Airborne infection risk in classrooms based on environment and occupant behavior measurement under COVID-19 epidemic

The changes of indoor environment and occupant behavior (OB) are two main causes for the gap between predicted and actual airborne infection risk. To improve the accuracy of COVID-19 airborne infection risk assessment, the environment (CO2 concentration) and OBs (occupant area per person (OA) and activity level (AL)) in three typical classrooms of a primary school in Tianjin, China was selected to conduct the on-site measurement. Based on the measured data, a modified Wells-Riley model was proposed to predict the infection risk, and a risk-controlled ventilation strategy was developed to calculate the ventilation demand. Results indicated that classrooms in the breaking time (B-T) showed a lower indoor CO2 concentration (C in), larger OA, and higher AL than in the teaching time (T-T). The variation tendency of the calculated infection risk increment in T-T was consistent with C in while in B-T was significantly affected by OA and AL, and the maximum fluctuation extent in B-T was two times of that in T-T. Moreover, to avoid the risk spreading in classrooms, a feasible solution of dynamic ventilation control based on the real-time infection risk was proposed, thus facilitating to provide a healthy and sustainable environment for students in classrooms.