Energy efficiency characteristics of U-tube ground heat exchangers under non-influent conditions

Selecting infinite distance boundary, simulates the heat transfer process of the ground heat exchangers(GHE) under non-influent conditions by using three-dimensional numerical model. Investigates the major impacting factors of energy efficiency coefficient of GHE. The results show that increasing soil-rock heat transfer capability and buried depth and properly decreasing flow rate inside the GHE can improve the energy efficiency coefficient, but enlarging the distance between two legs can take effect on the energy efficiency of heat transfer in a short run time, that adopting intermittent operation mode with shorter periodic cycles and longer temperature recovery time is helpful for increasing the energy efficiency coefficient of GHE, and that the initial temperature of soil-rock body and inlet temperature of GHE have no effect on the energy efficiency coefficient.