Performance Improvement of Low-Temperature CO2/NH3 Cascade Refrigeration Systems through Subcooling Techniques: A Case Study in Indian Seafood Processing Application

Abstract Growing concern over the environmental impacts of synthetic refrigerants has intensified the need to reduce total carbon-equivalent emissions from refrigeration systems. Deep freezing is critical for preserving the seafood cold chain. India, the world's third-largest fish producer, contributed around 8% of global fish output in 2023–2024, with production reaching 17.5 million metric tons, an annual growth of 9.6%. This growth underscores the urgent need for energy-efficient cold chain solutions to enhance sustainability and global competitiveness. This study evaluates three advanced subcooling-integrated dual-evaporator carbon dioxide–ammonia cascade refrigeration systems against a conventional system without subcooling. Configurations include: (1) a system with mechanical subcooling in both low-temperature and high-temperature circuits, (2) a system with economizer-based subcooling in the low-temperature circuit and mechanical subcooling in the high-temperature circuit, and (3) a system with economizer-based subcooling in both circuits. Performance indicators include annual energy consumption, total equivalent warming impact, and life-cycle cost. For low-temperature subcooling of 1–10K, the system with economizer subcooling in both circuits achieves the highest reduction in compressor power (10.5–12.2%) and coefficient of performance improvement (11.8–14%). The combined economizer and mechanical subcooling show moderate gains, while fully DMS system shows the lowest improvement. The fully economizer-based subcooling system also achieves the highest seasonal energy efficiency and lowest life-cycle cost, making it the most energy-efficient and cost-effective solution for high-ambient seafood cold chain applications.