Construction And Research Of Vertical Ground Source Heat Pump System Model Coupled Thermal Conduction And Groundwater Seepage

As a kind of clean and renewable energy with huge reserves,shallow geothermal energy has gradually become a new choice for the world to cope with the energy crisis.Ground source heat pump technology is a new type of heat pump technology that buries heat exchangers in the ground and directly acquires shallow geothermal energy.It has remarkable advantages such as high efficiency,energy saving,environmental friendliness and multi-purpose use.The buried pipe of ground source heat exchanger is the key content of the research on ground source heat pump technology.In the past research,only the heat conduction effect of the ground heat exchanger and the soil was considered,and the groundwater seepage in the soil was neglected.The impact of the design of the buried pipe is too long,and the initial construction cost is too large.In this paper,the effect of groundwater seepage on the performance of vertical buried ground source heat pump system is studied by using the outlet fluid temperature and soil average temperature as the evaluation conditions.Firstly,the heat transfer model of the traditional vertical buried heat exchanger is analyzed to discuss how the buried pipe exchanges heat with the surrounding soil.Then based on the basic theory of soil porous media,the influence of groundwater seepage is added during the heat transfer process,and the mathematical model of the vertical borehole heat exchanger under the thermal-permeability coupling is established,and the numerical solution of the model is obtained by the finite difference method.Based on the original Utube heat exchanger module in the design software,a vertical buried-tube heat exchanger module considering the influence of groundwater seepage is established.In order to verify the accuracy of the module,the inlet and outlet fluid temperatures of the existing sandbox experimental device were simulated,and the error between the simulation results and the experimental results was within ±0.5 °C.The verification results were good.Finally,combined with the actual project,a geothermal heat pump system with hotinfiltrated coupling and vertical buried pipe was built in software,and the whole-time simulation was carried out in the presence or absence of groundwater seepage.The results show that groundwater seepage can improve the outlet fluid temperature in the heating season and reduce the outlet fluid temperature in the cooling season.Annual average outlet fluid temperature is reduced by 0.36?.The groundwater seepage can strengthen the heat exchange capacity of the buried heat exchanger,but also can weaken the cumulative effect of heat/cooling in the soil,making the change of soil temperature is smaller.In addition,the 10-year simulation operation of the ground source heat pump system is carried out under 6 working conditions of different groundwater seepage velocity and soil porosity.The results show that for the system with uneven cooling and heating load,with the increase of groundwater seepage velocity,or the soil porosity increases,the heat exchange capacity of the buried tube heat exchanger increases,and the cumulative effect of heat/cooling in the soil is weakened,which is more conducive to long-term operation of the system.