Optimization And Analysis Of Dual-source Carbon Dioxide Heat Pump System With Parallel Compressor

Nowadays,with the in-depth development of industrial economy,environmental problems have become increasingly prominent and energy shortages have been aggravated.With the improvement of living standards,people’s requirements for comfort in life are also getting higher and higher.Air source heat pump(ASHP)has been widely studied and applied in the family,industry and commerce because of its high energy utilization,safety,environmental protection and convenient use.However,air source heat pump has its limitations,among which poor adaptability to cold environment is an important factor hindering its further development.In the north of China where the temperature is low in winter,when the hot water temperature is high,the heating efficiency of air source heat pump will drop sharply,and it will lead to the reduction of the efficiency and the shortening of compressor life caused by the high pressure ratio of compressor.Therefore,conventional air source heat pump systems are difficult to meet the needs of large quantities of high temperature hot water in commerce.Compared with air source heat pumps,ground source heat pumps are less affected by ambient temperature because of their characteristics of absorbing deep geothermal energy and stable operation.However,the installation and maintenance of ground source heat pump system is difficult.When the demand for hot water is large,its installation difficulty and installation cost are both its drawbacks.In this paper,an advanced dual-source CO2 two-stage parallel compression hot water heat pump system(DEPC)was proposed by combining a dual-source system with a two-stage parallel compression system.Based on the second law of thermodynamics,the thermodynamic model of each system was established,and then the mathematical model and calculation were carried out in MATLAB to conduct in-depth simulation and analysis of the system.The results show that:1)The optimal state point of the system is found with COP as the main standard.When the outlet pressure of the compressor is 86 bar and the middle throttle coefficient is 1.25,COP of the optimal state point of the system is 3.85.2)The addition of regenerator can improve the high temperature hot water preparation ability of the system;The optimization of intermediate throttling pressure can improve system performance;The parallel compressor can effectively share the operating load of the high-pressure compressor and improve the rationality and stability of the system;The use of double heat sources and the system structure of two-stage compression can be achieved.COP of the system can be increased with significant improvement,up to 45%.3)With the increase of ambient temperature,the COP of single air source system and dual-source system are increased,but the performance advantage of dual-source system is gradually reduced.4)The system exergy efficiency at the optimal state point is 31.54%.The throttle valve at the high-pressure side of the system and the high-pressure compressor are the two most exergy loss components in the system,which have a large optimization space.From the view of the first law of thermodynamics and the second law of thermodynamics,this paper studied the dual-source carbon dioxide heat pump system,proposed a parallel compression two-stage R744 system and performed in-depth parameter analysis and exergy analysis.It is of guiding significance for developing energy efficient and environmental-friendly heat pump systems.