Presentation of Branch Entry Losses in Industrial Ventilation Systems

Abstract

The present method of estimating branch entry losses in an industrial ventilation system, as given by the American Conference of Governmental Industrial Hygienists' Committee on Industrial Ventilation, assumes that branch entry loss is proportional to the velocity pressure in the branch duct and that no static pressure loss occurs in the main duct. The goal of this work was to study the interdependence of the velocity pressures in the branch, main, and combined ducts, using available experimental data, and to find a suitable method for graphically and mathematically presenting this interdependence. It was found that the static pressure loss in the branch does not correlate with the velocity pressure in the branch, as assumed in the currently used method. The total pressure loss in the branch (i.e., the sum of the branch's static and velocity pressures), however, does not linerally correlate with the branch's velocity pressure. When presented in this matter, each velocity pressure in the main duct is represented by a different parallel line and each assembly of branch, main, and combined ducts is represented by a different set of parallel lines. While the total pressure loss in the branch increases with velocity pressure in the branch, the total pressure loss in the main duct decreases with velocity pressure in the branch duct. In the latter presentation, each velocity pressure in the main duct is represented by a different parallel line.