Vertical Pipe Heat Exchanger Performance

It is a trend of world development that renewable energy is gradually to replace conventional energy, and ground source heat pump (GSHP) technology, which meets buildings needs of air-conditioning, heating etc. by utilizing shallow geothermal resource, is an important means of the use of renewable energy; meanwhile, developing GSHP is also the requirement of China's energy construction adjustment. Vertical U-tube heat exchanger have been widely used because of many notable advantages it has, such as fewer area requirement, extensive application, running steadily, high performance, lower cost on system maintenance etc. Vertical heat exchanger is mainly divided into single U-tube heat exchanger and double U-tube heat exchanger.This thesis aims to study the heat transfer of GSHP vertical ground heat exchangers. It experiments on the summer-and-winter condition at continuously operation mode focused on a set of GSHP system in Changsha, Hunan Province, which contains a real-time collection of data including the inlet (outlet) soil water temperature of U-tubes, flow rate in pipes, soil temperature, and so on. The analysis of these data emphasizes the comparison between the inlet (outlet) temperature differences of the heat exchangers in buried pipes as one, and the heat transfer of ground heat exchanger for unit depth as the other, both of which are conducted under different conditions, buried forms, and buried depths. The research comes to a conclusion that in both summer condition and winter condition, double U-pipe exceeds single U-pipe in the heat transfer of ground heat exchanger for unit depth by 25%-30%.Then, numerical models of single U-tube borehole and double U-tube borehole heat exchanger for ground-coupled heat pump was constructed based on energy balances and law of conservation of mass. energy transferred between the fluid and the tube wall and heat conduction in the ground was simulated, the temperature of fluid in outlet of bore hole heat exchanger and variation of ground temperature around the borehole were investigated;Comparison of double U-tube heat exchanger with single U-tube heat exchanger operating characteristics were taken from heat exchanger exit temperature, Heat capacity of borehole, the impact on soil temperature and other aspects。It can be concluded that the double U-tube borehole heat exchanger offered a better performance than single U-tube borehole heat exchanger. The results show that in the same system, and the same condition, double U-tube exceeds single U-tube in the heat transfer of ground heat exchanger for unit depth by 30%.These models developed in this paper can be easily applied in practical projects, and the conclusion is of significance for proper design and energy consumption forecast of GSHP system.