<p>The present investigation aims to identify the most suitable natural refrigerant—carbon dioxide (CO₂), nitrous oxide (N₂O), or ethane (C₂H₆)—for use in dual systems typically required in dairy processing plants. A comprehensive thermodynamic analysis was conducted to evaluate component-wise irreversibility and to calculate the optimal gas cooler pressure for four key performance criteria: maximum coefficient of performance (COP), maximum milk flow rate per kilowatt of power input, maximum milk flow rate per kilowatt of exergy destruction, and minimum cost for a specified annual milk pasteurization load. A slight variation was observed in the optimal gas-cooler pressures across the different objective functions, providing practical guidance for selecting operating conditions. Among the systems analysed, the N₂O–expander configuration delivers the strongest overall performance, achieving the highest COP (5.58) and the largest specific milk flow rate (0.0488 kg/s/kW). In comparison, the CO₂ system shows higher exergy destruction rates, reflecting its relatively lower thermodynamic performances. The results also show that the C₂H₆ system with an expander significantly enhances performance, increasing the milk flow rate per unit exergy destruction rate by up to 30% and yielding the shortest payback period of 0.23 years. Furthermore, detailed economic and environmental assessments were conducted for all refrigerant–expansion device combinations. These assessments highlight the trade-offs between energy efficiency, cost-effectiveness, and sustainability, enabling the selection of optimal system configurations for dairy operations.</p> Graphical Abstract <p></p>