Energy, exergy, and environmental impact assessment of CO2-based booster refrigeration systems for tropical and subtropical climate zones

• CO 2 booster and cascade systems assessed across tropical and subtropical climates. • First CO 2 refrigeration assessment covering four major Colombian cities. • BS-E excels in cool-moderate climates; BS-C-E performs best in hot regions. • BS-E and BS-C-E minimise TEWI; R404A shows the highest impact. • System suitability varies strongly with climate, shaping efficiency and emissions. This study presents the energy, exergy, and environmental performance evaluation of five CO 2 -based refrigeration configurations, namely a conventional booster (BS), booster with parallel compression (BS-PC), booster with ejector (BS-E), NH 3 /CO 2 cascade booster (BS-C), and ejector-assisted cascade booster (BS-C-E), together with the conventional R404A systems, under high-altitude, tropical, and hot-humid climatic conditions representative of four major Colombian cities (Bogotá, Medellín, Cali, and Barranquilla). Results show that for ambient temperatures below 26 °C, ejector-assisted booster systems deliver the highest efficiency, with the lowest annual energy consumption in Bogotá, Medellín, and Cali (411636 kWh/year, 442,218 kWh/year, and 486,673 kWh/year, respectively), corresponding to energy savings of approximately 6.8–10.2% relative to the BS. At higher ambient temperatures, hot-humid climates, such as Barranquilla, the BS-C-E configuration provided the lowest energy consumption (492852 kWh/year), achieving up to 12.7% annual energy savings compared with BS. Exergy analysis reveals that gas coolers dominate irreversibilities in booster systems, whereas cascade configurations exhibit a more balanced exergy destruction distribution. Environmental assessment based on highlights a critical energy–environment trade-off. Although the R404A reference system shows lower energy consumption, the direct TEWI associated with R404A remains more than three orders of magnitude higher than that of the CO 2 -based systems, whereas for all CO 2 configurations direct emissions remain negligible and total TEWI is governed almost entirely by indirect emissions related to electricity consumption. Results show that climate-specific system selection is essential, balancing efficiency gains against system complexity, and environmental impact, and strongly supports the transition away from high-GWP refrigerants toward CO 2 -based technologies.