Thermal response tests (TRT) are used to investigate the thermal properties of the ground for dimensioning borehole heat exchangers. This study analyzes the versatility and limitations of TRT in energy piles. Several analytical solutions are presented for the temperature response of the borehole system with a finite element model (FEM) used to study the effect of convection for different pile diameters, different types of pipes and different heating powers. The results show that the TRT tests can be used in energy piles but the minimum duration of the tests increases with increasing pile diameter, while the types of pipes and the heating power have no effects. The accuracy of the FEM model was verified by simulations of Beijing TRT tests on CFG (cement fly-ash gravel) piles with the results indicating that the high heating power is not appropriate. TRT tests may take hundreds of hours for large diameter piles (larger than 400 mm); thus, lab tests for the thermal parameters are suggested using undisturbed borehole samples.
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