Friction loss on fabric duct system by DuctSox

Effects on velocity pressure, static regain and static pressure

Effects on the uniformity of the outlet air

Research done at the Mechanical Engineering department of Tennessee Tech University (TTU)

Same research lab trusted by ASHRAE to create ASHRAE’s Duct Fitting Database

DuctSox comparing two fabric duct systems:

› Fabric duct with an internal frame

› Fabric duct without an internal frame

Results:

› Pressure loss difference between two types of systems is very small

Static pressure is provided by the HVAC unit (AHU)

Inflation and operation of a fabric duct system is dependent on static pressure (SP), NOT inlet velocity

Velocity pressure (VP) is kinetic energy and slowly changes forms to a useful potential energy or static pressure regain (SPR) as the air travels down the constant diameter duct

For most systems, the pressure will be higher at the endcap than at the inlet due to SPR

In fabric duct system, SPR is common occurrence due to constant diameter sizing

Internal damper (or AFD) is used to adjust SP and reduce the pressure difference

AFD creates more uniform air dispersion through the whole length of duct

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