Changes in the ground surface temperature, as it can occur in built-up areas or due to climate change, affect the temperatures of geothermal boreholes. Analytical models for the thermal simulation of boreholes and consid-ering this factor have been proposed. However, they all impose a uniform heat extraction boundary condition along the borehole walls. This boundary condition overestimates the temperature change in the underground caused by the borehole heat extraction and underestimates it in case of rejection. More accurate results are most often obtained by imposing a uniform temperature boundary condition.In this paper, we propose a new model to calculate the boreholes wall temperature taking into account both the heat extractions/rejections from all the boreholes in the area and the change in ground surface temperature. The model is tailored for areas with independent ground source heat pumps and imposes a uniform temperature boundary condition along the borehole walls, overcoming the limitation of the existing models.We apply the new model to a real Swedish neighbourhood and show that existing systems may already be significantly affected by the increased ground surface temperature due to urbanization. We also compare our new model with an existing similar model and show that while the two models provide similar results for smaller areas, their difference tends to be relevant for bigger areas - including the real Swedish neighbourhood analysed -thus making the application of our model important for neighbourhood-and city-scale studies.

Ground Source Heat Pumps (GSHPs) connected to Borehole Heat Exchangers (BHEs) are a fast-growing technology for thermally efficient buildings. Therefore, areas with several independent GSHP installations close to each other are becoming more and more common. To guarantee an optimal operation of these systems, it is necessary to design them considering the influence of the neighbouring installations. However, a tailored model for this scope has not been found in the literature. In this paper, we aim at filling this gap by proposing and validating a methodology to calculate the thermal influence between neighbouring independent boreholes. It is based on the Finite Line Source (FLS) model and prescribes novel boundary conditions, tailored to hydraulically independent boreholes. The methodology allows to prescribe different thermal loads to different BHEs and imposes uniform temperature boundary condition on each borehole wall. We also show how to implement and apply the model. Our application shows a thermal influence of up to 1.5 K during the lifetime of a GSHP and of up to 0.8 K during the first year of operation in an area with a relatively low number of installations, underlying the importance of considering the thermal influence and the usefulness of our proposed model. Finally, a sensitivity study on the ground thermal conductivity shows the importance of a correct estimation of this property for accurate simulation results.

Ground source heat pumps (GSHPs) are a state-of-the-art technology for heating, cooling, and hot water production. They are already common in several countries and represent a promising technology for others. As the technology penetrates the market, the number of ground heat exchangers in densely populated areas may increase significantly. Therefore, it becomes important to consider the thermal influence of neighboring GSHPs while designing these systems in such areas. This question has become more frequent in some Swedish residential areas where the use of GSHPs is very common. This article proposes an easy-to-implement methodology to evaluate the thermal influence between borehole heat exchangers (BHEs) in areas with a high number of GSHPs installed. It also suggests two mitigation strategies to decrease the thermal interference so that the given limit for the ground temperature change is respected. The methodologies proposed are implemented using the programming language Julia and applied to fictional scenarios relevant for Sweden. It is found that neglecting the presence of neighboring systems might lead to an overexploitation of the underground heat. This can be avoided if, during the design phase, the presence of neighboring BHEs is taken into account and mitigation strategies are applied.