Zoning operation of multiple borehole ground heat exchangers to alleviate the ground thermal accumulation caused by unbalanced seasonal loads

When the heat extraction and injection of a borehole ground heat exchanger (GHE) are not seasonally balanced, ground thermal accumulation will occur and will cause a decline in the ground source heat pump's operational efficiency, especially for large multiple borehole ground heat exchangers (LMBGHE). A zoning operation strategy, in which only the relatively central part of the GHE runs during the low load season, is adopted in this paper to alleviate the thermal accumulation. By analyzing the case in which the heat injected into the ground in the summer is greater than that extracted from the ground in the winter, it was found that, in comparison with the full operation mode, the highest and average field temperatures significantly decrease when only the central part of the GHE runs during the winter. Analysis shows that the thermal accumulation can be effectively alleviated by this GHE zoning operation. This study also indicates that the zoning operation method is more effective when the ground has a smaller thermal conductivity. (C) 2015 Elsevier B.V. All rights reserved.