Direct drive or Belt drive fans?

[Vince79]

Hello everyone,

I found out about that post on this forum:

http://www.eng-tips.com/viewthread.cfm?qid=178077&page=65

which also talks about the kind of fans to choose but I didn't find my answer.

I'm currently designing an HVAC for a food processing company in a class 100,000 room. I'm talking about high airflow above 10,000 CFM.

I chatted with some suppliers and other designers and one of them told me that:

- direct drive fans are more efficient than belt driven fans (80% vs 60%)
- direct drive fans cost the same as belt driven fans
- belt driven fans challenge the filters very much because of dust coming from the belt

(That guy was not a direct drive fan supplier)

So I would like to know your opinion about that. Which one is better ? Is everything true ? What about maintenance ?

(Please excuse my terrible english)

 

[BlueSandman]

I used to build automotive paint shops, so "clean" has a very high bar for me as any dirt in the paint can force a production re-run.

I always used belt driven, housed fans (ducted inlet and outet). That design keeps the belts and all the fan nooks and crannies (future dirt pockets) completely out of the airstream. Additionally, the motor heat and noise are removed from the airstream. You might need to add a flexible inlet and outlet collar.

You will likely hear several opinions on fan efficiency. Belts and drives will drop the efficiency (by about 2%) for heat and slip. I suspect the 20% loss you hinted at above does not compare the recommended fan selections for each design.

There is probably slightly more maintenance on a belt driven fan (two more bearings to lubricate, belts to tension). But I think the design is service friendly in my arrangment because all of that can be done while the equipment is running (as opposed to the motor being inside the air handling unit, which are only accessable durring down-time).

 

[Vince79]

Thanks for your quick reply BlueSandman,

Belts and drives will drop the efficiency (by about 2%) for heat and slip. I suspect the 20% loss you hinted at above does not compare the recommended fan selections for each design.

I didn't quite understood that part, what do you mean by "drop the efficiency for heat and slip"?

Do the paint shops you built had a specific air class?
What were their sizes (volume)?
How much were the airflows?
How big were the ducts (diameter)?

 

[willard3]

If you need to replace the motor on a belt-drive fan, you can. With a direct drive, you must st replace both the fan and the motor.

Belt-drive fans are easy to balance w/o a variable frequency drives.

 

[ChrisConley]

'drop the efficiency for heat and slip' refers to belt transmission losses. (parasitic bending hysteresis and sliding friction).

I agree those losses may be as low as 2% at design conditions, but poorly maintained (loose) belts can waste a lot more energy.

Easier to balance a belt drive (you can shiv change a fair bit), but as willard3 mentions, with a VFD direct drive fans are pretty easy to set up as well.

 

[Vince79]

Thank you for your answer willard3

I have found out this PDF about belt drive VS direct drive

ziehl-abegg.com/us/download-2100.html

In this PDF, they listed the advantages of direct drive fans:

- No transmission losses -> Less power required
- No belt residue -> Elimination of filter
- No maintenance -> Reduced operating costs
- Easy to clean -> Better hygiene
- Lower load on motor bearing -> Longer life time
- Low vibration levels -> Smooth and quiet operation
- Motor directly connected to wheel -> Compact, space saving design
- No bearings in the fan inlet -> Higher performance
- Reduced weight -> Easy handling

All of them make sense except maybe for "No maintenance", but like you said willard13, if you need to replace a part of the direct drive fan, you have to change the whole thing so they're making a point here.

I don't know why it's easier to clean but it really seems that direct drive fan is a better technology than belt drive fan...

For your information, that PDF comes from the ZIEHL-ABEGG company which also makes belt driven fans so...

 

[SAK9]

Apart from the reasons mentioned above,I would go for a direct drive for the clean room application if the fan is in the air stream.For a class 100k it is likely that the fan is down stream of the filter.Further belt drive is less reliable and adds to the maintenance cost

 

[Vince79]

Thanks for all of your answers.

My choice has been made and I will go for the direct driven fan which has a lot more advantages than the belt-driven one.