Influence of loop type, pipe diameter and soil temperature on performance of ground heat exchangers

Establishes a three-dimensional mathematic model for single U-and double U-type ground heat exchangers, and researches the heat transfer performance of the two type ground heat exchangers with the pipe diameter of 25 mm and 32 mm. The results show that the heat exchange of the double U-type ground heat exchanger increases by 20% than that of the single U-type ground heat exchanger with the same pipe diameter, but the single U-type ground heat exchanger of 25 mm diameter will achieve larger water temperature difference between inlet and outlet; for the double U-shaped ground heat exchanger of 32 mm and 25 mm diameter, the former has not more significant advantage than the latter; for an actual project, if the area of land to be occupied is sufficient, the single U-type ground heat exchanger of 25 mm diameter is preferable, otherwise the double U-type ground heat exchanger of 25 mm diameter should be selected; when the soil temperature increases by 1 ℃, the outlet water temperature increases by 0.23 ℃, and the heat exchange decreases by 5%.