Experimental Study Of Effects Of Compressor Frequency And Regenerative Heat On The Performance Of The Transcritical CO₂ Cycle Heat Pump

The use of CFCs and HCFCs refrigerants is subject to many restrictions with the completion of the Kigali Amendment.As a natural working fluid,CO₂ is safe and environmentally friendly,and has good thermodynamic properties.Compared with other alternative refrigerants,CO₂ is regarded as“the most promising refrigerant in the 21st century”.Due to the serious throttling loss and high irreversibility of the traditional transcritical CO₂ cycle,in order to improve the circulation efficiency,the regenerator is introduced into the transcritical CO₂ cycle heat pump in this paper.And an evaluation index-the regenerative heating rate is proposed to evaluate the influence of regenerative heat on the heat pump performance,whose variation characteristics with the regenerative heating rate under different working conditions are investigated.Furthermore,the effect of compressor frequency on the heat pump performance is also conducted in this paper.The research results can provide a reference for the rational design and operation of regenerator in the transcritical CO₂ cycle heat pump.The main contents are as follows:（1）The performance of transcritical CO₂ cycle heat pump with or without regenerator is analyzed.It is found that the use of regenerator can improve the system COP_has the system runs at lower discharge pressures,under which the use of regenerator makes the system obtain higher COP_h.（2）Discharge pressure varies from 7.4 MPa to 11 MPa,and ambient temperature is kept at 15°C,as the heat pump is operated at different compressor frequencies,the effect of compressor frequency on the performance of the heat pumpare studied experimentally,including the heating performance,the compressor performance and energy efficiency of the system.The heating performance includes gas cooler outlet temperature,the system heating capacity and water outlet temperature;the compressor performance:compression pressure ratio,suction pressure,compression specific work,discharge temperature,isentropic efficiency,volumetric efficiency and mechanical efficiency;energy efficiencyof the system:COP_h.（3）The variation trends of compressor suction temperature,compression ratio,the system heating capacity,water outlet temperature and the system COP_h with regenerativeheating rate under different working conditions areinvestigated experimentally.According to different design goals,the suitable design regenerative heating rateis determined,respectively.The research shows that underdifferent compressor frequencies and gas cooler inlet temperatures,if the systemmaximum COP_his regarded as the design goal,the design regenerative heating rate should be about 12.7%¹7.4%;if the system highest water outlet temperature is regarded as the design goal,the design regenerative heating rate should be about 3.2%⁹.9%.Therefore,the system can provide higher water outlet temperature operated at the lower regenerative heating rate,and the system can obtain larger COP_hoperated at the higher regenerative heating rate.