Research On The Soil Temperature Around Borehole Of Ground Source Heat Pump Noncontinuous Operation

Ground Source Heat Pump used in the subtropical region in China, due to the building's cooling load in summer is bigger than heating load in winter, it is prone to accumulate underground heat, so with the running time increases, the soil temperature around borehole also increases slowly. In this paper, mainly discuss the problem of imbalance of the acquisition and release of underground heat. Analysis of the object aims at the heat transfer principle and trend of the soil around the drilling hole of U-tube heat exchanger, it is mainly based on the noncontinuous operation strategy.Through the analysis of unsteady heat transfer of ground source heat pump and the characteristics of noncontinuous operation strategy, by using the finite source term model and superposition principle which is suprior than the traditional unlimited long-term heat source model, established heat transfer model both in the vertical and horizontal direction. Based on MATLAB mathematical software, the program can simulate different soil under the thermal physical parameters, at any time, any radius and depths of soil temperature field.According to the characteristics of the finite source term model, the experimental platform height is simplified to 1.5 meters high. By the experiment analysis of soil temperature field in summer working condition of continuous operation and intermittent operation, in the middle of the experimental platform height(0.75m), the relative measuring errors are 20% of the projects within the permitted, it well validated the accuracy of this finite source term model, it is reasonable to use this depth temperature in a certain radius as the representative temperature.By some appropriate modification of the MATLAB program, the soil temperature field around the drilling hole of several noncontinuous operation strategies are simulated and analyzed, the intermittent operation and alternate operation can effectively solve the problem of imbalance of the acquisition and release of underground heat, it can also significantly reduce the single well thermal effect radius.Meanwhile, for the influence of different heat input and soil coefficient of thermal conductivity, the paper also made qualitative and quantitative analysis. The results showed that the ground source heat pump non-continuous operation is very effective to improve the problem of the heat imbalance of soil temperature around borehole,and it is helpful for guiding engineering application of the ground source heat pump.