Study Of The Influence Of Power Cuts On Rock-soil Thermal Response Test

The cost of boring heat-transfer hole and paving U-type buried pipes will account for one third of the ground-source heat pump system. So, it has been one restraining factor in the system development . Whereas the thermal conductivity of rock-soil is an important basic parameter of the design of the ground heat exchanger. And there will be 4.5~5.8% deviation on the design length of the ground heat exchanger if it has 10% offset of the thermal conductivity. Therefore, it directly impacts the initial cost of the ground source heat pump system that whether the thermal conductivity is accurate or not. At the same time, the volumetric heat capacity affects the work, especially the change of operating conditions, of the ground source heat pump system. Therefore, to get more accurate parameters of the thermo-physical properties of rock-soil, this paper researches the influence of starting heat time, time of power off and bore diameter on the thermal conductivity and the volumetric heat capacity of rock-soil in the Thermal Response Test.In ASHRAE handbook, it is ruled that it is needed to wait that the temperature difference between the U-type circuit and the initial ground temperature is not more than 0.3K if the whole 48 hours test is completed and it needs to test again. For the layer whose thermal conductivity is middle or big(λ≥1.7 W/m·K),the waiting time needed is 10~12 days while 14 days is needed for the layer whose thermal conductivity is small(λ<1.7 W/m·K). The waiting time can be shortened if the completed test time is short. It is calculated with computation program that the waiting time which is needed for the completed 1~36 hours test, with different bole diameters and the three layers whose thermal conductivities are big, middle and small, which is stopped for power cut and needed to test again.Based on the propsed model accounting for heat transfer between a buried geothermal heat exchanger and the ground with unsteady input power, and combined with parameter estimation techniques, it can be got that the parameters of the thermo-physical properties of rock-soil in unsteady input power with writing computation program in this paper. And it is proved with experiment that the method is correct. The findings indicate that this measurement method greatly reduces the demand of the stability of heating power in the Thermal Response Test and is more practice for engineering application. It is got from the results that the waiting time which is needed for the completed 1~36 hours test, with different bole diameters and the three layers whose thermal conductivities are big, middle and small, which is stopped for power cut and needed to test again. At the same time, it is got that the method of calculating the thermal properties of rock-soil with unsteady input power.