Steady-State and Dynamic Characteristics of Secondary Loop CO₂Thermal System for Electric Vehicles

With the rapid adoption of new energy vehicles (NEVs), effective thermal management has become a crucial factor for enhancing performance, safety, and efficiency. This study investigates the steady-state and dynamic characteristics of a secondary loop CO₂ (R744) thermal management system designed for electric vehicles. The secondary loop system presents several benefits, such as improved safety through reduced refrigerant leakage and enhanced integration capabilities with existing vehicle subsystems. However, these advantages often come at the cost of decreased thermodynamic efficiency compared to direct systems. Experimental evaluations were conducted to understand the effects of varying coolant flow rates, discharge pressure, and dynamic startup behaviors. Results indicate that while the indirect system generally shows a lower coefficient of performance (COP) than direct systems, optimization of key parameters like coolant flow rate and discharge pressure can significantly enhance performance. Specifically, optimizing the coolant flow rate resulted in a COP increase of up to 92.6% under certain conditions, while proper management of discharge pressure improved the heating capacity and system efficiency. Additionally, dynamic analysis of startup behaviors revealed the importance of effectively managing refrigerant distribution to achieve stable system operation and minimize energy losses. These findings provide valuable insights into the engineering feasibility and potential improvements of secondary loop systems. By focusing on the optimization of flow rate, pressure management, and startup control, this study supports the development of more sustainable and energy-efficient solutions for the thermal management of NEVs, ultimately contributing to the wider adoption of environmentally friendly transportation technologies.