Range enhancement of electric vehicles with R744 thermal system under cold conditions

The application of R744 (CO₂) refrigerant in electric vehicle (EV) thermal management systems (TMSs) has attracted significant attention due to its high efficiency and environmental advantages. Under extreme cold conditions, ensuring passenger thermal comfort while maximizing driving range is critical for TMS. Aiming to address the challenges of comprehensive performance, this research investigates an R744-based TMS with serial heat recovery, specifically designed to enhance performance under low temperatures. The key operational parameters which significantly influence system performance were first identified and quantitatively evaluated. Experimental results demonstrate that the heat recovery mechanism enhances system performance, achieving a 21.9 % increase in driving range at −20 °C, while improving heating capacity under extreme cold conditions. The research also highlights the diminishing marginal benefits of excessive heat recovery, emphasizing the need for parameter optimization to balance performance gains and energy efficiency. A 3D cabin thermal model and Predicted Mean Vote based evaluation were used to assess thermal comfort. The findings confirm that the system can rapidly achieve and maintain passenger comfort, even at ambient temperatures as low as −30 °C. The study provides a practical framework for system design, offering theoretical insights for extending driving range and enhancing passenger comfort in EVs.