Research On Heat Storage Technology Of End Bearing Energy Piles In Different Soil Media

Ground source heat pump(GSHP)is a clean and renewable energy technology.Energy pile is an economical and efficient energy saving and emission reduction technology composed of ground source heat pump technology and buried pipe heat exchanger on pile foundation.It is a new buried pipe method of ground source heat pump technology.It places the heat transfer device that should be laid by buried pipe in the pile foundation of the building,and forms the heat transfer system through pile foundation and underground soil,which saves the cost and land area of drilling and greatly shortens the construction period.The end-bearing energy pile is based on the energy pile,adding heat exchange body on the outside of the foundation pile,so as not to destroy the structure of the foundation pile,and more efficiently play the heat exchange capacity of the traditional energy pile.In this paper,a THREE-DIMENSIONAL finite element model of end-bearing energy pile was established based on the finite element software ANSYS to detect the heat transfer effect of end-bearing energy pile in different soils and carry out simulation calculation.A small soil heat transfer system test bench was designed and built to verify the simulated data for analysis and comparison.Changchun,this article selects the typical local three soil test comparison,due to differences in soil around,can’t use the literature data,the soil should be taken before the simulation of selected very soil parameter determination,again through the test and simulation soil,choose the best heat transfer,heat accumulation effect for pile end bearing energy transfer system in the process of application provides the theory basis for design and operation.In this paper,the development history and research status of energy pile are summarized,and the experimental research of energy pile system is analyzed and summarized.On this basis,the end-bearing energy pile system is simplified and the heat transfer between the heat exchanger body and the soil is simplified into the heat transfer between the heat source and the soil.A model was established to simulate the heat transfer of different soils,and a small soil heat transfer system testbed was built to study the heat transfer characteristics of different soils in the end-bearing energy pile system.The design idea of the test bed is to establish the CFD model of the traditional energy pile for numerical simulation,and determine the specific size of the end-bearing energy pile model.The model of end-bearing energy pile is scaled down to build a small test bed.The structure of the small test bed is0.5m*0.5m*0.5m cube,and the outside is wrapped with insulation materials.In the test soil box,a vertical cylindrical dry-fired electric heating tube is buried along the center of the body,and various physical parameters of the soil are measured and analyzed in detail.Detailed design and selection of insulation layer,thermocouple and other major equipment components,temperature measurement and acquisition and correction are controlled by intelligent data acquisition instrument.Through the small test bed built,three different groups of soils were tested and operated respectively in clay,silty and sandy soil,the change of heat transfer efficiency of different soils under the same working condition was obtained,and the influence of various physical properties of different soils on heat transfer of end-bearing energy pile in different soils was emphatically analyzed.The results showed that the three soils showed different heat transfer efficiency due to their physical properties.When the heat transfer system reached equilibrium,the clay had the highest heat transfer efficiency among the three soils.In the study of intermittent operation of energy pile system under different soil media,through the analysis of temperature variation trend of different horizontal distance between soil and heat exchanger,it is found that with the increase of operation time,soil heat transfer efficiency decreases gradually.Through the heat transfer test of three kinds of soils,it is found that the heat transfer efficiency is highest when the start-stop ratio is 1:1,and the heat transfer efficiency is highest when the start-stop ratio is 1:2.Under the same conditions,the temperature recovery rate of clay was slower than that of the other two soils,indicating that clay had better heat storage performance.Through the comparison of experimental data,the soil recovery rate of different soils under the same operation mode was significantly different.Based on the experimental analysis of which operation modeshould be selected for different soils,the following conclusions are drawn: under the same working condition,there is an operation mode suitable for different soils to achieve the highest heat transfer efficiency.Sand is suitable for 12-hour intermittent12-hour operation mode.The silty soil is suitable for 8-hour intermittent 4-hour operation mode.Clay is suitable for 12-hour intermittent 6-hour operation mode.