Comprehensive assessment of energy and environmental performance of CO2 heat pump system with dual indoor units for electric vehicles

초록

Recently, regulatory restrictions on per- and polyfluoroalkyl substances accelerated the transition toward environmentally friendly refrigerants. Among the available alternatives, CO2 stood out due to its low global warming potential and zero ozone depletion potential. Although recent research increasingly focused on integrating CO2 into automotive systems, comparative studies with widely used R-1234yf systems remained limited. Furthermore, the relatively lower cooling performance of CO2 remained a significant challenge. This study addressed these gaps by implementing a dual-indoor-unit configuration to enhance the performance of CO2 systems through experimental and simulation approaches. The system was evaluated under steady-state and transient conditions across various driving cycles and was compared with conventional R-1234yf heat pump systems. Key findings showed that, for the same power consumption, the dual-indoor-unit CO2 system achieved a slightly higher cooling capacity than the R-1234yf system, whereas the single-indoor-unit CO2 system provided only 77% of the R-1234yf system's cooling capacity. In heating mode, the dual-indoor-unit CO2 system delivered approximately 2.3 times the heating capacity of the R-1234yf system. In driving cycle condition, the dual-indoorunit CO2 system matched the cooling performance of the R-1234yf system while reducing the heating time from 600 to 180 s. Energy efficiency improved by 29.0% in cooling mode and by 18.5% in heating mode, consequently extending the driving range. Furthermore, the environmental evaluation indicated a 20.1% reduction in lifecycle carbon dioxide emissions during cooling operation. These results supported the viability of the dualindoor-unit CO2 heat pump system as a sustainable solution for electric vehicles.

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