Estimation of ground thermal conductivity by inverse heat transfer method using temperature measurements from a U-tube boreholes heat exchanger

The ground heat exchanger (GHE), as a critical component of a ground source heat pump (GSHP) system, can be utilized for heating and cooling the buildings as well as increasing the energy efficiency in domestic applications. The thermal conductivity of the ground is a key design parameter for GSHP systems. This study estimates the ground thermal conductivity for a U-shaped ground heat exchanger through the inverse heat transfer method. In this process, to solve the direct problem of the U-tube boreholes heat exchanger, a three-dimensional transient computational fluid dynamics solver is developed. The current parameter estimation problem was solved using two distinct series of sensor temperatures. One series is the borehole wall temperature at a depth of 0.5 m. The other is the inlet and outlet water temperature of the geothermal heat exchanger. The duration of the simulated experiments was considered to be 5 hours. The parameter estimation results show that using the wall borehole temperature results in a more accurate estimation of ground thermal conductivity than the inlet and outlet temperature of the heat exchanger. This is because the wall temperature is more sensitive to change in ground thermal conductivity than inlet and outlet water temperature. It was also shown that the estimation error decreases by decreasing the inverse method time step.