Numerical study on efficiency and applicability of prefabricated modular ground heat exchangers in shallow depth

Abstract

This study developed and validated a CFD model to evaluate the performance of modular ground heat exchangers (GHEs) compared to vertical closed-loop GHEs. The reliability of the model was confirmed through comparison with field experiment data, with RMSE values of 0.35 °C and 0.27 °C for inlet and outlet temperatures, respectively. Additionally, the performance of modular GHEs installed at shallow depths was evaluated under various external environmental conditions, revealing a temperature difference of approximately 7 °C between the intermediate and cooling periods. A comparison of the performance of modular and vertical GHEs of the same heat exchanger length showed that, when a constant heat load of 2 kW was maintained for 100 h, the temperature in the vertical GHE increased to 32.8 °C, while the modular GHE reached 38.5 °C. Despite the high thermal conductivity resulting from ground heat storage effects, the modular GHE exhibited a greater temperature increase due to its shallow installation depth compared to the vertical GHE. On the other hand, as the thermal conductivity of the ground decreased, the temperature difference between the two systems also decreased. These results suggest that modular GHEs can be a cost-effective and efficient solution, particularly in regions with low ground thermal conductivity.