Influence of ground heat exchanger zoning operation on the GSHP system long-term operation performance

Abstract

To alleviate the ground heat accumulation after long term running of ground source heat pumps (GSHP), ground heat exchanger (GHE) zoning operation can be adopted. Two GHE operation modes - zoning operation and full running - are compared in a case where heat release to the ground in summer is larger than the heat extraction from the ground in winter. In this study the soil thermal conductivity, volumetric specific heat capacity, borehole depth and spacing are 2.0 W(mK)-1, 5.0x106 J(m3K)-1, 100m and 5m respectively with the boreholes arranged in a square 20x20 array. Under the given conditions the simulation results show that GHE zoning operation depresses the increase in amplitude of GHE outlet water temperature and so that the GSHP systems operate normally throughout the whole service life. By adopting GHE zoning operation, the energy consumption of the GSHP system is found to be reduced compared with that of a GHE operated without zoning. Operation without zoning shows that the GHE summer outlet water temperature increases faster than that with zoning operation and power demands are increased for the given GSHP load. Furthermore, in this case, the GSHP would not be able to run normally in the last several years due to the condensing temperature exceeding its upper limit.