Analytical solution for multi-borehole heat exchangers field including discontinuous and heterogeneous heat loads

peer reviewedClosed-loop borehole heat exchangers (BHEs) are used for heating/cooling buildings. For the sustainable design of these systems, analytical solutions provide fast and flexible tools to investigate the subsurface thermal response. In this study, from an existing analytical solution which predicts temperature field for discontinuous heat extraction/injection of multi-BHEs field, is improved to consider the case of heterogeneous heat loads (HHLs), i.e. heat loads tuned independently for each BHE to improve the long-term heat refurbishment in the subsurface. Also, we implemented the concept of BHE thermal resistance in order to determine the heat carrier fluid temperature. To provide accurate extreme temperatures, two aspects were analysed: the time step discretization; and the temporal resolution of thermal loads. The requirement for defining hourly thermal loads was demonstrated in order to properly predict extreme temperatures in the subsurface, as would be the case in an optimization problem of multi-BHEs with HHLs. As a study case, we showed the interest of HHLs to reduce localized thermal exhaustion of the geothermal system and to reduce extreme temperature variations and thermal drift in the most critical BHEs