airsourceheatpump( ASHP).Tolowerthegroundheatexchanger size for cost reduction purposes, the system performance of a hybrid system is also evaluated using a supplementary air evaporator combined with the DX-GSHP. Detailed screening models previously developed for ASHPs and DX-GHSPs are first used to compare the seasonal performance of these two options for a residential building in the cold-climate city of Montréal, Canada. Then, the model is adopted for performance evaluation of the hybrid system. Additionally, different parameters including borehole total length and heat pump capacity are varied to evaluate their impact on the seasonal system performance. The results show that by adequate sizing, total and peak electricity consumption of theDX-GSHPsystem can be reduced by 50% and 40%, respectively, compared to an undersizedDX-GSHPsystem.However,systemenergysavings from using a hybrid ground-source heat pump (HGSHP) are marginal compared to a DX-GSHP (5.5% for a low-capacity system), and these savings are happening during the shoulder months. Such results highlight the importance of further investigations in the area of DX-GSHPs to reduce the borehole installation cost and increase its performance.