Thermal Interference Between Neighbouring Ground-Source Heat Pumps : Tools to Calcualte it and Solutions to Limit it

Sammanfattning: Ground Source Heat Pumps (GSHPs) have emerged as a promising technology for decarbonization of the heating sector. However, their increasing prevalence in densely populated areas may lead to considerable changes in the ground temperature, which can ultimately lead to reduced performance of the systems. Being able to forecast the ground temperature change in areas with a high density of GSHPs is therefore important for a correct management of the geothermal resource and the proper design of the systems. The main scope of this thesis is to propose a new heat transfer model that enable the calculation of the ground temperature development in areas with several GSHP systems connected to vertical borehole heat exchangers. This work resulted in two new models, here referred to as FLSIV and FLSIVTBC, which are built upon the Finite Line Source model, a classic building block for semi-analytical models dedicated to geothermal boreholes. The application of these models to realistic scenarios representative for Stockholm has revealed a potentially significant interference between neighboring geothermal boreholes in densely populated areas. Therefore, a secondary objective of this thesis is to explore possible strategies for limiting this interference. The last section of this thesis investigates the possibility of increasing the borehole length or reducing the thermal load to constrain the ground temperature change, and the possibility of limiting the number of GSHPs in an area to prevent a severe drop of system performance. The results showed that the first two strategies may require a significant change in the operation or design of the systems, while the third strategy may permit a high utilization of GSHPs without modifications of the systems. Keywords: Ground source heat pumps, Thermal interference, Neighboring geothermal borehole, Finite Line Source, Mitigation strategies.