Study On Zoning Operation Strategy Of Multi-borehole Ground Heat Exchangers

Ground source heat pump(GSHP)system is widely used for its high efficiency and environmental friendliness,but it would not work at efficient state or even failure if the ground temperature increase or decrease greatly with running time increasing.For example,when the heat extraction and injection of a borehole heat exchanger(BHE)is not seasonally balanced,ground heat/cold accumulation will occur in the central area of the buried field and cause a decline of the GSHP's operational efficiency after the long-time running.Recently,BHE zoning running method is proposed to alleviate the heat/cold accumulation,but it is far from perfection and still need to be studied.In this paper,several zoning running strategies are proposed and the main aim is to maintain the heat extraction and injection of running boreholes in the most balance.Take a case that the load in summer is greater than that in winter,this thesis has calculated the soil temperature distribution of a 12×12 GHE field and analyzed the influence of the summer and winter load ratio?soil thermal parameters and tube spacing.The results show that the GSHP systems can operate normally in 20 years with no GHE zoning running when the summer and winter load ratio is less than 1.5:1.When the summer and winter load ratio ranges in 1.5:1-2:1,it is suggested to adopt the GHE zoning running method which all buried pipes are put into running in the high load season and stop running of the far most outside rows of the boreholes in the low load season(i.e.strategy two).The greater of the summer and winter load ratio,soil volume specific heat and tube spacing is,or the smaller of the soil thermal conductivity is,the less heat accumulation is in the central area of the boreholes field with GHE zoning running.When the tube spacing,soil volume specific heat and soil thermal conductivity are small,it is recommended to stop running of the two far most outside rows of the boreholes in the lowload season(i.e.strategy three).When the tube spacing,soil volume specific heat and soil thermal conductivity are large,it is recommended to adopt the zoning running method of strategy two.