From ground source heat pump monitoring to modelling of temperature field around borehole heat exchangers
Closed-loop and vertical Borehole Heat Exchangers (BHEs) are a common solution adopted for shallow geothermal energy systems. However, during the operational life of such systems, the evolution of subsurface temperatures is rarely monitored. As a result, Ground Source Heat Pump (GSHP) settings are typically adjusted solely based on the building’s heating and cooling demands, without considering the thermal state of the ground. This can lead to either depletion of the ground heat reservoir and reduced system performance over seasonal cycles or under-exploitation of available thermal resources, representing a missed opportunity in terms of return on investment. This study demonstrates how long-term monitoring of a residential GSHP installation can be used to assess the performance of the system, to identify operational patterns, and to evaluate the sustainability of its interaction with the subsurface. Four years of inlet and outlet fluid temperatures, flow rates, and electricity consumptions were collected at the GSHP of a Belgian single-family house equipped with one 107 m deep BHE. These data were processed to distinguish operating modes, analyze the seasonal evolution of the borehole fluid temperature, quantify extracted and injected heat according to the operating modes, and compute performance indicators. In addition to the monitoring analysis, a preliminary modelling exercise was carried out using an existing analytical heat transfer model for BHEs based on g-functions for finite line source model. The monitored heat load extracted or injected in the ground was used as input, and simulated fluid temperatures were compared with measurements to explore the potential of such modelling for future calibration and predictive applications. While not intended as a fully validated predictive tool in this study, this first comparison illustrates how combining monitoring data with heat transfer models could ultimately support more informed and sustainable operational strategies.