Experimental Research On Deep Buried Vertical U-Tube Ground-Coupled Heat Pump Running In Winter And Three-Dimensional Simulation

Ground-source heat pump systems have been widely applied to both residential and commercial heating and cooling in America and Europe as these systems can make significant contributions to reductions in electrical energy usage and have been recognized as an environmental-friendly alternative to conventional unitary system. However, this technology has seldom been adopted so far in our country. Many a work of research on GSHP and popularizing application need to be done. Vertical U-Tube ground-coupled heat pumps have become increasingly popular because of many outstanding advantage it has, such as: fewer area requirement, fewer limits, running steadily, better performance, lower costs on system maintenance etc. The subjects presented in the first chapter focus on the principle, construction, advantages of GSHP system and heat transfer model of vertical U-Tube ground-coupled heat pump.One month experimental testing on undisturbed ground temperature and three months experimental testing on single U-Tube GCHP heating operation has been performed. The equations for calculating the undisturbed ground temperature in Chongqing have been given in this paper. In order to study on the law of ground heating transfer, several different flow rate of U-Tube were applied for experimental testing. According to the different flow rate of pipe, four phases of experimental testing had been divided. GCHP system cycled at nighttime and stopped at daytime in the first three phases. The ratio of on-off time is 5:7. The average quantity of heat per meter of the borehole and coefficient of performance of the system are 57.64w/m and 4.10w/w respectively in the second testing phase that the GCHP system cycled at 750 L/h flow rate of U-Tube. GCHP system cycled allday in the fourth phase at 750 L/h flow rate of U-Tube . The average quantity of heat per meter of the borehole and coefficient of performance of the system are 46.23w/m and 3.49w/w respectively in this phase.According to analysis of the testing results, the effects of thermal short-circuiting between two legs of the U-Tube become more serious with the operation time increasing. The effects of thermal short-circuiting become from 2.0% at first phase to 7.1% at fourth phase.A transient three-dimensional numerical model based on the thermal balance of finite control volume has been developed for the simulation of heat transfer over avertical U-Tube ground heat exchanger. The predicted data calculated by the model agreed reasonably well with the experimental data.The isotherms in and around the borehole of the vertical U-Tube have been created by MATLAB 6.1 according to the simulated data. The temperature distribution around the U-Tube and the variation of impactive radius can both be showed directly though these charts.