Thermal performance enhancement of R744 heat pump systems through configuration optimization in high-temperature environments

This study focuses on enhancing the refrigeration performance of the CO₂ heat pump system in high-temperature environments through an optimization of component configuration. Traditional CO₂ systems often experience a significant reduction in the coefficient of performance (COP) when operating in high-temperature conditions. Therefore, this paper proposes the integration of a water-cooled condenser (WGC) and improvements to the low-temperature radiator (LTR) to enhance the COP in these environments. A validated high-fidelity model is employed to evaluate three system configurations: the baseline system (OGC + upstream standard-size LTR), position-optimized configuration (OGC + downstream standard-size LTR + WGC), and size-optimized configuration (OGC + downstream enlarged-size LTR + WGC). The results show that the ultimate position and size-optimized configuration led to an 18 % increase in cooling capacity and a COP improvement of 0.19 at 43°C. Notably, these enhancements are most pronounced under low wind speeds with 1.5 m·s⁻¹ and high air volumes with 480 m³·h⁻¹. The study also reveals the limited impact of water flow rate while highlighting the significant effects of motor thermal load, with cooling capacity improving by 28.6 % at a 4000 W thermal load. Overall, the proposed hierarchical layout optimization of the WGC and LTR effectively enhances heat dissipation and improves system performance, offering a practical and environmentally friendly approach for electric vehicle CO₂ heat pump systems.