An improved infinite composite-medium cylindrical source model for single U-tube ground heat exchanger

Abstract

In this paper, a new heat transfer model for single U-tube ground heat exchanger is proposed. By considering the influence of U-tube heat capacity, an improved infinite composite-medium cylindrical source model is established to calculate the average fluid temperature, and then combined with a quasi-3D heat transfer model in borehole, the inlet and outlet fluid temperatures are derived as functions of average fluid temperature and the heat flow, therefore the inlet and outlet fluid temperatures of U-tube can be calculated. To verify the feasibility of the proposed model, it is applied to a sandbox experiment and compared to other models. The result shows that the inlet and outlet fluid temperatures calculated by the proposed model are accurate in the whole time period. Compared to other models, the inlet and outlet fluid temperatures calculated by the proposed model are in better agreement with the experimental data especially during short time, and the mean absolute percentage error, maximum absolute error, mean absolute error and root mean squared error are basically smaller. The mean absolute errors of the inlet and outlet fluid temperatures predicted are 0.11 ?C and 0.09 ?C, respectively, and the maximum absolute errors are less than 0.4 ?C.