HFO in the Future Scenario of Commercial Refrigeration Systems: Energy Performance and Environmental Impact

This PhD thesis contributes to understanding how low-GWP refrigeration systems perform under real supermarket conditions and highlights the importance of specific design choices. The findings emphasize the trade-offs between energy efficiency, refrigerant, and environmental risk. The integration of field data, dynamic modeling, and environmental assessment provides a practical framework to support future refrigeration technology decisions in a world that is decarbonizing. The first part of the study investigates two low-GWP operational supermarket refrigeration systems installed in northern Italy, with more than 40 million data points measured in one-minute intervals, collected over a full year: a transcritical CO2 system and a cascade system using R1234ze(E) and CO2 as refrigerants. Each represents a different approach to mitigate climate impacts, balance system complexity, ambient sensitivity, and refrigerant properties. Both systems are integrated with heat recovery functionality. The second part of the study focuses on evaluating heat recovery from the system analyzed in the first part, enabling a detailed assessment of its seasonal performance and energy consumption. Particular attention is given to understanding the role of integrated heat recovery, which can substantially enhance overall system efficiency during colder periods, as well as to examining how system performance differs when operating in heat recovery mode. A thermodynamic model incorporating floating condensation pressure control was developed in MATLAB with REFPROP, offering valuable insights into system behavior and optimization potential. In addition, the performance of integrated heat pumps and air-conditioning systems is evaluated. The study demonstrates that the CO2 system equipped with a parallel compressor is a promising solution for the mild to warm climate of northern Italy, as its average annual coefficient of performance in floating condensation mode surpasses that of the cascade system. However, the HFO/CO2 cascade system presents a valuable opportunity for continuous heat recovery, offering lower complexity and higher global efficiency, avoiding the deterioration of efficiency observed in transcritical operation of the CO2 system. The results of this research are presented and discussed in detail in Chapters 1 and 2, and have been published in two peer-reviewed journal articles (Part I and Part II) as part of this PhD work. In addition, a direct expansion system using R455A is examined, focusing on its performance in mild and warm climates and potential improvements. The results show that, in theory, the direct expansion R455A system outperforms the CO2 system without a parallel compressor at an ambient temperature of 10 °C. Under specific heat recovery conditions, R455A can achieve a higher global coefficient of performance. However, CO2 transcritical systems with a wide temperature glide enable an effective thermal match with water or air streams, enhancing their potential for heat recovery in different scenarios. Properly designed CO2 transcritical systems with heat recovery can supplement or replace conventional boilers, providing hot water or process heat. This option is less feasible for HFO systems. Following field analysis, a life cycle assessment was performed to evaluate environmental performance beyond energy use, including refrigerant leakage, manufacturing, and end-of-life impacts. The results show that both CO2 and cascade systems using very low-GWP refrigerants deliver comparable performance. However, the use of glycol-water loops in the cascade system and associated toxicity and emissions make the CO2 system a more favorable choice. In contrast, the R455A system, though simpler in design, leads to significantly higher direct emissions during operation due to its higher GWP.