Study on heat transfer model of coaxial borehole ground heat exchangers

Heat transfer model is an important basis for the design and simulation of coaxial borehole heat exchangers, however, the existing heat transfer models of coaxial borehole heat exchangers have some disadvantages, such as low precision or too much computation time. A new heat transfer model of coaxial borehole heat exchangers is proposed, in which two-dimensional (radial and axial) heat transfer in the borehole is analysed by the thermal resistance and capacity model, and one-dimensional (radial) heat transfer outside the borehole is analysed by the infinite cylindrical-source model. The model is applied to a distributed thermal response test, and the simulation results are compared with the experimental data and the results of another model. The results show that the calculation results of the model match better with the experimental data, and that the short-time fluid temperature distribution and inlet and outlet fluid temperatures calculated by the model have high precision.