Experimental and numerical analysis on thermal performance of large-diameter cast-in-place energy pile constructed in soft ground

An energy pile equipped with a W-type heat exchange pipe was constructed in reclaimed soft ground, which is fabricated in a large-diameter cast-in-place pile. The diameter of the energy pile is 1.5 m and the drilled depth reaches to a 60 m whilst the heat exchange pipe is inserted to 30 m depth from the ground surface. To evaluate thermal performance of the constructed energy pile, a series of in-situ thermal performance tests was carried out by controlling intermittent cooling and heating loads, in which the inlet and outlet fluid temperatures, flow rate, and temperatures inside the energy pile were recorded. The test results show that a large-diameter cast-in-place energy pile can provide sufficient heat exchange compared with other types of ground heat exchangers. A series of CFD analyses was performed to simulate the thermal performance tests and provide the designer with preliminary estimation of thermal performance of energy piles. The numerical model was verified by comparing with the field measurements. Using the developed numerical model, the thermal behavior of the energy piles was evaluated with various parameters, and effects of the thermal interference and the temperature difference between the fluid and ground formation on the thermal performance were discussed.