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A numerical model intended to verify the accuracy of a flexible-duct pressure loss calculator nomograph is described. In order to assess the influence of flexible-duct compression on pressure loss and to compare the pressure loss of wire-wound flexible ducts to that of round galvanized-steel ducts, a parametric study was performed over a prescribed flow-rate range for airflow in sheet-metal ducts of varying diameters. The influence of flexible-duct compression was accounted for by means of a pressure drop correction factor (PDCF). Equivalent flexible-duct diameters that produce the same pressure loss per unit length as rigid sheet-metal ducts were determined. Flexible ducts must be increased in diameter relative to sheet-metal ducts in order to exhibit the same pressure loss per unit length at a given air-volume flow rate. The analysis was limited to lowpressure applications typical of residential air-duct systems.

Citation: ASHRAE Transactions - Volume 121, Part 1, Chicago, IL