Assessment of the effect of indoor air stability and airflow field on the multi-person infection risk.

The transmission of pollutants and viral aerosols is an important way to cause indoor respiratory infections. Influence of ventilation modes and indoor air stability (IAS) on infection risk of the sitting breathing microenvironment of four people were simulated by CFD. Ventilation efficiency and infection risk were assessed using the contaminant dispersion index (CDI) and a Wells-Riley model based on SF6. The results show that unstable, upper supply and lower return contribute to the uniform indoor airflow and the average indoor wind speed is approximately twice that of other working conditions. Under the upper supply and lower return, the average SF6 concentration in the breathing microenvironment under unstable condition was 20.4 % lower than stable condition. Unstable can increase the intensity of turbulent fluctuations, enhance vertical diffusion, break the accumulation of pollutants, rapidly dilute and remove SF6 in the breathing microenvironment. Upper supply and lower return can reduce the average CDIb by 30-65 % within 15-30 min under unstable condition which has the strongest pollutant diffusion capacity. Under stable condition, the transient infection risk at the location next to the infected person is lower than that under unstable condition. Ventilation strategies and indoor air stability will have an impact on infection risk after 16 min. The combination of upper supply lower return and unstable condition can reduce the infection risk of three susceptible individuals by 51.3 %, 35.6 % and 11.4 % than that under stable condition, respectively.