Static Pressure Loss in Flex Duct Systems 1

[Agator82]

I am a draftsman/designer at an engineering firm, and most of my work is in HVAC Mechanical System design. We recently did a project for a small school house where the contractor installed ALL flex duct instead of the hard duct we specified.

Typically, we would kick it back and have the contractor redo, but because we were not contracted for Construction Review and the installation was approved by the owner against our recomendations this installation will stay.

Although, I am working on As-Built drawings for the project and I am looking for a table that will give me Static Pressure Loss of Flex-Duct. At this time I am unable to find anything that will provide me with the information I require to verify that this system will perform appropriatley. If someone can shoot over a message I would greatly apreciate it.

 

[lilliput1]

See SMACNA HVAC Systems Duct Design. The 1990 Issue page 14.8 Table 14-1 Duct Material Roughness Factor shows flexible duct to be classified "Rough". Page 14.9, Figure 14-3 Duct Friction Loss Correection Factors shows correction factor for "Rough" varies with velocity & diameter. Check if your office have a copy of the above SMACNA book.

Make sure you count elbows & bends. A 45° elbow is considered to have 0.6 X the pressure drop of a 90° elbow.