The potential of local exhaust combined with mixing and displacement ventilation systems to mitigate COVID-19 transmission risks

The performance of two types of air diffusers, a perforated duct and a low-velocity unit coupled with local exhausts, on airborne transmission and cross-infection was investigated in a meeting room. The effect of air diffusers’ locations on airborne transmission was investigated. Six local exhausts were installed above six workstations at 2.0 m height. Respiratory-generated airborne pathogens were simulated using SF₆ in the exhaled air of the manikin acting as an infected person. The SF₆ concentration in the inhaled air of five susceptible persons remained steady with perforated duct located on the ceiling and at 1.7 m height attached to the corridor wall, but fluctuated greatly when perforated duct were located on the floor, although with a much lower concentration level. The perforated duct under the warm window showed the best potential for mitigating airborne transmission. The concentration in the inhaled air was varied with horizontally supplied low-velocity unit, but much steadier with low-velocity unit at 1.7 m attached to the wall. With an adjusted airflow pattern from low-velocity unit, the inhaled concentration was much lower and uniform among the five susceptible persons. The contaminant removal effectiveness (CRE) was 4.3 with perforated duct under a warm window on the floor. With an adjusted airflow pattern from low-velocity unit, the CRE was much more consistent and increased from 2.1 to 3.9 with an airflow rate from 61 l/s to 116 l/s. The infection probability was the lowest with the perforated duct on the floor and adjusted low-velocity unit.