Comparative thermodynamic evaluation of R290 for air-conditioning and commercial refrigeration applications in tropical climates

The transition to low-global warming potential (GWP) refrigerants for tropical applications requires a comprehensive understanding of system performance under extreme high-ambient conditions, which remain insufficiently addressed in existing literature. Most prior studies evaluate refrigerant performance at moderate ambient temperatures (≤ 40 °C) or rely on single-parameter metrics such as coefficient of performance (COP), which fail to capture the combined degradation in efficiency and cooling capacity under severe thermal stress. This study presents a thermodynamic evaluation of R290 (propane) as a low-GWP refrigerant for air-conditioning (AC) and commercial refrigeration (CR) systems under Indian climatic conditions, including extreme ambient temperatures up to 50 °C. A steady-state vapor compression cycle model is developed using CoolProp-based thermophysical properties, incorporating key assumptions such as fixed compressor speed (4000 RPM), constant isentropic efficiency (0.75), and standardized superheat and subcooling conditions. Performance is compared against R32 and R134a under both standard and high-ambient operating conditions on an equal cooling capacity basis. Results indicate that while R290 demonstrates competitive performance under standard conditions (COP ≈ 3.57 in AC mode), significant degradation occurs at high ambient temperatures, with COP reductions of approximately 25–30% in AC and higher in CR applications. The degradation is primarily driven by increased pressure ratio, elevated discharge temperature, reduced refrigerating effect, and enhanced flash gas formation due to limited subcooling. To address the limitations of conventional performance metrics, a novel Performance Degradation Index (PDI) is introduced, integrating both COP reduction and cooling capacity loss into a unified framework. The PDI analysis reveals that R290 exhibits moderate degradation compared to R32 and R134a, with consistent ranking across different weighting scenarios, demonstrating robustness of the proposed metric. The findings highlight that although R290 offers favourable thermodynamic characteristics and lower thermal stress, its performance under high-ambient conditions is governed by complex interactions between pressure ratio, volumetric efficiency, and phase-change behaviour. The study provides a comprehensive framework for evaluating refrigerant performance under extreme climates and offers insights into compressor and system design considerations for reliable deployment of low-GWP refrigerants in tropical regions. Graphical Abstract