Effects of Ground Loop Design Parameters on Short- and Long-Term Operational and Economics of Ground Source Heat Pumps in Hot, Semi-Arid Areas

Deployment of ground source heat pumps in Texas and the Southwest has been limited by high initial cost and potential ground heating. To address these limitations for a residential application a sensitivity study of the ground loop design parameters was completed. The study uses an integrated building load-ground source heat pump model that is designed to be a test bed for assessing the short- and long-term performance of GSHPs. This study examines a 195 m² residential house located in Austin, Texas with a 14.6 kW heat pump and 4 vertical boreholes each with a length of 68.5 m. The performance effects and the long-term economics of the total ground loop length, spacing of the boreholes, placement of the boreholes, grout thermal conductivity, and supplemental heat rejector sizes are compared. The study shows the importance of proper sizing, design, and placement of the borehole in locations with severely unbalanced heating and cooling loads.