Thermal comfort and airflow evaluation of an Automated Rapid Transit (ART) using Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD)

The optimization of airflow and thermal comfort in public transportation is essential for improving passenger satisfaction and energy efficiency, particularly in hot and humid climates such as Malaysia. This study investigates airflow distribution and passenger thermal comfort within an Automated Rapid Transit (ART) middle carriage using Computational Fluid Dynamics (CFD) integrated with Fanger’s Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indices. The ART carriage was modelled in SolidWorks to replicate the actual geometry, and field measurements were conducted to validate the CFD model, resulting in an average error of 7.01%, which confirms the reliability of the numerical approach. Airflow and temperature distributions were analyzed under three passenger-loading conditions: AW1 (16 seated passengers), AW2 (16 seated and 58 standing passengers), and AW3 (16 seated and 74 standing passengers). Simulations were performed at inlet air velocities of 1.6, 2.9, and 3.2 m/s and inlet air temperatures of 14.7°C and 8.7°C. The results indicate that increasing passenger density leads to higher cabin temperatures and reduced airflow uniformity. Breathing-zone air velocities increased from approximately 0.23 m/s at 1.6 m/s to about 0.60 m/s at 3.2 m/s, raising the risk of draft discomfort. In high-density conditions, central cabin regions were up to 5.7°C warmer than side areas due to metabolic heat accumulation. Thermal comfort evaluation using PMV and PPD indices, supported by selected passenger analysis via the CBE Thermal Comfort Tool, identified AW2 at an inlet velocity of 2.9 m/s and temperature of 8.7°C as the optimal operating condition. Under this condition, most passengers experienced near-neutral thermal sensation (PMV = −0.67 to +0.47) with low dissatisfaction levels (PPD = 6–14%). In contrast, AW3 exhibited severe thermal non-uniformity, with PMV values ranging from −3.6 to +4.3 and PPD reaching 96–100%. These findings provide validated numerical insights for optimizing ART HVAC design and enhancing passenger-oriented thermal comfort in tropical public transport systems.