Research On The Air-injection Heat Pump Air-conditioning System

Traditional single-stage compression(SSC)heat pump air conditioning system in electric vehicle has poor performance in low temperature environments.A gas-injected compression(GIC)heat pump air conditioning system with an economizer can effectively overcome this problem,improve system heating capacity,and reduce compressor discharge temperature.Compared with the SSC heat pump system,the GIC heat pump system adds a gas-injected circuit with an economizer and adds a gas injection hole on the compressor,so the design and operation of SSC system are more complicated.The theoretical analysis of the GIC process in a scroll compressor with R134 a is carried out in this paper,and the performance parameter calculation program of SSC and GIC heat pump system is designed by using MATLAB/SIMULINK and REFPROP.The heating capacity of the two heat pump systems under different working conditions is compared and analyzed.The simulation results show that: under all simulated conditions,that is,the ambient temperature is-15? to 0?,the heating capacity,compressor power and heating coefficient of performance(COP)of the GIC system are higher than that of the SSC system,and the discharge temperature is lower than that of the SSC system.With the increase of the ambient temperature,the COP difference between the two systems gradually reduces.When the ambient temperature is 0?,the COP difference between the two systems is less than 5%.Therefore,the ambient temperature 0? can be regarded as the temperature switching point of the two heat pump systems.The simulation and experimental results show that the heating capacity,compressor power and COP of the two heat pump systems increase with the increase of ambient temperature.As the compressor speed increases with the decrease of ambient temperature,the discharge temperature increases with the decrease of ambient temperature.However,the GIC system can improve the heating performance,so compared with the SSC system,the heating performance of the GIC heat pump air conditioning system decreases slowly with the decrease of the ambient temperature.Under the condition of-15?,the heating capacity of the GIC system using R134 a is 25% higher than that of the SSC system,the heating COP is 14% higher than that of the SSC system,and the discharge temperature is not more than 100?,which can ensure the safe operation of the system.A computational fluid dynamic simulation of the gas-injected scroll compressor was performed.The flow field under different working conditions is analyzed.There are two working conditions: adjusting the compressor speed under the same discharge pressure and adjusting the discharge pressure under the same compressor speed.The pressure,temperature field and velocity distribution in the compression chamber keep the same at different discharge pressure and compressor speed,but the values all increase.At the same compressor speed,with the increase of discharge pressure,the compressor displacement increases;at the same discharge pressure,with the increase of compressor speed,the compressor displacement decreases.