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COMMON TERMS
Lot A collection of units of a product of a single category, style, class and type manufactured under essentially the same conditions and from which a sample is to be drawn and inspected for conformance to specification.
Permeance The time rate of water vapor transmission through the vapor barrier expressed in U.S. perms [ng/(s·m 2 ·Pa)].
Pressure The positive or negative static pressure expressed in inches of water gauge (IWC) [Pa].
Radiated Noise The sound power level transmitted through the duct wall, expressed in decibels (dB).
Sag The distance deviation, expressed in inches per lineal foot [mm/m] of flexible duct, from a horizontal or inclined plane between suspension points on installed flexible duct.
Snaking Unnecessary directional change in any plane (horizontal, vertical, inclined) that produces excess pressure drop.
Sound Attenuation (Insertion Loss) The extent to which sound power level is reduced (attenuated) as it travels through a flexible duct, expressed in decibels (dB). Sound Generation The sound power level which is generated by the movement of air through a flexible duct, expressed in decibels (dB). Thermal Conductivity (k) The time rate of heat flow through unit thickness of an infinite slab of homogeneous material in a direction perpendicular to the surface, induced by unit temperature difference. Expressed in BTU - in./hr. - ft. 2 - °F [W/(m - °C)]. Thermal Resistance (R) The mean temperature difference, at equilibrium, between two defined surfaces of material or a construction that induces a unit heat flow rate through unit area. Expressed in hr. - ft. 2 - °F/BTU [(m 2 - °C)/W].
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Total Equivalent Length The sum of actual duct length and the equivalent length of fittings, bends, etc (see Equivalent Length).
Ultraviolet (UV) Light Invisible radiation in the electro - magnetic spectrum lying between visable light (380nm) and x - rays (100nm).
Vapor Barrier/Retarder The outer membrane of an insulated flexible duct.
Velocity The average time rate of air flow expressed in feet per minute (fpm) [m/s].
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