Study on effects of multi-climatic parameters on performance of ground source heat pump through coaxial borehole heat exchanger

The accurate calculation for heat flux of borehole heat exchanger (BHE) is of great importance for design of ground source heat pump (GSHP); the climatic conditions influence GSHP performance through GHE. In this study, a 2-D heat transfer model for coaxial BHE was built to investigate the effects of multi-climatic parameters on BHE heat transfer and GSHP performance. The outlet temperature, ground temperature profiles and COP of GSHP system for the cooling period were concerned. The effects of climatic conditions under different borehole depths, ground thermal conductivities and flow rates were studied. The studies showed that the outlet temperature from BHE increased about 10% and system COP declined about 5% in cooling mode with considering the effect of climatic conditions. The comparison indicates that the effects of climatic conditions on coaxial BHE are stronger than that on U-tube BHE. Generally, the climatic conditions influence BHE heat transfer mainly through the shallow ground and the influences strengthen with time. The effects can be more significant with a larger ground thermal conductivity, but it weaken with increase of borehole depth. Also, the effects of climatic conditions on BHE and GSHP seem to be independent of flow rate.

Automated summary

Accurate calculation of heat flux for borehole heat exchanger (BHE) is crucial for ground source heat pump (GSHP) design, and climatic conditions affect GSHP performance through ground heat exchanger (GHE). A 2-D heat transfer model for coaxial BHE was created in this study to investigate the impact of multiple climatic parameters on BHE heat transfer and GSHP performance. The study focused on the outlet temperature, ground temperature profiles, and COP of GSHP in the cooling period. The results showed that considering the effect of climatic conditions, the outlet temperature from BHE increased by about 10%, and system COP decreased by about 5%. The study also found that the effects of climatic conditions on coaxial BHE were stronger compared to U-tube BHE. Generally, climatic conditions mainly influence BHE heat transfer through the shallow ground, and the impact strengthens over time. The effects can be more significant with higher ground thermal conductivity but weaken with increasing borehole depth. Additionally, the effects of climatic conditions on BHE and GSHP appear to be independent of flow rate.