Propeller Fan Versus Centrifugal Fan For Exhaust

[SRBKDW]

Wanted to get folks opinion regarding best fan for an exhaust application. Purpose of exhaust fan is to control static pressure in the building. The building will be in full economizer ~70% of the time. When the building is in full economizer the exhaust fan will run. The exhaust fan will be sized in the 5,000 cfm to 8,000 cfm range. I'm still determining the final size.

I'm considering either a propeller fan or a centrifugal blower.

Thanks in advance for you advice and ideas.

 

[ChasBean1]

The fan will depend on friction in the return that needs to be overcome. If there is very little, probably a propeller fan (simple, like a house fan) would do - not meaning one of those manly vane-axial propeller fans. If you have to overcome some suction friction, there would be a variety of options but the centrifugal would then be better than a propeller fan. A plenum fan (i.e., plug fan) is often a good option if directional outlet flow is not of high importance.

If this isn't built yet, have you considered an AHU with a return fan and an economizer cycle?

 

[SRBKDW]

Just to clarify the exhaust fan will be located very close to an outside wall and will have a duct run of ~10 feet before it exhausts to the outside so the static pressure will be quite small.

 

[ChasBean1]

So my question to you is do you even need the fan? What will the maximum pressure in the building be with this opening (say, equipped with gravity dampers) alone?

If you decide that the opening is too small to limit rise in building pressure, this sounds like a job for a propeller fan.

 

[friartuck]

From a noise point of view the centrif is better but 3x the cost of an axial fan. Axial fans are temperamental and have to be properly sized and carefully positioned. They have to be given good inlet conditions and generally generate low pressures (up to 250Pa or 1" is easily attainable but higher pressures of 1000Pa or more are achievable if the fan speed is 2 pole 2900RPM)

If cost is the main factor then go for an Axial multi Wing but if you are a consultant and want flexibility (i.e.belt change on the centrif pulley) then go for a backward curved centrif. They dont over-load. On the duties you have, you could possibly go for an inline backward curved fan

See NuAire Ltd. UK

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