Estimation of airborne infection risk in a school classroom according to operation of a floor-standing type ventilation system

Horizontal airflow, typically from floor-standing type ventilation systems used in school classrooms in some countries including Korea, may increase the risk of airborne infection. To estimate such risk, we conducted experiments in a classroom using simulated particles (DEHS) following the ventilation system discharge angles [upward (+45°), straight (0°), and downward (−45°)] and airflow rate (200 and 400 m³/h), along with desk partitions and simulated human heat release in a classroom. Calculations using the revised Wells–Riley equation showed that horizontal air supply potentially increases the infection risk by transporting particles [coarse (3.0–5.0 μm) and fine (0.5–3.0 μm)] over extended distances, from the air inlet to the back of the classroom. In comparison, downward air supply reduced the overall average infection risk by 30.1% compared with horizontal direction. Desk partitions yielded inconsistent effects, with short-term (5 min) and long-term (20 min) reductions in infection risk. However, when the internal heat gain increased, the average estimated infection risk decreased by 24.0%. Therefore, the risk of airborne infection could be reduced by changing the discharge angle of ventilation systems. Our findings could be useful in developing operating guidelines for existing ventilation systems or designing ventilation systems that reduce infection risk in classrooms.