Exhaustive Search Method To Determine Ground Thermal Properties And The Accuracy Analysis

Ground Source Heat Pump(GSHP),which utilizes the shallow ground geothermal energy effectively,is developed rapidly due to its advantages of less pollution,high efficiency and longevity.Ground thermal properties measuring technology plays a key role in rationally designing ground heat exchangers(GHE),cutting down initial investment,and improving operation efficiency.Thermal response test in situ with constant input power is the main method to obtain the ground thermal properties.However,even today there is still no well accepted conclusion on how long the test duration should be.For a certain engineering project,the test time is usually set according to the tester's experience than the actual need to obtain the accurate results of the local ground,therefore,it may obtain inaccurate test results.In addition,the optimization method which is usually used in determining ground thermal properties,in general,can gain ground thermal conductivity with high accuracy,but it sometimes cannot acquire high reliable ground volumetric heat capacity and borehole thermal resistance.To accurately determine all the ground thermal properties,this thesis has proposed to adopt the exhaustive search method in determining ground thermal properties.Simulation shows that the three-parameter estimation method is more accurate than two-parameter estimation method.Calculation with line source model is faster and more accurate than that with cylindrical heat source model,thus it is more suitable for engineering applications.Simulation,experiment and engineering test show that the exhaustive search method get ground thermal properties more credible compared with the genetic algorithm,complex algorithm and ant colony algorithm.A test software to calculate ground thermal properties is developed.The software can calculate ground thermal properties and analyze their accuracy in field test.It can also automatically send test termination signal when the test results meet the demanded reliability.This will avoid getting inaccurate results due to improper test time set.