Geothermal heat exchange in boreholes with independent sources

Geothermal boreholes have been used for many years to extract and store thermal energy. For a long time, the behavior of such systems was studied using analytical and numerical models, but the configurations were mostly limited to one inlet and one outlet per bore field. In recent years, some interest has been given to more complex bore field systems, in which heat can be shared between suppliers and customers. This paper is concerned with a system that shares energy through two independent loops within the same borehole. In the literature, a model was recently found to study the heat transfer in this type of arrangement, but it is limited to a symmetric configuration. This paper broadens the method to non symmetric borehole configurations. A comparison is made between the performance of an optimum configuration and a symmetric one. In one application, with two heat pumps, one in cooling mode and one in heating mode, as much as 3.5% improvement was observed between both configurations. However, in our second application, where a detailed hourly simulation coupling residential heat pumps and solar collectors to the same bore field is presented, the non-symmetric configuration energy consumption of the heat pumps gave comparable results to the symmetric configuration. Further analysis would be needed to evaluate the full impact of all the parameters on the final performance of independent loops. (C) 2015 Published by Elsevier Ltd.