• • Increasing top exhaust airflow rate reduces average compartment temperature, improving energy utilization coefficient in summer but degrading it in winter; this seasonal divergence mandates mode switching to avoid 10–15% heating energy penalties in cold climates.
• • Combined top and bottom exhaust improves air velocity and temperature difference indices, with DR < 10% and PD < 3% satisfying ISO 7730 Class A; this ensures passenger thermal comfort without additional HVAC load, critical for high-occupancy train cabins.
• • Higher top exhaust airflow decreases average pollutant concentration but increases longitudinal penetration distance; this trade-off implies that infection control strategies must balance local dilution against global spread, particularly for airborne pathogens with high infectivity.
• • Optimal operational recommendations: full top exhaust in summer, 50% coordinated exhaust in winter; this mode-switching capability requires no end-pipe layout changes, enabling retrofits with zero structural modification and minimal downtime.