# Transcritical R744 Supermarket Refrigeration System Integrated with a Heat-Driven Ejector Chiller
## 1 Introduction
However, adoption of the heat-driven ejector system was reported to increase the installation cost by 1.5 times over the standard R744 system. [PERSON] et al. [22] reported R1233 zd(E) to be a more suitable working fluid compared to R245 ca and R601b for the heat-driven ejector cycle. The integration of the heat-driven cycle was reported to improve the COP of the system by 32.7% over a standard single-stage R744 refrigeration system. A major issue with the configuration reported in [22] was the integration of a generator at the outlet of the low-stage compressor to extract heat. This is expected to limit the operating temperature of the generator, which would affect the system performance due to the low discharge temperature of R744. However, due to the limited operating conditions explored in [20; 21; 22], it was difficult to evaluate the suitability of the heat-driven units in locations experiencing higher ambient temperatures. Further, none of the above literature was dedicated to the usability of natural refrigerants for the HEC unit. Usage of synthetic refrigerants, including HFOs, is not desirable due to their adverse impact on the environment. Also, none of the studies were dedicated to R744 supermarket refrigeration systems, nor were ejector control strategies or field measurements involved. Apart from this, the concept of a multi-ejector in the HEC unit was not explored in these studies. Recently, an investigation of a heat-driven ejector cycle coupled to an R744 refrigeration system was reported by [PERSON] et al. [16] for use in supermarkets. Several environmentally friendly refrigerants were assessed, among which R717 was identified as the best working fluid for the HEC. The combined usage of a multi-ejectorrack in the heat-driven cycle and parallel compression in the R744 system was reported to enhance the COP from 4.2% to 23.9% and reduce the annual energy consumption from 2.1% to 9.5% over a standard R744 system in the investigated locations. However, it was reported that the adoption of this new technology would be difficult due to the complexity of its control strategy and intricate circuitry. In particular, developing new controllers for this new technology would be difficult for any manufacturer, as it would require large investments. Further, the use of R717 in a sector like supermarkets could be challenging due to local regulatory measures. Hence, the present work aims to evaluate the potential of this novel subcooling technology in addressing these challenges, focusing on its accessibility and affordability from a practical perspective. The present study focused on evaluating the potential of a novel R744 refrigeration system equipped with an R717-based heat-driven multi-ejector chiller (HEC) for possible use in supermarkets. The multi-ejector rack of the R717-based HEC consisted of five fixed-geometry ejectors [16]. The performance of the novel configuration was compared with several baselines in terms of COP and energy savings at various warm and hot climatic locations, including India (Chennai and Delhi), the Middle East (Riyadh), the U.S.A. (Phoenix, Tucson, and Las Vegas), and Thailand (Bangkok). Natural refrigerants like R718 and R600a were explored as potential alternatives to R717 for use in the HEC unit. The key performance parameters and the challenges associated with their usage were also addressed to gain better insight. The multi-ejector racks of the R718- and R600a-based HEC were equipped with six to eight fixed-geometry ejectors. Adoption of new technology is always challenging due to the complex nature of its circuitry, which gives rise to the need to develop a new set of controllers, which may increase the investment cost. To counteract this challenge, the performance of the proposed system was also assessed at the optimal operating conditions of a conventional R744 booster system (CB) and a parallel compression-based R744 system (PC).