Energy-exergy investigation of electric vehicle air-conditioning systems using R1234yf refrigerant and synthetic compressor lubricants

Electric vehicle air-conditioning (EV-AAC) systems are among the most energy-intensive auxiliary loads, and refrigerant–lubricant interactions critically influence overall efficiency. Despite their importance, the compatibility of synthetic lubricants with the demanding thermal and electrical environment of EV-AAC systems remains insufficiently established. This study experimentally investigates the thermodynamic and exergetic performance of a compact R1234yf-based EV-AAC system lubricated with polyol ester (POE), polyvinyl ether (PVE), and polyalphaolefin (PAO), tested across varied compressor speeds and refrigerant charges. A custom-built EV-AAC test rig charged with R1234yf and lubricated with POE, PVE, and PAO was employed to assess thermodynamic and exergetic performance. Cooling capacity was measured using water-side calorimetry in accordance with ASHRAE 41.9-2000, with compressor speeds ranging from 2000 to 5000 rpm. System temperatures, pressures, and mass flow rates were monitored using calibrated sensors. Compared with POE, PVE and PAO reduced the average COP by 5.1% and 17.8%, respectively, while increasing compressor power by 45.9% and 53.3%. Exergy analysis also showed that POE delivered the highest second-law efficiency and the lowest EDR, whereas PAO exhibited the greatest compressor exergy destruction (58.50–61.26% of total exergy destruction), identifying the compressor as the dominant source of thermodynamic irreversibility. These findings provide valuable thermodynamic insights into lubricant selection for R1234yf-based EV-AAC systems, highlighting the potential of nanoparticle-enhanced lubricants to deliver further performance gains.