From ventilation compliance to performance: experimental and cfd analysis of supply–exhaust design for airborne infection isolation rooms

Airborne infection isolation rooms (AIIRs) are critical for preventing healthcare-associated transmission of infectious aerosols. Current guidelines prescribe minimum air change rates (≥12 ACH) and negative pressure, yet compliance does not necessarily ensure effective contaminant removal from the patient breathing zone. This study advances a performance-based evaluation of AIIR ventilation by examining how terminal-level design parameters govern airflow directionality and contaminant capture. A full-scale negative-pressure isolation room (15.2 m², 36.8 m³) maintained at −20 Pa was investigated through integrated experiments and computational fluid dynamics (CFD). Dry-ice smoke served as a tracer to visualize airflow pathways and exhaust-air (EA) suction behavior, while validated CFD simulations resolved velocity fields and recirculation structures across five supply–exhaust (SA–EA) configurations investigated by CFD, with the baseline configuration additionally validated experimentally through tracer visualization and anemometric measurements. Anemometer measurements at the baseline EA grille reveal a strikingly non-uniform vertical suction profile, with the face velocity decaying from 1.63 m/s at 110 cm above the floor to 0 m/s at 30 cm, a mean vertical gradient of ∼2.04 (m/s) per m , attributable to a geometric mismatch between the effective EA opening (0.036 m²) and the substantially larger EA face area (0.792 m²) , an opening-to-face area ratio of only ≈ 1 : 22. This near-floor low-velocity region (<0.08 m/s) is below the buoyancy threshold of the CO2-laden tracer plume, which consequently accumulates and recirculates above the patient bed, generating stagnation regions that persist despite compliance with the prescribed pressure differential. Among the five cases evaluated, the optimized configuration (Case 5),combining coordinated SA jets, an air-curtain mechanism, and repositioning of EA3 to a wall clearance of 50 mm,delivered the best performance, raising the mean airflow velocity in the source zone to approximately 0.14–0.18 m/s and achieving near-complete suppression of stagnation zones, with airflow consistently directed toward the exhausts. These findings demonstrate that airflow structure and directional integrity in AIIRs are governed not only by ACH and pressure differential, but by the interaction of supply momentum, exhaust geometry, and spatial configuration,the fluid-mechanical prerequisites for effective contaminant control.