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.

Air-source heat pumps (ASHPs) and ground-source heat pumps (GSHPs) are the most spread heat pumps nowadays. However, they suffer from drawbacks that could be mostly overcome coupling the two heat sources, i.e., using dual-source heat pumps (DSHPs). In this study, we compared the techno-economic performance of ASHPs and GSHPs for a small Swedish single-family house. We also calculated the performance improvements achieved using dual-source heat pumps, and evaluated the economic conditions necessary to make the dual-source heat pumps economically competitive with the more traditional systems. We found that the GSHPs were more efficient than the ASHP during the first year of installation, but their performance decreased-sometimes dramatically-during their lifetime. However, investing in either systems was always beneficial and no significant differences tended to exist between the investments. The dual-source heat pumps had-sometimes significantly-higher performance than the conventional systems but they might not be economically competitive with the more conventional systems.

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) connected to vertical boreholes are popular systems to provide heat and/or refrigeration in residential and commercial buildings. The diffusion of these systems poses the question on how to effectively and sustainably handle the underground thermal resource without overexploiting it. In particular, this question can rise in densely populated areas where either heat extraction or heat rejection is dominant.Although several models are available and used to estimate the thermal influence between individual boreholes or group of hydraulically connected boreholes, the development of models that can quantify the thermal influence of neighbouring boreholes having different boundary conditions (it is the case for individual GSHP installations located in the same neighbourhood) is still at its early stages. The availability of such tools is essential both to enable the legislators to set appropriate rules for the allocation of the underground thermal resource and to enable the designers to properly size these systems.In this paper, we develop a model based on the stacked finite line source method that is tailored to estimate the thermal interaction of neighbouring GSHPs. The model takes as input the heat load of each GSHP and imposes uniform temperature on every borehole. The model is applied to a fictitious densely populated area to calculate the temperature changes on the boreholes walls of the systems. The results are compared with the results obtained with another model previously proposed by the authors.

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.

The residential sector accounts for a relevant share of global energy use; therefore it is important to use as much renewable energy as possible to satisfy its demand. Geothermal energy, among others, is nowadays used for this scope: more and more buildings in several countries are exploiting the underground to satisfy domestic heating, cooling and hot water demand by means of ground-source heat pumps. On the long run heat extraction/injection can lead to depletion of the ground as heat source/sink. Current tools only allow a designer to take into account the depletion of the ground caused by the system she or he is designing. However, the actual total heat depletion is also influenced by the surrounding systems. With the growing diffusion of ground-source heat pumps the ability of estimating the total underground heat depletion is of paramount importance. The aim of the article is to give an insight of the problem: the goal is to show what will happen in the underground if residential ground source heat pump systems are designed without taking into account the presence of neighbouring installations. The study is performed for different types of soil and borehole heat exchangers designs.

In densely populated areas where many ground source heat pump (GSHP) systems are present, it becomes important to consider the thermal influence ofneighbouring GSHP installations while designing these systems. This question has started to become frequent in cities like Stockholm in Sweden. For thedesign and performance analyses of the GSHP systems, simulations at different detail levels regarding time step are used. Borehole heat loads of realinstallations can be estimated with different time resolution from case to case. This article presents a first step towards the development of a model to calculatethe mutual influence of neighbouring GSHP installations: a first elementary model is developed to quantify such influence, then the error introduced whenperforming simulations with different heat load steps, i.e. annual and hourly, is analyzed from a perspective of multiple neighbouring GSHP installations.It is found that a negligible error is derived when considering low temporal resolution data.