Heat Transfer Performance And System Dynamic Characteristics Of Underwater Pipe In Closed-Loop Surface Water Source Heat Pump System

Surface water source heat pump system has attracted increasing attention recently in the air-conditioning projects near the river or lake,which is the environmentally friendly and low cost technology in the field of building energy efficiency.There are many lakes besides the Yangtze River and its tributaries in Chongqing,and the development of surface water source heat pump technology significantly benefits from the rich water resources.In this study,an air conditioning system of Chongqing residential building is taken as the object,and the heat transfer performance and system dynamic characteristics of underwater exchanger pipe for closed-loop surface water source heat pump is analyzed by experiment and numerical simulation.Firstly,an experimental device of underwater spiral heat exchanger pipes was set up for analyzing the effects of flow rate and inlet temperature on heat transfer performance.The average heat transfer of fifteen cases were studied in which the flow rate and inlet temperature varied in 0.8、1.0、1.2 m³·h_-1 and 16、17、18、19、20℃,respectively.The experimental results showed that the average heat transfer per pipe was 49 W·m-1 when the inlet temperature,heat transfer temperature difference and the flow rate was 20 ℃,8 ℃,and 1.2 m³·h_-1,respectively.With increasing flow rate,heat transfer per length was increased while temperature difference between inlet and outlet was decreased.With increasing inlet temperature,the heat transfer per length and temperature difference between inlet and outlet were both increased.Secondly,the numerical simulation model of underwater heat exchanger pipe with length of 100 m was developed by finite volume method to analyze the heat transfer performance of the pipe.The study on heat transfer along the pipe length showed that the single pipe heat exchange of every 10 m section was reduced when flow was closer to the outlet side with extending length of pipe.And the heat transfer of different pipe sections decreased with increasing flow rate,and the decrement range of that was reduced.It was also found that the length of single heat transfer pipe can be larger than 100 m to increase the heat exchange when the load fluctuation was small during the operation of heat pump;while the length of the single pipe should be reduced,and the number of groups should be increased when the load fluctuated for a long time.The study on variation of water temperature in the whole heat pump system region showed that temperature increase was less than 1 ℃,so the system would not cause the thermal pollution.Finally,DeST building energy consumption model was established using TRNSYS to build water source heat pump system.Selecting parameters of heat pump,matching rated cooling / heating capacity,determining the length of a single coil and coil number,and calculating best flow of source side were firstly done for the residential buildings.It showed from 8760 h dynamic simulation of heat pump that COP varied hourly in one year which affected by water temperature.It was also found that COP was about 6 in cooling mode when different system configuration scheme of heat pump units were used;COP was about 3 when two units operated in heating mode,and its COP was nearly increased 30% compared with that of one unit.The investment and environmental benefits of the closed-loop water source heat pump system were analyzed and compared with those of traditional equipment and ground source heat pump.