Optimization of Aerosol Sensor Placement in Common Ventilation Ductwork

Aerosol detection in HVAC duct components is a critical component of contaminant detection and analysis. Incorrect placement of a sensor inlet within the ductwork can have a significant, deleterious effect on capture efficiency and sample accuracy. Computational fluid dynamics studies were conducted of straight rectangular cross-section ductwork and a 90° bend to determine flow patterns and simulations of particulate injections were made at various locations across the inlet. The resultant particle distributions were analyzed to determine the optimal placement for a sensor inlet. The study demonstrated that, for the geometries studied, the optimal location for a sensor inlet is approximately ½ to ¾ of a duct diameter downstream from the interior corner of the bend, centred laterally within the duct, and at approximately 2/3 of the duct height. These results were experimentally verified using ductwork constructed in a laboratory environment using a polydisperse aerosol and commercial particle counter.