High velocity of PVC duct

[sfxf]

In the project I am working on, the client wants to use the existing PVC duct in stock for clean cold air delivery. But at that specific size, the velocity of air flowing through the PVC duct will go up to 3500 fpm (it is not fume exhaust application, no any hazard particles in the air stream), and I think they need to use bigger size of PVC duct. Can anyone advise if I am on the right track? I understant the pressure drop through the duct will be high with 3500 fpm, but how about the fan has enough static pressure to overcome the total pressure loss? Any noise issue? Anyone has experience that what will happen for PVC duct with air flowing through at 3500 fpm velocity? Thanks a lot!

 

[PhilBW]

sfxf:

There will definitely be a noise issue at that velocity, especially if the duct is delivering supply air to an occupied space.

You should also point out to your client that he will spend a great deal extra in energy costs at the higher velocity. Horsepower is proportional to the square of the velocity. If the smaller ductwork doubles the velocity of the air, the fan will require 4 times as much energy. If the motor is fairly large, that will add up quickly.

Phil

 

[SAK9]

Static electricity generation is a possibility which can be a hazard in an explosive environment

 

[Drazen]

When looking at my clients, when they come to some idea you can convince them to give up only if there are some legal issues.

You can inform your client that enetgy costs will be higher with so high velocity so it is up to him to decide, your duty is to inform him.

But it is noise what should require attention because such velocities are acceptable only within industrial rooms that are noisy anyhow. For any kind of office environments noise on this velocity will be a problem.

 

[sfxf]

Thank you all!

 

[tombmech]

There may be a legal issue - depends on where that PVC duct is located - it could be against NFPA codes. Typical supply duct in commercial structures is in a return air plenum, and PVC would be disallowed.