Velocity of Reuturn AIR Duct 1

[irfansiddiqui]

What Should be the standard return air velocity for an AHU of 29,000 cfm

 

[willard3]

There is no standard velocity.

Duct velocity has many variables, a couple, just to start

Noise
Carrying material?

 

[cdxx139]

low pressure
or
medium pressure
system?

knowledge is power

 

[irfansiddiqui]

Low pressure

 

[Drazen]

This will give you picture:

http://www.engineeringtoolbox.com/duct-velocity-d_928.html

but your still need engineering judgement on prevalent criteria, velocity is only one possible criteria for duct sizing, than place of application, and you finally need to separately consider main duct, symmetrical or asymmetrical branches, runouts, and finally you need to perform enough calculations to make sure that network balancing will be possible at all.

i am saying all this to give you idea that sizing ducting based on mere velocity, especially based on one figure is totally wrong, it can be only initial step in iterative calculation.

though, i must admit such an approach gives me more job sometimes . clients call me to "solve problems with their ductwork" which makes necessity of first drawing as-built, than performing lot of calculation in attempt to retain as much a possible of existing ductwork. that can be charged say three times more than normal fee.

did you ever visit exclusive restaurant where there is apparent large stain around number of celiing diffusers close to one corner, to find out that corner is closest to ahu? that can possibly mean ventilation effectiveness is near zero.

industrial environment has different problems, some people insisti on velocity method though static regain could save them costs.

 

[willard3]

You would do best to consult an Engineer familiar with ventilation systems.

If you try to bootstrap this, it will bite you in the butt.