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The design phase of ground source heat pump systems is an extremely important one as many of the decisions made at that time can affect the system's energy performance as well as installation and operating costs. The current study examined the interpretation of thermal response testing measurements used to evaluate the equivalent ground thermal conductivity and thus to design the system. All the measurements were taken at the same geological site located in Molinella, Bologna (Italy) where a variety of borehole heat exchangers (BHEs) had been installed and investigated within the project Cheap-GSHPs (Cheap and efficient application of reliable Ground Source Heat exchangers and Pumps) of the European Union's Horizon 2020 research and innovation program. The measurements were initially analyzed in accordance with the common interpretation based on the first-order approximation of the solution for the infinite line source model and then by utilizing the complete solutions of both the infinite line and cylinder source models. An inverse numerical approach based on a detailed model that considers the current geometry of the BHE and the axial heat transfer as well as the effect of weather on the ground surface was also used. Study findings revealed that the best result was generally obtained using the inverse numerical interpretation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a numerical model to analyze the thermal behaviour of vertical ground heat exchangers with a helical shaped pipe is presented. This type of configuration can be a suitable alternative to conventional ground heat exchangers, especially when the heating and cooling loads of the building are very low. The model describes the heat transfer problem by means of a network of interconnected thermal resistances and capacitances. Moreover, as the investigated ground heat exchanger is usually installed in shallow depth, the model takes into account the interaction between the ground and the ambient environment which affects the fluid heat carrier temperature into the heat exchanger and, as a consequence, the energy efficiency of the heat pump. After a sensitivity analysis on the mesh parameters, the presented model is compared with experimental data and the simulation results show good agreement with the measurements. Finally, analyses to investigate the influence of the weather conditions, of the axial heat transfer and of the pitch between the turns of the helical pipe for two types of ground are carried out. [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]

Highlights: [•] Ground source heat pump in geothermal basins is investigated. [•] TRT has been done to describe the ground properties. [•] Improvement of the heat pump performance is found. [•] GHE directly coupled with building is the best case in term of primary energy need. [Copyright &y& Elsevier]