|About the Book|
The distribution of airflow to hoods in industrial exhaust ventilation systems often must be changed in response to changes in processes. Rather than taking the drastic step of reconstructing the ventilation system using the most optimum ductMoreThe distribution of airflow to hoods in industrial exhaust ventilation systems often must be changed in response to changes in processes. Rather than taking the drastic step of reconstructing the ventilation system using the most optimum duct diameters to achieve airflows and velocities, dampers can be employed to meet the latest airflow demands. Current damper adjustment procedures are notoriously tedious and challenging. These balancing methods, based on achieving target airflows one duct at a time, are iterative and time consuming since each adjustment affects airflows throughout the system. For that reason, by the time the last damper is adjusted, the first branches inevitably produce incorrect flows, forcing second and third rounds of adjustments.This study tested the accuracy of a proposed damper adjustment method that may be faster and more accurate than current procedures. The method is based upon predictions of ratios of the static pressures (SP) upstream and downstream of the dampers that should exist if the dampers were correctly adjusted. For this study, the necessary SP ratios were calculated using the target airflows and either published loss coefficients given the system characteristics or loss coefficients determined from baseline observed airflows and pressures. The dampers were then adjusted so that each ratio of measured static pressures was as close as possible to the target values for that duct. After the dampers were adjusted by this procedure, the resulting airflows were measured, and the deviations from target duct velocities were computed. The technique was tested on four airflow distributions, with one round of repeat measurements for each. The data was analyzed to distinguish between error due to the method itself and errors due to measurements.