Efficiency of a dirty air handler fan vs a clean one

[Badbird2000]

Can anyone point me in the direction of a document that can summarize the effects a dirty fan have over the efficiency vs. a clean fan? A dirty fan will increase the static required to operate and if too much builds up, could create an unbalanced fan leading to premature bearing failure.

Or am i just imagining all of this?

 

[walz]

Efficiency is the measure of the performance of a machine.
A dirty fan wont be able to privde the flow for which it has been designed for.

and yes you are right ,,, dynamic balancing of rotating equipment is important for the wear and tear of bearings. esp if RPM is high

 

[Artisi]

It is probably something like - clean fan, 100% of its maximum design efficiency, completely fouled fan maybe 0%.

Would assume what happens between clean and completely fouled is anyones guess and anyway, how would you measure the degree of foulness?

 

[willard3]

If dirt has built up on the fan blades, your coils will be dirty, too, decreasing the thermodynamic efficiency.

 

[Badbird2000]

Ok, thanks guys. Just wanted a voice of reason. I was writing up a summary of a building that had the filters crammed into the filter slots. The filters were not teh correct size. Air was able to bypass the filter and go straight to the coil and ultimatly the fan. The coil and fan were covered in dirt and grime (the job site is in Guam at the military base, and maintenance is just a big word to them, nothing else). The engineer proofing my report was questioning if the coils should be cleaned, and a dirty fan would have no affect on performance.

 

[mauricestoker]

I would say that the coils will need to be cleaned not only for heat transfer, but for indoor air quality and static pressure as well. From a maintenance standpoint, if the dirt condenses out and goes into the drain pan, then clogs the drain pan, you may have water damage as well. Having an excessively dirty fan is a good indicator that everything down stream has been exposed to the same levels of neglect, which can increase dollars and diminsh IAQ. If the air flow monitoring station, dP's, reheats, humidistats are dirty, then they can fail to operate properly and cause increased energy and maintenance costs.

From ASHRAE 62.1 (especially 5.5.1) the surfaces in the air stream are to be resistant to moisture and mildew growth. Maybe this kind of dirt is resistant to moisture and mold; where that dirt ends up should be a concern.