Comparison Of Heat Transfer Performance Of Vertical U-tube Buried Heat Exchanger Under Different Conditions

The solar energy coupled ground source heat pump(SGSHP)system at the cost of economy can alleviate the geothermal imbalance caused by long-term operation of ground source heat pump(GSHP)system.Firstly,the accuracy of the physical model is verified by the data of the soil thermal response of the actual project.Secondly,FLUENT software was used for simulation analysis to compare the soil thermal performance and buried pipe heat exchange performance of the GSHP system and SGSHP system in different conditions,so as to obtain the optimal economy and heat exchange performance.Finally,a GSHP project of a practical project in Hebei province is measured and analyzed.The final evaluation index of the system will show up after analysis of the economy and efficiency of the system in the practical project.Specific studies are as follows:(1)GAMBIT software was used to build the buried tube heat exchanger model,which was simplified.Then the data of soil thermal response test is used to verify the accuracy of the simplified model,so as to ensure the accuracy of simulation.(2)FLUENT software was used to simulate the influence of spacing,backfill material,and flow rate of buried pipes on heat transfer performance of buried pipes and soil thermal performance.It is concluded that the heat exchange performance of buried pipe heat exchanger will be improved when the spacing of buried pipe is 5.2 meters,the backfill material sandy soil,and the inlet flow rate 0.9 m·s-1.By comparing the performance of two systems,the conclusion can be drawn that the GSHP system is more affected by these three factors.The optimal heat exchange performance of the heat exchanger and the economic performance of the system can be obtained through changing the influencing factors.(3)The performance of the GSHP system in Hebei province was monitored for one year.The results showed that the system had good performance in the first year of operation,with indoor temperature and humidity meeting human needs.A total of 1131 T standard coal was saved,4641 t CO2,37.58 t SO2.and 18.9t soot emission was reduced.The system has remarkable energy saving capacity and has made great contribution to environmental governance.To sum up,when three kinds of optimal buried pipe influencing factors are adopted,the heat transfer performance of GSHP system can be significantly improved,the gap withSGSHP system can be narrowed,and the initial investment of the system can also be reduced.The actual GSHP system has excellent performance,remarkable energy-saving effect,and also meets the requirements of human thermal comfort.However,SGSHP heating system will reduce the system economy and can not effectively alleviate the soil heat accumulation.The results of this study provide guidance for practical projects,and the GSHP system should be preferred in large buildings.