Flat Oval Spiral Duct Deflection

Abstract

The deflection of a spiral duct depends on its flat span, gauge, pressure, and reinforcement. Furthermore, the duct weight determines the cost of installation, not only in material costs but also labor, which is bid by the duct weight. The current duct deflection standard, the rectangular-duct construction standard, does not accurately represent flat-oval spiral ducts. Therefore, the objective of this project was to perform those experiments necessary to support the development of a standard for the installation of flat-oval spiral ducting. Also in support of standard development, the project developed empirical models to represent unreinforced ducts for positive and negative pressures along with T-25 ducts for positive pressures. In conclusion, the development of a flat-oval spiral duct deflection standard is important to the HVAC industry, because it would allow engineers to perform reliable duct design with a focus on reductions in material and installation cost. The collected data, empirical modeling, and data analysis that has resulted from this project will form the foundation for development of a flat-oval duct deflection standard. Specifically, the project reported herein resulted in deflection-pressure data for a broad range of un- reinforced and reinforced ducts. The test matrix was designed to provide sufficient experimental data to develop empirical deflection models for unreinforced ducts and T-25 positive-pressure ducts. In addition, a more limited test matrix for other rein- forced ducts allows for qualitative analysis and empirical observations. The contour plots, constructed with the aid of empirical models, can be used to identify duct sizes and types that satisfy deflection criteria at specific pressures, which is a major step in developing duct standards.