Parametric Analysis Of Thermal Interference For Vertical U-Tube Geothermal Heat Exchangers

Ground source heat PumP(GSHP) air conditioning system utilize ground soil as a heat source/sink,achieve heat transfer between the ground soil and a working fluid (water or anfifreeze solution) circulating in a closed loop buried in the ground. Compared to other conventional alternatives,the ground source heat pump system makes full use of renewable energy,and boasts the features of protecting the environment and reducing electric power consumption.It has been applied in Europe and American to also in China,and a few GSHP pilot projects have been completedhere.U-tube groud heat exchanger in ground source heat pump system uses the heattransfer between U-tube and the earth to achieve heating and cooling requirements. By using the earth as a heat source and heat sink,the hot heat was removed from the system to the soil through the heat transfer between the fluid of U-tube and the soil in summer ,while the hot heat was removed from the soil to the system in winter. In fact,because the space between the two U-tubes is small,the temperature differences exist between the two pipes, the reflux heat situation is bound to happen between the two pipes when the fluid flow from one pipe,after heat exchange with the soil,to the other pipe.The phenomenon have the effect of the heat exchange which is called hot short-circuit situation. Hot short-circuit situation should be pay special attention to in the design and installation of the vertical U-tube heat exchanger.But there are less studies of the effect of hot short-circuit situation.In the paper,based on test data of a U-tube heat exchangers in ground source heat pump project in Chengdu,analyse the test results of the effect of hot short-circuit situation in summer and winter conditions,set up he three-dimensional heat transfer model of U-tube heat exchanger using the energy balance method,divide the heat exchange of the vertical U-tube heat exchanger into two zones.One is called boreholes,the other is called boreholes outside to the unlimited distance.Through a comparative analysisi of the simulation results and the measured results, correction model repeatedly to verify the model method and the credibility of results.In the paper, study the hot short-circuit characteristics of the U-tube heat exchanger through theoretical analysis, test research, numerical simulation methods.Analyse various factors on the impact of the hot short-circuit of the U-tube heat exchanger,containing velocity, branch spacing, drilling size, backfill materials,, branch insulation baffles,and so on. Propose measures to reduce the hot short-circuit and basic data for ground source heat pump system design.