Pressure loss characteristics of thin single-blade flat dampers for square airflow branch ducts

Abstract

This paper describes an experimental study of the pressure loss characteristics of thin, single-blade flat dampers in square branch ducts in the turbulent region. The damper pressure loss characteristics and the interactions between the damper blade and shaft have been studied at various damper width ratios to take account of the damper leakage effects. At damper angles > 10 °, the damper pressure loss characteristics determined for damper -width ratios of 0.5 to 1.414 are found to be independent of the shaft sizes for typical rectangular and circular shafts with blockage area ratios ≤ 0.16. The damper pressure loss coefficients are observed to have collapsed onto a single curve within a ±10% accuracy for damper width ratios of 0.9 to 1.414. By applying this relationship to square, flat airtight dampers in square branch ducts, the desired flow characteristics for branch ducts fitted with proportional damper controller-actuators can be achieved within a maximum deviation of ±10%. This helps solve the nonlinearity problem in the installed damper characteristics for large, complex, variable air volume systems having branch ducts with different resistances. Using a graphical approach, the required tuning parameter values for square, single-blade airtight dampers have also been determined for use by control system designers.