Strategic optimization of borehole heat exchanger field for seasonal geothermal heating and cooling

Abstract

A mathematical procedure for optimization of borehole heat exchanger (BHE) fields is presented. If heat extraction and injection is not seasonally balanced, thermal anomalies grow in the ground. These are commonly constrained by regulations and not desirable due to potential decline of the system’s performance. We demonstrate, for the case with heat extraction and only partial replenishment, how adjustment of seasonal heating and cooling workloads can mitigate local cooling of the ground. It is revealed that the benefit from mathematical optimization increases with heat extraction/injection imbalance. Evidently, strategic operation of individual BHEs in the field can to some extent compensate for the heat injection deficit. Additionally to the optimization of workloads, we inspect the required number of BHEs for a given heating/cooling demand. The idea is that by sequentially removing least effective BHEs in the field, investment cost are reduced, while the effect on the entire field performance is minimal. We show that such unfavorable BHEs exist mainly in non-optimized fields without replenishment. Thus, our work offer two ways of tuning BHE fields applied for geothermal heating and cooling: workload optimization of individual BHEs and removal of redundant BHEs for a given arrangement.