Optimization Of Heat Transfer Analysis Calculation Method And Research On Zoning Operation Of Ground Heat Exchanger

As an important part of the ground source heat pump(GSHP)system,the ground heat exchanger directly affects the operation performance of the GSHP system.At present,the widely used heat transfer calculation and analysis methods usually ignore the impact of soil temperature variation on the load of each buried tube.So it probably affects the analysis accuracy of long time GSHP operation.Besides,nearly all GSHP operation modes are full open and stop,even under partial load,the buried tubes are all put into operation.In this kind of operation mode,thermal accumulation of in the central area of the buried pipes will reduce the overall efficiency of the GSHP system,and even influence its normal operation.According to this,this paper conducts research on the heat transfer analysis calculation method and zoning operation feasibility of the GSHP.In this paper,the self-adaption load distribution method is used to analysis and calculate the heat transfer process of the GSHP.This calculation method considers the actual influence of soil temperature variation on thermal load allocation of each buried pipe during the operation of the system,and eliminates the defect induced by the assumption that all every buried pipe has equal load.Calculation results show that,heat exchange capacity of each buried pipe is not equal after long-term operation.Because the heat dissipation condition of the buried pipes in the side area is better than that in the central zone and bear more thermal load.After 20 years of operation,the soil temperature distribution in the GSHP area is still relatively uniform.This indicates that the common believes that long-term operation of GSHP will have serious cold or heat accumulation problems in the central area is debatable.Because inlet water temperature of the buried pipe needs to be calculated at every moment,the calculation process of the self-adaption load distribution method is more complicated and time costing.To solve this problem,this paper simplifies the calculation process of the selfadaption load distribution method by modifying the calculation form of the temperature response function,reducing the space calculation domain and time calculation domain,and improving calculation algorithm,which greatly reduces the calculation time.When modifying the temperature response function calculation form and improving algorithm,the error of the calculated result is very small and can be applied to any conditions.Though the error of the calculated results is small,reducing space calculation is only applicable to simplify calculation of GSHPs with large areas.For the calculated results would have relative large errors,the method of reducing time calculation domain is only suitable for cases with long operation time.Therefore,for cases with very high calculation accuracy requirements,it is recommended to simplify the calculation process by modifying the calculation form of the temperature response function,improving calculation algorithm,and reducing the space calculation domain.This article takes a building in Jinan as an example,and analyzes the impacts of the zoning operation of its GSHP on the system performance based on the optimized calculation method,and compares it with those of the non-zoning operation mode.The results show that,compared with non-zoning operation,zoning operation can alleviate the accumulation of cold or heat in the soil in the buried pipe area to some extent,suppress the circulating fluid temperature increase in buried pipes in summer,and extend the GSHP normal operation time.At the same time,it can effectively reduce the power consumption,cut down operation costs,and decrease exhaust emissions.