Exhaust Fan Motor "Burning Up."

TwoBlocked

TwoBlocked

Senior Member
Location
Bradford County, PA
Occupation
Industrial Electrician
We have a client that complains about an exhaust fan motor that keeps "Burning Up" because of high ambient temp. It is in a gas compressor building above a large internal combustion engine. And yeah, it gets pretty toasty in there. I've reached out to a supplier, but wanted you fine folks' ideas, too.

The motor is a Baldor, 230V, single phase, 184T frame, 2 HP, 1750 RPM, Class B insulation, capacitor start, explosion proof. Don't know what sort of controller, yet. Might just be a breaker. I got looking on line for one with a higher insulation class, but can't find much. Seems there are few choices in single phase.

Sooo .... am looking for options if a single phase motor with a higher insulation class is not available. What do you guys think of:

Upping the motor/controller to 3 HP that would generate less heat
Installing a VFD so that a 3-ph motor with a higher insulation class can be used
Other options?
 
Verify the classification of the area. If it’s D2, you can likely use a 3 phase motor that’s not explosion-proof, giving you more motor options.
But I agree with others, a redesign of the ventilation system to get the motor out of the heat would be ideal.
 
Some options:

Agree with @ptonsparky use a supply blower if the space can be pressurized.

If not use a larger blower on the roof and mix some outside air into the duct before the motor

Use an exhaust fan with the motor outside the duct, blower in the duct belt drive
 
The suggestions do make me think.

A supply blower wouldn't do much of anything. These building are glorified pole barns. Impossible to create a positive pressure inside them. I doubt changing the duct work is an option. The design is engineer approved, and not easily changed.
 
What type of fan? an axial with a blow open vertical shutter? A gravity blow open vertical shutter is a poor choice, eats up a lot of HP and restricts airflow. Motorized damper would be less restrictive, but would need a timer to open it before the fan starts.

Single phase motor is a poor choice, explosion proof is even worse. sealed up like a drum for ventilation.

The ideal way to deal with excessive heat is to use a blower or fan that is belt driven, with the motor outside of the airway.
Is the existing motor fully loaded? A larger motor would be the same amount of heat for the same work, slowing down the fan speed (sheave change) would reduce load. If it's a direct drive type, increasing motor HP doesn't change much, especially with explosion proof.
 
WireBiter said:
I am an hvac guy, so I gotta throw it out there: check your venting is clear.

If it is blocked, I bet it'd just keep burning up. Could just be a birds nest or beehive keeping the air blocked. Maybe Hopefully an easy fix.
Click to expand...
You may be right. They keep having this same problem with this same fan, but there are other identical ones in the same building. I'd of thought they would check that when replacing them, but maybe not ... Hmmm ...
 
ptonsparky said:
Why would a motor that sits in 200 degree ambient run cooler if it's larger?
(Random #)
Click to expand...
A typical nameplate will say that the motor at full load will run at 40C higher than ambient temp. But if a motor is NOT at full load (by upping the HP with the same load) I expect it would run LESS than 40C above ambient temp. That's my thought and and looking for comments on it.
 
TwoBlocked said:
A typical nameplate will say that the motor at full load will run at 40C higher than ambient temp. But if a motor is NOT at full load (by upping the HP with the same load) I expect it would run LESS than 40C above ambient temp. That's my thought and and looking for comments on it.
Click to expand...
IMO, Ambient is going to be the deciding factor.

Are the bearings failing? Start or run windings? Have the capacitor(s) failed? How often does it cycle? Belt driven fan? Who tightened it? Same guy? Have they changed the pulley ratios?
 
WireBiter said:
I am an hvac guy, so I gotta throw it out there: check your venting is clear.

If it is blocked, I bet it'd just keep burning up. Could just be a birds nest or beehive keeping the air blocked. Maybe Hopefully an easy fix.
Click to expand...
Had that issue yesterday hvac claimed motor was bad and overheating- no one cleaned the ducting air could go no we’re. So much for qualified hvac tech there lol
 
ptonsparky said:
IMO, Ambient is going to be the deciding factor.

Are the bearings failing? Start or run windings? Have the capacitor(s) failed? How often does it cycle? Belt driven fan? Who tightened it? Same guy? Have they changed the pulley ratios?
Click to expand...
Er, I went to check things out yesterday. There was some confusion and ended up looking at a bad fan motor elsewhere...

That never happens to any of you guys right? RIGHT???
 
TwoBlocked said:
and ended up looking at a bad fan motor elsewhere...
Click to expand...
And you tell us previously that it only happens to this fan.
The others run fine. 😉

Seriously if you want better suggestions, you need to submit better data. I wired and serviced industrial ventilation systems for many years. If you think the Easy solution is the next size up hazardous motor, order it done and tell us if it works.
 
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