Geometric arrangement and operation mode adjustment in low-enthalpy geothermal borehole fields for heating

The efficient operation of ground source heat pump (GSHP) systems with multiple borehole heat exchangers (BHEs) over a lifetime of decades implies an optimized performance of the BHEs and a mitigation of the environmental impact of the system. This paper introduces a new combined optimization approach, which adjusts the BHE positions as well as the individually regulated energy extraction for each single BHE within a given borehole field in conduction dominated media for a given seasonal changing load profile. The optimization of only the BHE positions without optimizing the individual BHE loads nearly produces the same improvement of the underground temperature change of approximately 12% as an optimization of the BHE loads without optimized positioning. The combination of both optimization approaches results in only slightly better results compared to a result achieved by only one of the optimization approaches. Thus for homogeneous fields without groundwater flow, an optimal load assignment can be substituted by an optimal BHE placement, which leads to a considerably reduced complexity of the borehole field.