Inlet velocities for Centrifugal Fans

[mwpeters49]

What is a reasonable range for inlet velocities for the inlet of a centrifugal fan. My discharge velocity is about 2,850 fpm at 1" W.C. static pressure. Is an inlet velocity of over 4200 ft/min excessive?

 

[willard3]

At these higher inlet velocities, prerotation and fan effects will increase pressure losses. Noise will also be a problem.

Check AMCA and ASHRAE for fan inlet conditions.

 

[curtis2004]

mwpeters49,

Acceptable inlet velosity depends on density (temperature) of medium. What is application of the fan? Can you give more details of medium (temperature, density) and fan (inlet/outlet size, class, motor HP)?

regards,
curtis

 

[mwpeters49]

Curtis,
This is for a HVAC application, specifically for a Industrial Evaporative Cooler. Discharge pressures are low, about 1" w.c. static or less and using a size 36 I figure we need a 7.5 hp motor. The medium is air and we will be at STP, 0.067 lb/ft^3 at 70 F.

 

[curtis2004]

4,200 ft/min seams high. Usually if there is no other specific requirement I would keep it around 2,000 ft/min for air at 70 F.
Regards,
curtis

 

[ChasBean1]

If you're talking about the inlet bellmouth of a fan, up to 15K fpm at this location is not at all unreasonable.

It's an easy issue to resolve - check out the mfr. flow design vs. open inlet area of the fan provided...