Experimental Study On Circulating Single Stage Compressed Carbon Dioxide Heat Pump Water Heater

Due to the long-term use of chlorofluorocarbons as refrigerants in heat pump systems,a series of environmental problems such as the greenhouse effect and the destruction of the ozone layer have emerged.In order to protect the atmospheric environment in which we depend,the refrigeration of chlorofluorocarbons has been reduced and limited.The use of working fluids,therefore,it is extremely urgent to find environmentally friendly refrigerants to replace the refrigerants of chlorofluorocarbons.The circulating single-stage compressed air source carbon dioxide heat pump hot water studied in this paper uses carbon dioxide as a refrigerant,which is cheap and easy to obtain,energy-saving and environmentally friendly,and is in line with China’s national policy of energy saving,energy saving and emission reduction.This topic is based on the instant single-stage compression of carbon dioxide,mainly designed for the outdoor environment temperature is too low,the air cooler water temperature does not meet the user’s needs.In order to understand the operating characteristics of the circulating single-stage compressed air source carbon dioxide heat pump system,a circulating single-stage compressed carbon dioxide heat pump water heater test bench was designed and built.Firstly,the experiment of the optimal charging amount of carbon dioxide refrigerant was carried out to determine the optimal carbon dioxide charging amount of the experimental system.Based on the changes of parameters such as outdoor ambient temperature and circulating water flow,the system performance and the water tank temperature were divided.The effects of the layers were studied experimentally.The experimental research shows that:(1)Under the condition that the water flow rate of the air cooler is 2L/min,the temperature is 10℃,and the other parameters remain unchanged,the optimal charging amount of the carbon dioxide refrigerant in the experimental system is tested.The experiment finds: As the charge of carbon dioxide refrigerant increases,the suction,exhaust pressure and power consumption of the compressor gradually increase;while the intake and exhaust temperatures of the compressor gradually decrease;the system heat and COP with carbon dioxide refrigerant The increase of the charge amount first increases and then decreases.The optimal charge amount of the experimental system is determined by comprehensive consideration and analysis,4.0kg;(2)The initial water temperature of the water tank is 10℃,and the ambient temperature is-5℃.The remaining parameters remain unchanged.The operation performance of the system is experimentally analyzed when the inflow of air cooler is 1.5L/min,2.0L/min and 2.5L/min respectively.The experimental results show that the higher the inflow rate of air cooler,the lower the outlet temperature of air cooler,the higher the COP and heating capacity of the system;the running time the smaller the circulating water flow,the more obvious the temperature stratification of the water tank.(3)The initial water temperature of the water tank is 10℃,and the inflow rate of the air cooler is 2 L/min,while the other parameters remain unchanged.The operation performance of the system at ambient temperatures of-5℃,5℃ and 15℃ was experimentally analyzed.The experimental results show that the higher the ambient temperature is,the greater the heating capacity,COP,exhaust pressure and power consumption of the system;the higher the ambient temperature is,the more obvious the phenomenon of temperature stratification of the water tank is.When the temperature of 50 L water in the tank reaches 40℃,and the heating time is shortened.(4)When the initial water temperature of the water tank is 10℃,the inflow rate of the air cooler is 2L/min,the ambient temperature is 15℃,and the other parameters remain unchanged,the experiments are carried out before and after adding the separator.The results show that when the system runs for 2500 seconds,the inflow temperature of the air cooler decreases by 32%,the COP increases by 11.8%,the heat of the system increases by 8.5%,and the exhaust pressure of the compressor decreases by 6.4%.When the temperature of 31.4L water in the tank reaches 40℃,the heating time is shortened by 550 s.After modification,the system performance has been improved obviously.