Techno-economic parametric analysis of large diameter shallow ground heat exchanger in California climates

A parametric study of a large diameter, shallow bore ground heat exchanger system coupled to a water-to-air heat pump is presented. The performance of this system is compared to an equivalent air-to-air heat pump system. Building loads from a single-family home in two different climate zones with different magnitudes and ratio of winter and heating loads are used in this study. In the first climate zone (Sacramento, CA), the winter load is two times the summer load while in the second climate zone (Riverside, CA), the winter and heating loads are nearly balanced. A validated capacitance–resistance numerical model (CaRM-HP) is used to model the heat transfer from the ground heat exchanger. System performance and installation costs are evaluated for varied parameters including borehole diameter of the helical coil, depth of helical coil, spacing, and configuration of the bore field. For all configurations considered, the ground-source heat pump system consumes less electricity annually than the air-source case. The GHE with 40.6 cm (16 in.) helix diameter, 6.09 m (20 ft) helix depth borehole, 1.27 cm (½ in.) nominal tubing diameter with bore backfilled with sand results in the lowest installed cost relative to saved energy for the analysed climate zones. For Sacramento, this configuration results in an installed cost $4.48/kWh saved per year and saved 28.3% of the electricity relative to the air-source system. For Riverside, this GHE design leads to an installed cost of $4.74/kWh saved per year and saved 28.5% of the electricity consumed by the air-source system. The installed cost of the He-GHE is compared against that of a photovoltaic array with and without battery storage on a time-dependent valuation energy basis.