Effects of air exchange rate, particle size and injection place on particle concentrations within a reduced-scale room

Using aerobiology and engineering strategies to study particle movement in ventilated rooms is a powerful tool for understanding airborne disease transmission in healthcare facilities. More research is needed on movement of particles in ventilated rooms and more empirical data is needed to show effects of air exchange rates on particulate movement within a simple ventilated space. Results from this study can provide data for more complex strategies like Computational Fluid Dynamics (CFD) to help design ventilation systems in healthcare facilities where airborne disease transmission is a concern. In this study, particles were injected into a reduced-scale chamber to measure particle mass concentrations at twelve locations throughout the ventilated space and at the ventilation exhaust. Experiments had three particle sizes (1.9, 5.4, and 7.9 μm) of borosilicate glass, five levels of ventilation rate (nominally 2, 4, 6, 8 and 12 air changes per hour), and two injection locations (center and side). The ventilation system had one round inlet centered in one wall at ¾ height and one outlet in the opposite wall. Three replications were conducted for each combination of variables for a total of 90 tests. Increasing ventilation rates reduced concentrations of 1.9 μm particles in the occupied zone but had little effect on room concentrations of 5.4 and 7.9 μm particles. Exit concentrations for 1.9 μm particles were higher than for 5.4 and 7.9 μm particles. For 1.9 μm particles, average concentrations decreased linearly with increasing ventilation, while similar trends were not seen for the larger particles.