Experimental investigation of power loss coefficients and static pressure ratios in an industrial exhaust ventilation system

A study tested whether measures of equivalent resistance (X values) and rat ios of static pressure (SPratio) for given ducts of contaminant control exh aust ventilation systems were independent of substantial changes to airflow level and to changes to resistance of other ducts within the same full-sca le five-branch system. In a factorial study design, four airflow levels wer e achieved by changing fan rotation rate while resistances to flow for spec ific branch ducts were changed independently by adjusting slidegate dampers to various settings. For each damper insertion depth (including fully open ), the results demonstrated substantial invariance for branch X values (few greater than 5%), SPratio (few greater than 3%), and fraction of airflow t o each duct (few greater than 2%). X-values for submains were much less sta ble, changing by 20% or more with changes to other parts of the system. For the same conditions, hood static pressures changed by as much as 96% (with standard deviation of 40%). The results suggest that before and after valu es of X and SPratios should be more reliable bases for indicating alteratio ns than comparison of observed static pressures. The stability of airflow d istributions with substantial changes in airflow suggests that one could ad just airflow distribution (e.g., with dampers) without considering whether the fan speed was set correctly, leaving fan adjustments for a final step.