Study on the heat transfer performance of deep-buried pipe energy piles with different pile length-to-depth ratios

To achieve the “dual carbon” goals, this paper proposes a new structure, the deep-buried pipe energy pile, to overcome the limitations of heat exchange efficiency associated with traditional energy piles. Using a combination of model tests and numerical simulations, a multi-field coupled thermal model of deep-buried pipe energy piles (pile-soil-pipe) is constructed. The heat transfer performance of the system under different pile length-to-depth ratios (L/D, where L is the pile length, D is the depth of the buried extension of the lower part) of deep-buried pipe energy piles is explored. The model test results indicate that under summer conditions, compared to ordinary piles, the average heat exchange of deep buried pipe energy piles increases from 585 to 765W – an increase of 30.8%, demonstrating superior heat exchange capability. The simulation results show that for a pile length of 10 m, for deep buried pipe energy piles with medium and small diameters (200 mm, 300 mm), when L/D reaches 10:3, the heat exchange amount increases by more than 30% compared to energy piles with the same diameter. In addition, the new structure lowers the center of the heat source, utilizing the heat storage potential of the deep stable temperature zone, which in turn enhances its heat exchange efficiency.