Thermal interaction of multiple ground heat exchangers under different intermittent ratio and separation distance

Heat transfer of multiple vertical ground heat exchangers (GHEs), the key component of ground source heat pump (GSHP) systems, should be paid more attentions in the soil temperature response, thermal interaction among boreholes and the consequences of heat exchange capacity decline. In this paper, based on their relative location, boreholes are firstly classified as corner boreholes, center boreholes and side boreholes, and then the thermal interference coefficient is proposed to evaluate the thermal properties under various intermittent ratios and separation distances. The calculation model consider the difference of borehole wall temperature, which is accurate and needs short calculation time because of combination analytic solution and numerical simulation. The results show that the heat transfer performance of each borehole remains almost the same until thermal interference emerges, the order of heat transfer flux over time is corner borehole > side borehole > center borehole. Increasing either the intermittent ratio or the separation distance can enhance the heat transfer over the same running time. The thermal interference coefficient increases with continued operation, increasing both the intermittent ratio and the separation distance can decrease the overall soil temperature, thus decreasing thermal interference. The coefficient can be reduced by nearly 1/3-1/2 under an intermittent mode compared with a continuous mode. (C) 2016 Elsevier Ltd. All rights reserved.