Restoration performance of vertical ground heat exchanger with various intermittent ratios

• The effect of intermittent operation restoration performance was investigated.
• A new heat transfer model of ground heat exchanger is proposed.
• The intermittent ratio of best restoration performance is 3.

Based on five intermittent operation modes with the intermittent ratios of 0.7, 1, 1.4, 2 and 3, the effect of intermittent operation on restoration performance of vertical ground heat exchanger in Ground Source Heat Pump was investigated in terms of heat exchange flux, temperature difference, soil temperature distribution and thermal radius. Meanwhile, a heat transfer model of the GHE has been developed by combining the analytical solution and numerical solution, whose calculation area has been divided into two parts by the boundary of the borehole wall. For the area in the borehole, the calculation method is steady analytical solution based on energy conservation, whereas for the soil area, the finite volume method is adopted, and the two parts are coupled by the temperature and heat flux of the borehole. The simulation results indicate that intermittence operation modes can improve the heat exchange performance of ground heat exchanger. Furthermore, when the intermittent ratio is 3, the restoration performance is the best due to the longest stopping time. With the operation proceeding, the enhancement of the heat flux arising from the intermittence becomes more obvious while the restoration ratio of average temperature of borehole decreases simultaneously.