Study on the influence of borehole spacing considering groundwater flow and freezing factors on the annual performance of the ground source heat pump

Considering freezing and groundwater flow simultaneously, a three-dimensional finite element dynamic simulation platform of the ground source heat pump system (GSHPS) is established, and the GSHPS performance in an office building is analyzed by using this platform. The results show that the GSHPS performance can be improved by increasing the borehole spacing and considering freezing and groundwater flow together. Compared with the borehole spacing of 3.5 m, the average coefficient of performance (COP) of the unit increases by 2.2% in cooling period and 15.4% in heating period when the borehole spacing is 5.5 m. Compared with considering both freezing and groundwater flow, the average COP of the unit without considering freezing and groundwater flow, considering only freezing and considering only groundwater flow decreases by 11.9%, 9.3% and 4.2% respectively during heating period in Harbin. The influence of considering both freezing and groundwater flow on the GSHPS performance decreases with the decrease of load ratio (accumulated heating load divided by accumulated cooling load). The order of soil freezing penetration distance in different areas is: unsaturated area > downstream area > vertical area > upstream area, and that around different boreholes is: central borehole > boundary center borehole > boundary intersection borehole.

Automated summary

The study demonstrates that increasing borehole spacing and considering freezing and groundwater flow simultaneously can enhance the performance of ground source heat pump systems. There are significant differences in soil freezing penetration distance in different areas and around different boreholes.