Adjustable dampers offer an apparently simple and inexpensive way to redistribute airflows in ventilation systems to meet the changing needs of an otherwise fixed system. However, current damper adjustment procedures are notoriously tedious and time-consuming, which is greatly exacerbated by the typical need for two or more rounds of adjustment.

This study tested the accuracy of a previously proposed damper adjustment method 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. The prediction method employs airflows and pressures observed in the installed system when all dampers are open. The dampers were then adjusted so that each ratio of measured static pressures was as close as possible to the predicted values for that duct. After the dampers were adjusted by this procedure, the resulting airflows were measured using standard Pitot tubes and a calibrated digital manometer. Observed and predicted duct velocities were compared for four airflow distributions, with one round of repeat measurements for each. Considering data normalized to the same total system airflow, some branch airflows were changed by as much as 42%. The average change from baseline to predicted velocity in branches was 23%, considering both positive and negative changes, with a standard deviation of 17.9 %.

Of the sixty-four predicted airflows, the mean of the absolute value of the error was approximately 2.1% of the target value. The standard deviation of the positive and negative errors was 1.7%. Therefore, roughly 98% of the branches had errors that were less than 5%, either above or below the target velocities. The largest single error was 7.35%. Generally, in ventilation balancing practice, methods that achieve accuracy within 5% are deemed successful.