Evaluation of the carbon footprint of HFC and natural refrigerant transport refrigeration units from a life-cycle perspective

In recent years, the temperature-controlled transport sector has experienced a substantial growth, and this trend is expected to accelerate in the coming years. However, as the sector expands, it becomes imperative to address and mitigate the carbon footprint of transport refrigeration systems. The carbon footprint of a refrigeration system comprises both direct emissions from refrigerant leakage and indirect emissions derived from energy consumption. In this study, dynamic numerical simulations are used to evaluate the annual performance of a conventional HFC (R134a) transport refrigeration unit and of a newly developed natural refrigerant (R744) one employed in a multi-drop delivery mission in urban environment. Additionally, a simplified life cycle approach is used to compare the carbon footprint of these cooling units across various stages of the system supply chain, including refrigerant production and recycling, unit manufacturing, operation and disposal. Results show that the R744 unit presents significantly higher COP for high ambient temperatures, while its performance is degraded for low ambient temperatures due to low duty cycle. On annual basis, the R744 unit COP is 27.5 % higher than the R134a one. However, the increased weight of the R744 unit results in significantly higher emissions associated with fuel consumption required to transport the unit weight, leading to slightly higher fuel related emissions (+9.3 %) for the R744 unit. Nevertheless, the high GWP of R134a contributes to substantial direct emissions due to refrigerant leakages, resulting in an overall 31.9 % reduction in the lifetime CO2 equivalent emissions for the R744 unit when considering the total emissions.