Particulate concentrations within a reduced-scale room operated at various air exchange rates

Precise prediction of particulate movement is needed to provide a better understanding of how airborne disease organisms move within ventilated facilities. Bacteria often adhere to larger airborne particulates, which will modify their movement behavior in ventilated rooms and may provide an environment to allow them to remain virulent longer. An empty chamber (206 H × 203 W × 386 cm L) with a circular air inlet and outlet on opposite ends was ventilated with air that had a known particulate density. The inlet and outlet openings were sized to maintain inlet and exit velocities at around 5.1 m/s at 5 different air exchange rates (around 2, 4, 5, 9, and 14 air changes per hour - ACH). Particulate concentrations were measured at the air outlet and at 12 locations within the chamber. In this study, the particulate concentration in the inlet air remained constant, so the amount of particulates injected into the chamber increased as the ACH increased. The measured particulate levels at the outlet also increased essentially linearly with an increase in ACH. However, the particulate concentrations in the occupied zone of the chamber did not increase linearly with an increase in actual ACH. Rather, it increased essentially linearly at the lower ACH levels (from around 2 to 5 ACH), but then leveled out at the higher ACH values. The advantages of increasing ACH in terms of providing better environments in the occupied zone of rooms may have limits, which warrant further investigation.