Research On Distributed Soil Thermophysical Property Measurement Technology For Ground Source Heat Pump

As an efficient energy saving technology using renewable energy,ground source heat pump(GSHP)is widely used in China.Buried tube heat exchanger is an important part of the ground source heat pump system.The main factor affecting the design of buried pipe heat exchanger is the soil thermal property parameters,which are mostly obtained by the geotechnical thermal response test.At present,one-dimensional heat transfer model is used in most of the soil thermal physical property tests in China.This model does not consider the stratification characteristics of the actual underground soil,and also ignores the underground seepage.In practical engineering applications,the problem of poor reproducibility of the test results of thermal properties often occurs,which hindering the popularization and application of ground source heat pump technology in China.In this paper,based on the mean heat transfer model,a vertical u-shaped buried pipe layered heat transfer model and a seepage model are established to study the thermal properties of the soil around the buried pipe.Firstly,the distributed soil thermophysical property testing program was written according to the two-parameter method,and then the subsurface soil was stratified according to the geological condition and seepage condition of the soil,and the thermophysical property parameters of the layered soil were fitted by the change of water temperature at the entrance and exit of each layer.The values of the thermophysical parameters of the soil were taken into the layered model established in ANSYS for simulation calculation.It was found that the relative error of the outlet temperature of the layered physical parameters and the average physical parameters in the non-seepage condition was 6.9% after 48 hours of system operation.The relative error of outlet temperature between layered soil thermophysical parameters and average soil thermophysical parameters under seepage condition is 12.7%.It can be seen that the relative error of the simulation results of layered thermophysical parameters and average thermophysical parameters is larger than that of the non-percolation condition.In order to further verify the reliability of thermal physical parameter value stratification,soil thermal physical property of the measured holes into the calculation,the calculation results show that outlet temperature of the thermal physical parameters of layered peace soaking outlet temperature of the outlet temperature of the physical parameters and the measured hole relative error of 2.7% and 9.1% respectively,the single well in heat relative error of 2.6% and 9.3% respectively.It can be seen that the values of thermal physical property parameters of stratification are closer to the real values of soil thermal physical property parameters than the values of average thermal physical property parameters.If this method is extended to the geotechnical thermal response experiment,the results of the thermal response experiment will be closer to the real thermal physical parameters of the soil,so as to effectively reduce the initial investment of buried pipe heat exchanger,and further promote the popularization and application of ground source heat pump technology in China.