Study On The Effect Of The Identification Method Of Soil Thermal Properties On The Long Term Operating Performanceof GSHPS

Energy consumption for building heat,ventilation,refrigeration and domestic hot water is about 30%of the social total energy consumption in China.In northern cities and towns,the demanded heat in house is more and the building energy consumption will be more prominent because winter is colder and longer.In order to reduce energy consumption and improve the efficiency of energy and resource,China’s 13th Five-Year Plan put forward new requirements for the global climate change,and provided clear guidelines and long-term plans for the development and utilization of geothermal energy.The ground source heat pump system(GSHPS),as an advanced techenology for the geothermal energy,has received extensive attention and strong promotion because of its energy saving and environmental protection characteristics.The soil thermal properties,which are the basic parameters for the design of the GSHPS,determine the total length and exchange performance of the gorund heat exchangers and thus play a vital role in the construction and operation cost and operation performance of the system.The thermal response test(TRT)is a common method for identifying soil thermal properties in engineering,but its mathematical model treats the actual complex stratified soil with groundwater as the homogeneous soil without groundwater.Although the short-term heat exchange capacity of the two soils may be similar(the heat is transferred from the ground heat exchangers to the soil when the TRT is doing),but its impact on the long-term performance of the GSHPS needs to be studied.Therefore,to appropriately and reasonably evaluate the influence of the identification method of the soil thermal properties on the long-term operating performance of the GSHPS,the research of this paper will start on the following steps:Firstly,a three-dimensional numerical simulation experiment platform for the GSHPS was established.Based on the platform,the thermal properties of soils were identified under different geological conditions,and the equivalence of TRTs was discussed.First,the effects of groundwater seepage on the identification results of the equivalent thermophysical parameters of soils were studied under different groundwater seepage conditions.Second,multi-factor analysis of the TRTs was conducted under different conditions.Third,the equivalence of the TRTs was discussed under the seepage condition.The difference of the heat transfer performance of the ground heat exchanger under the actual seepage condition and the theoretical equivalent condition was discussed.Secondly,a typical building in Harbin was selected as the simulation object of this paper.The numerical simulation model of the GSHPS was built based on the analyzed building load,and the annual building load was written by program to realize the dynamic operation of the system in long term.Under the actual seepage conditions and theoretical equivalent conditions of different soil geological conditions,the long-term operation of the GSHPS was simulated,and the soil temperature,the inlet and outlet temperature of the buried heat exchanger and the operating performance of the system were observed.Finally,the above research was further extended under different building loads and backfill materials to judge the difference between under the actual seepage conditions and the theoretical equivalent conditions to discuss the influencing factors.Moreover,the long-term operation of the GSHPS was simulated under the condition of soil stratification without seepage and its equivalent homogeneous non-seepage conditions.The influence of soil stratification and equivalent conditions on the operation performance of the GSHPS was analyzed.