Study On Influencing Factors Of Accuracy Of Soil Thermal Properties Identification In Thermal Response Test

With the rapid development of economy and society,the contradiction between energy supply and demand and human development has become increasingly fierce.Under this background,the development of renewable energy source,the reduction of consumption in fossil energy,the increase of energy effective utilization and the reduction of emissions of nitrogen oxides and other pollutants has become the important support point for the national energy development strategy.The ground source heat pumps system can achieve the purpose of energy saving and emission reduction through the importation of a small number of high-grade enrgy to drive the low temperature energy.It is recognized as a highly efficient energy-saving heating and cooling air conditioning system.Although the ground source heat pump system has unparalleled development advantage,its development is still constrained by a lot of factors.Firstly,the initial investment of the ground source heat pump system is too high.Leading to the most of the construction companies is difficult to bear the initial investment which limit the promotion and development of the ground source heat pump system.Secondly,the soil thermal physical parameters are the guiding parameters for the design of ground source heat pump system.Its accuracy will directly affect the design of the ground source heat pump system.And then affect the economic efficiency and long-term performance of the system.Thus it can be seen that the accuracy of the soil thermal physical parameters in the construction area is very important for the application of the ground source heat pump system.In this paper,the heat transfer process of buried pipe heat exchanger,the key components of ground source heat pump system,with the surrounding soil were analyzed based on the principle of thermal response test.And then the mathematical modeling of the underground heat transfer process is carried out by using CFD knowledge,and established a simulation experiment platform by using the Fluent.The accuracy of simulation experiment platform was verified by setting up experimental platform,measuring key position temperature,comparing with the simulation results and analyzing of the causes of the change of relative error.A variety of factors affecting the accuracy of thermal physical parameters were summarized with the theoretical analysis.Numerical simulation was carried out by using the simulation platform,getting the temperature of the inlet and outlet at one time under different conditions.For the purpose of simulating the thermal response testing process,the inlet temperature of the buried pipe heat exchanger was managed with UDF.Using Matlab to compile parameter identification program for line heat source model and the column heat source model separately based on the parameter optimization.After obtaining the thermal response test data,the data is imported into the parameter identification program and run it.the soil thermal physical parameters under the influence of single factor was identified.on this basis,analyzing the identification error of soil thermal physical parameter.the best test time is presented according to the minimum relative error.discarding the traditional project based on subjecetive experience to determine the method of testing time,it is recommended in accordance with the best test time for thermal response test arrangements.and by analyzing the influence of various factors on the identification of the best thermophysical parameters,the paper gives the reasonable suggestions on the selection of construction site and the operating conditions during the thermal response test,and provides guidance for ground source heat pump engineering practice.