# Transcritical R744 Supermarket Refrigeration System Integrated with a Heat-Driven Ejector Chiller
## 4 Conclusions  
The performance of a novel R744 refrigeration system coupled to a R717-based heat-driven multi-ejector chiller (HEC) was assessed for possible use in supermarkets. The energy-saving potential of the novel system at various warm and hot climatic locations was compared with several baseline systems, including an R744 refrigeration system coupled to R718- and R600a-based HECs, an R744 refrigeration system equipped with parallel compression (PC), and a standard R744 booster system (CB). The performance of the investigated systems was also evaluated at the optimal operating conditions of the PC and CB systems to determine the suitability of the existing high-pressure controllers, as developing a new set of controllers is expected to increase the investment cost. The economic aspect of the investigated systems was also assessed in terms of the additional investment required for the procurement of the HEC unit, providing better insight into this novel subcooling technology. The following conclusions were obtained from the study:  
* The integration of an R717-based HEC was found to improve the COP of the R744 refrigeration system by 3.7% at 27 \({}^{\circ}\)C to 12.1% at 45 \({}^{\circ}\)C compared to the R718-based HEC, and 1.6% at 27 \({}^{\circ}\)C to 7.6% at 45 \({}^{\circ}\)C compared to the R600a-based HEC unit;
* The R718-based HEC was found to be effective at outdoor air temperatures above 30 \({}^{\circ}\)C, while the R717 system could be operated beyond 24 \({}^{\circ}\)C. This tended to reduce the operational range of the R718 system;
* Even with eight ejectors, the cooling capacities of the R718- and R600a-based HECs were found to be lower by 67% and 42%, respectively, compared to the five-ejector integrated R717 system;
* The use of CB high pressure controllers with the proposed system was found to impose relatively less penalty in the system performance compared to the high pressure controllers of the PC system;
* The energy-saving potential of the R744 refrigeration system integrated with the R717-based HEC (6.2% to 9.4%) was found to be relatively higher compared to the R718 (0.7% to 2.8%) and R600a-based HECs (2.5% to 6.6%);
* Although the additional investment incurred due to the installation of the R718-based HEC was significantly lower compared to the R717 and R600a systems, the AIRT associated with the R600a-based HEC (2.3-4.8 years) was found to be relatively lower than the R717 (2.7-5.8 years) and R718 systems (2.7-6.4 years) in all the selected locations. * Even though the initial investment was high, R717 was found to be the best refrigerant for the HEC unit in terms of energy savings; however, necessary safety measures are required to be taken for use in sectors like supermarkets. R718 can definitely be an alternative to R717 in the future, once the technology associated with it becomes matured. Conceptualization, A.S., P.G. and V.K. ; methodology, A.S. and P.G. ; software, A.S.; validation, A.S.; formal analysis, A.S.; investigation, A.S.; writing--original draft preparation, A.S.; writing--review and editing, A.S., P.G., V.K. and M.S.D. ; visualization, A.S.; supervision, P.G., V.K. and M.S.D. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. **Conflicts of Interest:** Author [PERSON] was employed by the company Danfoss A/S. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. **Nomenclature**