Long-Term Thermal Performance Monitoring for Large-Diameter Cast-In-Place Concrete Energy Pile

The energy pile constructed in a reclaimed land is a large-diameter drilled shaft equipped with two different types of heat exchange pipe configurations, i.e., a W-shape and S-shape, respectively. The diameter of energy pile is 1.5m and the drilled shaft reaches to a depth of 60 m whilst the heat exchange pipes are installed to about 30 m depth from the ground surface. To evaluate its thermal performance, a series of long-term monitoring has been performed by controlling intermittent heating modes with the aid of a constant-temperature water bath that enables the inlet fluid temperature to be maintained as 5°C. In the course of the experimental measurement, the inlet and outlet fluid temperatures, pumping rate, and temperature inside the energy pile were continuously recorded. The monitoring result shows that a large-diameter cast-in-place concrete energy pile was operated with stable and efficient heat exchange rate comparing with other energy pile systems. In addition, a series of CFD numerical analyses were performed to simulate the long-term thermal performance of the large-diameter cast-in-place concrete energy pile and to provide system designers with preliminary estimation of the thermal performance of energy piles.