Three-Dimensional Dynamics Research On Vertical Heat Exchanger Performance Of Ground Source Heat Pump Under Coupled Heat Transfer Inside And Outside Of Pipe By Programming

Ground-source heat pump system(GSHPS) is a new energy efficient technology of renewable energy, this technology has been highly concerned and widely used in recent years. Heat exchanger is the core aspect of ground-source heat pump system. The heat exchangebetween the circulation medium and the surrounding soil will affect the running performance of the ground-source heat pump system, relating to the better matching problem between heat exchanger designand building loads, which decides the whole buried pipe system’s initial investment and operating cost. Therefore, the study of the heat transfer performance of ground heat exchanger is particularly important.There are analytical, numerical and experimental three main methods to research heat transfer performance of GSHPS. However, to solve this problem by numerical method than analytical method is closer to real condition. Beside, it will save more money and time thanby experiment. More important, this method is widely used in the research filed of GSHPS. Numerical method includes commercial simulation software and self-programming. Apparently, using commercial software is more convenient to carry out numerical simulation, and it is operated more easily. But we couldn’t modify the internal calculation details for special problems. Due to the actual soil is porousmedium, when we research heat and mass in porous medium, the existing commercial software is limited in many aspects. Therefore, this paper has researched thermal seepage coupling problems of the soil source heat pump vertical buried pipe by programming.Based on the soil porous media and fluid dynamics theory, the mathematical model of heat and mass transfer is established for heat transfer of underground vertical buried tube heat exchanger. Forther more, a three-dimensional dynamic numerical calculation program is designed for this model by using FORTRAN language, Fortran PowerStation4.0 is selected for debugging platform. The program is applied to simulate the geotechnical thermal response test, comparing the results of the simulation with the test to verify the accuracy and reliability of this program.Due to the radial size of the pipe is far less than the entire calculation area, and the flow offluid in the pipe is very complicated, the circulating water of the vertical buried tube is often simplified as a constant heat flux of the wall or uniform flow rate of the section in the study of GSHPS. In order to closer to the real situation, this program takes into account heat exchanger which coupled three dimensional turbulent flow in the pipe and the surrounding soil, the calculation and analysis platform is established for the coupling heat and mass transfer of geotechnical porous medium. In addition,the comparison and analysis of he error effect of the performance of heat-exchanger is made by using the programming when assuming uniform flow field and turbulent flow field. The conclusion is drawn there is a big error in the results of assuming uniform flow field, therefore, the calculation and analysis of borehole heat exchangers should consider turbulent flow field to achieve the coupling calculation of inside and outside the pipe. Accordingly, this paper considersheat transfer which couples turbulent flow field in the tube with the surrounding soil, and the influence of groundwater seepage, inlet flow velocity in buried pipe, inlet temperature of the circulating water, as well as backfill material on heat transfer performance are further analyzed. The results have shown that the better the soil seepage velocity, the greater the heat transfer effect;When the inlet flow velocity is low, increasing velocity can significantly improve the heat transfer effect, when flow rate increased to 0.9m/s, the increase ofvelocityis not conducive to heat exchange;Increasingthe inlet temperature of the buried pipe and the coefficient of thermal conductivity of backfill materials can improve the heat transfer effect.The purpose of this study provides programming method for the in-depth study of buried tube heat transfer performance.