Heat transfer of ground heat exchanger for GSHP（3）：transient heat transfer characteristic of U-type ground heat exchanger with variable heat flow boundary

Studies the transient heat transfer characteristic with numerical calculation method and analytic solution. Divides the calculation area into two parts based on the boundary of borehole wall, the calculation method is steady analytic solution for the area in the borehole, and the finite volume method for the soil area. Obtains the variety patterns of outlet water temperature, transient borehole wall temperature, heat exchange capacity per length and temperature distribution in certain distances from the pipe. The result can be used as a reference for the dynamic simulation, optimum design and improvement of GSHP.