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CHAPTER 2: COMMON TERMS
Air Barrier The membrane of the flexible duct which actually contains the air volume.
Air Connector A category of flexible duct not meeting the requirements of an Air Duct per UL 181 Standard (not tested for flame penetration, puncture and impact) and having limitations on use, length and location as defined by NFPA 90A and 90B. Air Connectors are identified by a “ round shape ” listing label of the listing agency. Air Duct A category of flexible duct tested and classified as to the Surface Burning Characteristics in accordance with the UL 181 Standard and identified by a “ rectangular shape ” listing label of the listing agency. Authority Having Jurisdiction The organization, office or individual responsible for and having final approval concerning use of flexible duct and its installation. Classification For purposes of this standard, a method of identifying, marking and specifying flexible duct as related to listing category, physical style, positive pressure class and velocity type. Equivalent Length Additional length added to the actual duct length in duct sizing calculations to account for the frictional resistance of fittings, bends, etc. (see Total Equivalent Length).
Excess Length The difference between the fully stretched cut length and the measured, straight - line, entrance - to - exit span length.
Flexible Duct A preformed, flexible, tubular passage for supply, return and exhaust air in HVAC systems. For purposes of this document, the terms designated Air Duct and Air Connector are used interchangeably, however not in their intended use and application. Friction Loss (Bends) The static pressure loss in bends of flexible duct, expressed as a dimensionless coefficient (Co) at a specified bend radius ratio. Co is a dimensionless coefficient which represents the ratio of the total pressure loss to the dynamic pressure in terms of velocity pressure. Friction Loss (Straight) The static pressure loss in a straight run of flexible duct, expressed in inches of water gauge (IWC) per 100 feet [Pa/m].
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Inner Core/Liner That portion of insulated flexible duct which determines the internal dimensions and inner physical form.
Installation Instructions A manufacturer ’ s printed instructions in accordance with the terms of their listing which advises the method and materials to install the flexible duct.
Leakage The time rate of air volume loss expressed in cubic feet per minute (cfm) [L/s].
Listed A published list by a recognized approving agency acceptable to the authority having jurisdiction stating that the flexible duct, tape, mastic, and clamp have been tested to and comply with the applicable Standard UL 181/UL 181B and maintains periodic inspection to assure production of the listed products are in accordance with the listing. Listing Mark/Label A printing, tag or other marking device of the listing agency permanently and prominently affixed to the listed product that certifies compliance to the applicable Standard UL 181/UL 181B and contains recommendations relating to installation and maximum physical conditions of use.
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