Scheduled Air Conditioning Operation Based on the Number of Visiting Patients to Prevent Airborne Infection in the Outpatient Department of a General Hospital

Visiting patients and medical staff share the same air in outpatient departments of general hospitals. In South Korea, 11 of 15 general hospitals operate with a fixed ratio of 20% outdoor air and 80% recirculated air even during peak visiting hours, causing the recirculation of indoor airborne pathogens. In this study, we propose a scheduling strategy in which air conditioning is adjusted proactively according to the number of visiting patients. The number of visiting patients was measured over five weeks with a people counter. The count showed a regular pattern: an increase in the morning, a decrease at lunch, and a sharp rise in the afternoon. Based on this pattern, we designed a pre-delay schedule for the air conditioning system in which the air intake rate is increased before the increase in visiting patients and maintained for some time after the decrease. The efficacy of this strategy was verified through mock-up room evaluations and full-plane CFD simulations. In the mock-up room tests, the pre-delay operation effectively suppressed particle accumulation in all three conditions. In the CFD simulations, the pathogen count in the waiting room during peak visiting patient hours decreased from the existing 12 particles/106 to 8.4 (−30.0%) with the scheduled operation and 6.8 (−43.3%) with the proposed pre-delay operation. Thus, the proposed method can be applied in existing facilities without modifying an installed central air conditioning system because primarily the air intake rate is adjusted within the airflow range that the existing central air conditioning system can deliver, without adding or modifying equipment.