The Energy Analysis Of Carbon Dioxide Two-stage Compression Refrigeration Heat Pump Cycle For Simultaneous Cooling And Heating

In this paper,a two-stage carbon dioxide two-stage compression and cooling heat pump cycle with simultaneous cooling and heating is proposed,and its working principle,composition,operation mode and control scheme are described in detail as air conditioning heat pump water heater.The system,using carbon dioxide as working fluid,can simultaneously produce air conditioning chilled water and hot water in the summer conditions and overcome the low efficiency and low utilization of the existing condensing heat recovery air conditioning system at the same time.In order to further explore its energy saving potential,improve the system and optimize the system operation plan,the author analyzes the efficiency of the system under different refrigerant mass flow rate,different intermediate pressure and different discharge pressures of the high-pressure compressor.The results show that when the outlet pressure of the high pressure compressor varies from 8.5MPa to 12 MPa,the exergy efficiency of the system decreases with the increase of the flow coefficient.When the pressure exceeds 10 MPa,the decrease will be more obvious,and the decline rate of the exergy efficiency of the system will suddenly drop at the flow coefficient of 0.3.When the system middle pressure changes from 5MPa ~ 7MPa,the exergy efficiency of the system increases at first and then decreases with the rising of the outlet pressure of the high pressure compressor,and the maximum exergy efficiency of the system is obtained when the outlet pressure of the high pressure compressor reaches 9MPa.When the flow coefficient changes from 0 to 1,the exergy efficiency of the system increases with the rising of the intermediate pressure,and the larger the flow coefficient is,the higher increasing rate the system exergy efficiency will have when the intermediate pressure changes.Although the system can adjust the recovery of heat,as the recovery of heat increasing,the exergy efficiency of the system will be reduced.When the outlet pressure of the high-pressure compressor is increasing continuously,the water heater,displacing the first throttle valve,becomes the component of the largest exergy loss rate,and when the intermediate pressure is declining continuously,the second throttle valve rather than the first one becomes the component of the largest exergy loss rate.And the heat source side heat changer is the component with the lowest exergy efficiency at the rate of 57.3%,but the heat source heat exchanger only have a prominent impact when the heat of the system is greatly demanded.Therefore,the first throttle valve at low pressure,the water heater at high pressure and the heat source heat exchanger are the main objects of the whole system improvement.It is also found that as the pressure and the mass flow coefficient of the refrigerant changes,the exergy efficiency rate and loss rate of the heat source heat exchanger alters little while the exergy efficiency of water heater has a great decline from 94.7% to 62.0%with the increasing pressure.