Feasibility Study of a Residential Hybrid Ground Source Heat Pump System

Abstract

A residential hybrid ground source heat pump (HGSHP) model is presented, which integrates a compact cooling tower with a GSHP. The base case GSHP model is for a single story, 195 m2 house with a 14 kW heat pump and four 68.8 m deep vertical boreholes and uses Austin, TX weather data. The GSHP model was run for a range of supplemental heat rejection (SHR) capacities of an unidentified device located between the heat pump outlet and ground loop inlet, and estimates of improved heat pump performance and ground temperature effects are presented. Then, a compact closed wet cooling tower (CWCT) model is presented and coupled to the GSHP model. The tower's 7 kW capacity represents the smallest commercially available cooling tower. Each of the four HGSHP boreholes was reduced to 26.5 m. The operational and economic performance of the HGSHP is compared to a GSHP alone. Metrics include estimates of initial and lifetime operational costs, ground temperature effects, and heat pump efficiency. Simulations for ten years of operation show that adding the compact CWCT is cost effective, extends the lifetime of the borehole system, and maintains high heat pump efficiencies.