Test Of 50-meter-deep Buried Vertical Tube For GSHP In Cooling Operation Mode And Cylindrical Heat Source Model

After the research about performance of shallow buried vertical ground heat exchanger and horizontal ground heat exchanger in cooling and heating operation , the paper will continue to discuss the performance of 50-meter-deep buried vertical U-tube ground-coupled heat pump in cooling operation .The paper mainly reports the ground temperature change after the heating operation of 50-meter-deep buried vertical U-tube ground-coupled heat pump and performance of system with several flow rates in summer , then the simulation of the performance by cylindrical heat source model.In the transition season ,the ground temperature gradually resumes, then goes to stabilization . According to the experimental data ,the temperature under 5 meters keeps constant; the temperature under 20 meters, 35 meters, 50 meters attach to 19.01 ℃,18.84℃, 19.24℃ respectively before the cooling operation. This resume of ground temperature attaches to 95%.To study on the law of ground cooling transfer ,the performance of system in 3#well is tested when the flow of rate is only 6451/h;several different flow rates of U-tube such as 6451/h, 7001/h, 7601/h are applied for l#well. The flow rate of 7601/h is preferable by comparison of coefficient of heat exchange and average quantity of heat per meter. In the operation of the flow rate of 7601/h in 1# well ,the coefficient of heat exchange , average quantity of heat per meter and coefficient of performance are 6.40w/m℃. ,69.47w/m, 3.44w/w.According to the analysis of the testing results , the effects of thermal short-circuiting between two legs of the U-Tube become more serious with the flow rate increasing.Based on the theories and experiments about GSHP, the cylindrical heat source model has been developed for the simulation of heat transfer over a vertical U-tube ground heat exchanger when the flow rate is changeable. The simulation shows that the maximal temperature error of entering and exiting water is 6.33%.The predicted data calculated by the model agree reasonably well with the experimental data.The model produces the average temperature average entering temperature average exiting temperature of the flow in buried pipe. At last the short-circuiting of system is analyzed.