Research On Soil Thermal-physical Test Methods And Influence Factors

Ground source heat pump(hereinafter called GSHP) air conditioning system, as a kind ofenergy-saving, environmental friendly technology, has been more and more widely applied inthe field of architecture. Design of ground heat exchanger is the key step in the GSHP design.Accurately testing the thermal-physical parameters is the premise and guarantee of the groundheat exchanger design. The paper conducts a series of analysis and research on related issuesof ground thermal-physical property test and mainly in the following aspects.First of all, in this paper, the testing methods and data processing methods are analyzedand compared to recommend a method applicable to engineering. This method is based on thethermal response test, first calculating comprehensive coefficient of thermal conductivity ofthe rock-soil, then, using double parameters estimation method to calculate the boreholethermal resistance and thermal diffusion coefficient of rock-soil. Secondly, based on thethermal-physical parameters calculation method of rock-soil recommended in this paper, thefactors that may cause the testing error are analyzed. Study indicates that when the deviationof the primitive rock temperature test is0.5℃, borehole thermal resistance deviation couldbe as high as6.5%, and the average deviation of heat transfer per unit length is2.5%insummer and7.5%in winter. Rock-soil comprehensive coefficient of thermal conductivity willincrease with heat power rising. With every deviation of100W in the heating powermeasuring value, borehole thermal resistance decreases0.01mk/w on average, and thedeviation of heat transfer per unit length is about1.9%in summer and2.0%in winter. Bycalculating test data of different length of time, the recommended length in actual engineeringtest will not be less than36hours.What’s more, based on the traditional expression of test results, this paper introduces arectangular wave step load and the superposition principle, and verifies the accuracy of theheat transfer model. Combined with the heat transfer model in this paper, a formula wasproposed so that the thermal-physical parameter will be directly applied to the length of theground heat exchanger design.Finally, this paper studies the phenomenon of power cut during the test. By applying theheat transfer model which combines the rectangular wave step load with the superpositionprinciple, the author uses the parameter estimation method, ignoring waiting process andmeasuring directly. This method can be used to calculate the thermal-physical parameters of test wells in case of power cut and is verified. This paper argues that this kind of method tocalculate the thermal-physical parameters can satisfy the precision requirement in engineering,so it is with very meaningful and practical value.