Airborne transmission in a meeting room with mixing and displacement ventilation

The main purpose of this study is to analyse the effects of heat gain, airflow rate, air distribution, and the location of an infector on the airborne transmission and infection probability in a meeting room. In a six-person meeting room the droplet nuclei of an infected person were simulated with tracer gas (SF6) generated by a thermal breathing manikin. An overhead perforated duct (OPD) and low velocity unit (LVU) were used and their performance was compared. With OPD, the average contaminant removal efficiency in the breathing zone was quite uniformly between 0.9 and 1.1. With LVU, the average contaminant removal efficiency varied greatly between 0.2 and 10.1. The airborne generation was assumed to be 5 quantum/h by an infected person. The infection probability for every exposed person was found to be quite uniform with OPD, 1.4% with a heat gain and air flow rate of 38 W/m2 and 61 l/s and 0.9% with a heat gain and air flow rate of 60 W/m2 and 116 l/s after three hours’ exposure. However, variation of the infection probability with LVU was significant and the highest risk reached 4%. The infection probability was lower if the exposed person was farther from the infector, or in the case of OPD if the infector was near the exhaust. With LVU, the infection probability depended on the airflow rate and the relative distance between the supply unit and the exposed person.