CFD analysis of the air supply rate influence on the aerosol dispersion in a university lecture room

The airborne droplet route has been recognized as the main pathway of infection transmission in indoor environments, drawing the attention to a proper design of Heating, Ventilation and Air Conditioning (HVAC) systems. This is particularly relevant for gathering spaces such as schools and universities, due to the high crowding levels and the long exposure times. Using 3D Computational Fluid Dynamics (CFD) numerical simulations based on a Eulerian-Lagrangian approach and validated against velocity measurements, the present study investigates the distribution over time of airborne droplets (aerosol) emitted in correspondence of the teacher position inside a lecture room, during a 2-h speaking activity (so reproducing a 2-h lesson), as a function of different air supply rates from the HVAC system. As the aim of the paper is to provide useful information for proper design and operation of HVAC systems, the room has been assumed to be empty. Results show that increasing the air supply rate is not always an effective solution to reduce aerosol concentration in correspondence of the positions occupied by the students attending the lesson. In fact, for the specific case under investigation, the aerosol concentration around the classroom seats does not always decrease when increasing the supply rates, even though the overall number of particles in the room decreases. This behaviour is mainly due to the asymmetric disposition of the seats with respect to the diffusers and extraction grilles, and underlines the importance of CFD approaches in investigating the fluid dynamics in indoor environments.