Optimized borehole spacing for enhanced ground source heat pump performance

The use of shallow geothermal systems for building climatization has expanded rapidly in response to decarbonization strategies and advances in heat–pump technology. However, Ground Source or Water Heat Pump (GSHP or GWHP) systems require specialized design expertise, and inadequate sizing may reduce efficiency while inducing subsurface thermal disturbances. These challenges are critical for closed–loop systems, where heat exchange is limited to the borehole heat exchanger (BHE), typically installed within aquifers. In borefields composed of multiple BHEs, predicting the spatial development of thermal plumes is essential to prevent thermal interference between BHEs and ensure stable long–term performance. Despite its importance, the literature provides only general recommendations regarding optimal lateral spacing between BHEs. This study addresses this gap by developing a practical methodology for determining suitable spacing in linear borefields oriented perpendicular to groundwater flow. The approach relies on numerical simulations using MODFLOW–USG, with BHEs represented through the Connected Linear Network (CLN) package to model coupled groundwater flow and heat transport. Simulations were performed by imposing fixed inlet temperatures within the U–tube and an undisturbed aquifer temperature, while systematically varying groundwater velocity, BHE length, and operational duration. This enabled quantification of both longitudinal and lateral extent of the thermal perturbation generated by the BHE. Based on these results, a technical abacus was developed to recommend optimal BHE spacing (1–7 m) as a function of hydrogeological and operational parameters. The tool provides practitioners with a rapid and reliable means of minimizing thermal interference and improving GSHP efficiency without requiring site–specific numerical modeling.