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Effectiveness of the “Common” Method in Balancing Exhaust Ventilation Systems. Vivek Balasubramanian Dampers are used to adjust the distribution of airflows in duct systems. The “common”(i.e., most commonly used) method is to adjust each damper in turn so that the airflow through its branch equals the desired level. Typically, the airflow through each branch duct is estimated from the centerline velocity pressure. To test the effectiveness of that approach, dampers were adjusted on a seven branch, full-sized experimental duct system. After adjusting the dampers for a given condition, the percent excess airflow (%Qexcess) for the system was estimated as the amount above the ideal fan airflow that would exist if the fan speed were adjusted so that the lowest ratio of airflow to airflow goal for any branch was unity. The lower the value of percent excess airflow, the more perfectly balanced the system was. The results varied with the level of the target airflows. The excess airflow was least (5.3%) for the low airflow system. The excess for the moderate (8.5 %) was greater than the excess for the perfect targets (6.56%). These values were much higher than the mean value of 2.13% found by Dodrill (2004) on the same system for the “SPh Goal Ratio” method proposed by Guffey (2005). The pressure in the system was measured. As expected, the pressure in the system increased as the dampers were choked down to achieve the targets.

26. Effectiveness of the “Common” Method in Balancing Exhaust Ventilation Systems