Study On The Insitu Soil Thermal Response Test Data Processing Methods Of Double U-tube BHE

Ground source heat pumps make use of geothermal energy in shallow soil to servethe air conditioning system of buildings, this technology is widely concered at homeand abroad because of energy-saving. Heating exchange of ground heat exchanger is themost important aspect of ground-source heat pump system, the size and heat transferperformance of ground heat exchanger directly affect the initial cost and itsperformance.To ensure the heat exchanger design and buliding loads better match, the accuratethermal conductivity of rock-soil must be obtaind. Combined with practical engineering,a ground thermal response test of single U-pipe and double U-pipe is done at the city ofMian Yan in Si Chuan Province. For the processing and analysis of experimental data,there are many theoretical models and data processing methods, but the only oneanalysis methods for single U analysis of the heat exchanger is introduced in the"Technical code for ground-source heat pump system". But in the actual project, thedouble U-pipe heat exchanger is applyed more widely, apparently,its analyticalsolutions expression doesn’t match with the analytical solutions of single U-pipe. Forthis problem, the thermal conductivity, the volumetric heat capacity of the soil and theresistance of borehole interior were obtained by curve fitting method of theexperimental data and by double parameter estimation method respectively. doubleparameter estimation method based on the combination of three different interiormodels and borehole exterior models for double U-pipe heat exchanger systems. And the result was brought into the derivation analytical models to anti-launched buriedaverage temperatures，and compared with the average temperatures which measured inthe engineering to find the best data processing and analysis methods of double U-pipeheat transfer coefficient. In addition, the influence of testing time, backfilled material,the distance between two U type branch tubes and borehole diameter on the resistanceof borehole interior were analyzed by using the double parameter estimation methodbased on these three models. It is found that abandoning the initial ten hours test data, isgood to improve the stability of analyzed results.Finally, the test data was analyzed by using numerical simulation method. Thesimulation results of the outlet temperature based on these three models mentionedabove were obtained by the input of soil thermal physical parameters analyzed to theestablished three dimensional models (equals to the actual size). The influence of theinlet velocity and temperature and the initial soil temperature on the heat transfercapacity of the buried tube, the buried tube heat transfer capacity in the ground ofdifferent parameters was computed, and the heat transfer performance was analyzed byconsidering the soil temperature distribution. The result can be referred for the design ofthe practical ground source heat pump systems.