Application of Transcritical CO₂ System with Ejector in Large Cold Store

Large cold storage systems play a significant role in economic development with substantial energy consumption and environmental impacts. To promote the green, low-carbon, and efficient development of cold storage, this study mainly focuses on refrigerant substitution, refrigeration system optimization, and the application of transcritical CO₂ systems with ejectors in large cold storage systems. The performance and energy consumption characteristics of different refrigeration systems were compared through a comprehensive annual hourly energy consumption analysis based on the cold storage demands at different temperatures and under various climatic conditions. The results show that the COPs of a transcritical CO₂ system integrated with specifically optimized ejectors are higher than that of the R507A system in all four cities for low-temperature (-32 ℃), medium-temperature (-8 ℃), and high-temperature (0 ℃) cold storages. However, it exhibited performance advantages over the R717 system only in cold climate zones, with the highest system COPs of 2.45, 4.86, and 5.98 for low, medium, and high-temperature cold storages, respectively. Considering the system′s annual energy consumption, the application of CO₂ transcritical systems in low, medium, and high-temperature cold storages in Beijing achieved energy savings of 7.9%, 10.1%, and 10.5%, respectively, compared to the R507A system. The energy savings of the R717 system were slightly higher than that of the CO₂ system in low-temperature cold storage, but the CO₂ system had more obvious advantages in medium-and high-temperature cold storage. The energy consumption of the CO₂ transcritical system also varied across climate zones. In the cold climate zone, the energy savings reached 9.3%, outperforming the R717 system, while in the hot climate zone, its energy savings dropped to 2.8%, slightly lower than that of R717. With the appropriate selection of temperature range and climate zone, the overall operational efficiency and energy-saving performance of the transcritical CO₂ system can surpass those of the R717 system. This study conducted a comprehensive analysis of the operational performance and energy consumption distribution characteristics of the CO₂ system and highlighted its applicability in different scenarios, providing important references for promoting and applying the system, which is crucial for achieving dual carbon goals.