Numerical study on the ground temperature field around large-area compact U-shaped pile-buried heat exchangers.

The imbalance between heat injection and extraction from and to the ground has been a prime focus in most ground source heat pump (GSHP) applications. Based on the calculation of the hourly cooling and heating loads of buildings, numerical simulation of the heat-transfer behaviour of the ground surrounding large-area compact U-shaped pile-buried heat exchangers has been carried out. The concept of heat barrier (HB) during heat transfer has been presented and further characteristics including random movement, dynamic shape and potential harmfulness have been analyzed. During the long-term operation of GSHP system, the growth rate of HB temperature is higher than that of average ground temperature, which may lead to the soil's peak temperature and sometimes affect short-term operation of heat pump units. Both energy equilibrium and HB analysis should be taken into account in order to guarantee the stability and reliability of GSHP systems.