Studies on the performance of ground source heat pump affected by soil freezing under groundwater seepage

Groundwater seepage and soil freezing will affect heat transfer ability in soil and the operation performance of ground source heat pump system (GSHPS) in cold regions during heating period. In this paper, a full-scale dynamic simulation platform for the ground heat exchangers (GHEs) performance under typical geological conditions is established, and the soil freezing characteristics and dynamic performance of a GSHPS at different seepage velocities are studied. This realizes the real-time coupling between the temperatures at the inlet and outlet of the buried pipes and the building loads, which is more suitable for actual operation of GSHPS. The results show that with the increase of seepage velocity, the soil freeze later and thaw earlier, and the freezing shape and size of the area around the borehole will also change. When seepage velocity is 0, 0.1, 0.5 and 1.0 m/d, the outlet temperature of GHEs with soil freezing factor is higher than that without freezing and the maximum difference between them is 2.68, 2.41, 1.40 and 0.95 K, and the minimum heating coefficient of performance (COP) with freezing or not are 2.24/2.00, 2.43/2.22, 2.82/2.74 and 3.04/2.99, respectively. Therefore, whether soil freezing is taken into account or not, the difference is getting smaller, and the influence of soil freezing on system performance weakens gradually with seepage velocity increasing. The influence of groundwater seepage and soil freezing on soil temperature field and system performance are quantified, which provide a reference for the design and operation of GSHPS.