The observed effects of changes in groundwater flow on a borehole heat exchanger of a large scale ground coupled heat pump system

A study was completed comparing the effectiveness of a borehole heat exchanger (BHE) within a large scale closed-loop geothermal system to changes in groundwater flow, as a result of periodic pumping of a large municipal well. The BHE studied consists of 144 geoexchange boreholes drilled to a depth of 122 m into karstic bedrock of the Ozark Aquifer. Estimated groundwater flows rates range from 15 to 1.1 × 10−3 m/year were measured, and the effectiveness of the BHE during pumping was calculated to understand the effects of groundwater flow on the system. Changes in the BHE effectiveness under varying flow rates were compared to estimates from previous study estimates with changes in aquifer saturation. Overall, the variations in aquifer saturation tended to have the greatest influence on the effectiveness of the BHE.