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Ground-coupled heat pumps are increasingly being utilized to heat and cool buildings. Although it is difficult to size and to predict their behavior and performance, their design can be optimized via simulations. EnergyPlus is a popular energy simulation program for modeling building heating and other energy flows and, since it is organized to consider borehole heat exchangers via the well-known g-functions approach, it can be used advantageously for that purpose. The Capacity Resistance Model is another recent numerical simulation tool devoted to ground and borehole heat exchangers. In this work, two methods to calculate the g-fucntions were analyzed, using as case-study a real office building, whose imbalance between the heat extracted and injected into the ground was found to be appreciable. The energy imbalance involves a ground temperature drift affecting the system efficiency. The results of the EnergyPlus g-functions and the Capacity Resistance Model model approaches were compared. The capacity of the two methodologies to accurately simulate this phenomenon were analysed also with reference to the available building's long-term monitoring data. The analysis showed the importance of using g-functions suitable to reflect the layout of the borehole field, in order to correctly evaluate the energy performance of the entire ground source heat pump system. [ABSTRACT FROM AUTHOR]

Energy foundation piles can be an efficient cost-effective solution for ground source heat pump applications. As they are very different from standard ground heat exchangers, numerical or analytical models usually used to investigate their thermal performance must be carefully analysed before they can be applied. The total length of ground heat exchangers is a critically important factor in the overall design of a ground source heat pump. Ground thermal properties are the primary parameters affecting the size of ground heat exchangers. The thermal response test is the most commonly used procedure to determine the ground’s thermal conductivity. The current study investigated a thermal response test on a 20 m long energy foundation pile equipped with a double U-tube circuit. The test measurements were interpreted using both the infinite line source model and inverse numerical analysis by means of a detailed model that was able to consider both the actual geometry of the pile and the axial heat transfer. The results indicated an approximately 50% difference between the two values of ground thermal conductivity. The effect of this evaluation on the calculation of the energy piles’ total length was first investigated utilizing a method outlined in the literature. The consequences on the long term energy performance of a ground source heat pump system were then investigated using numerical simulations and taking into consideration the effect of the spacing between the foundation piles. It was found that the total length calculated using the result based on the infinite line source model was about 20% lower than that obtained using the inverse numerical approach. An approximately 10% difference in the heat pump’s seasonal energy efficiency was also found. [ABSTRACT FROM AUTHOR]

Abstract: There is a rising interest in heating and cooling systems based on renewable energy sources. Air heating or cooling with earth-to-air heat exchangers (EAHE) is one approach for reducing ventilation heat losses and improving thermal comfort in buildings. A literature research was performed in order to analyze the design, characteristics of earth-to-air heat exchangers and whether they could be coupled with HVAC system coupling. A range of projects was compared in order to collect and summarize design suggestions. [Copyright &y& Elsevier]

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]