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Abstract: Several models are available in literature to simulate ground heat exchangers. In this paper an approach based on electrical analogy is presented, for this reason named CaRM (CApacity Resistance Model). In some cases several information are needed during design: both the borehole and the surrounding ground are affected by thermal exchange. The model here presented allows to consider the fluid flow pattern along the classical vertical ground heat exchangers as a single U-tube, a double U-tube or coaxial pipes. Besides, ground temperature at different distances from borehole are calculated, taking into account also the thermal interference between more boreholes. Starting from the supply temperature to the heat exchanger, the outlet fluid temperature is calculated and the ground temperature in each node, step by step. The model has been validated by means of a commercial software based on the finite differences method. Further comparisons have been carried out against data from a ground thermal response test and from the survey of an office building equipped with a ground coupled heat pump and vertical double U-tube heat exchangers. The agreement of results validates the model here presented. [Copyright &y& Elsevier]

An important consideration with regard to ground source heat pump (GSHP) systems is ensuring high energy efficiency performance throughout the years. Multi-year analyses are thus exceedingly important to evaluate the seasonal oscillations in the ground temperature and its long-term drift. As only a limited number of results based on real cases are available in the literature, this work aims to address this paucity of information. Seasonal and long-term computer simulations were conducted in order to investigate the thermal performance of two office buildings in Italy with unbalanced load profiles. The study focuses on the evaluation of ground temperature drift which was essentially due to an imbalance of the buildings’ load profile. An analysis, which was compared to two analytical approaches available in the literature, was carried out using a detailed numerical model. The effects of improved load balancing of the ground load profile and of a higher number of boreholes on seasonal oscillations and on the thermal drift were investigated. The results showed that rebalancing the ratio between the heat extracted from and injected into the ground led to better results from an energetic viewpoint almost certainly synonymous with an energetic-economic optimization. [ABSTRACT FROM AUTHOR]