Dust Collector Closet & Cooling

[Peter Aeschliman]

Hi All,

I'm slowly making progress on my basement shop build out, which will include a dust collector closet for my 3HP cyclone to reduce noise. I will be venting the exhaust air outside (I've done a ton of research and I'm aware of the trade offs and other considerations). I've completed the framing for the closet.

My question is: Will the motor get hot enough in the closet that I will need to cool it? If so, have any of you figured out a clever way to do this without letting lots of noise out of the closet? Soundproofing is the point of the closet after all...

I imagine I would need an inlet and an outlet (one up high and one down low) to keep the air circulating. I've seen some mentions about this online, but they tend to be light on details.

Thanks in advance for your advice!

[Lee Schierer]

It will depend upon how long and how often your run the DC. If you are only running for an hour or two, I doubt the air in the closet will get hot enough to affect motor life. If you plan on running it all day it will get pretty warm but still may not be a problem. One idea you be to put a remote reading thermometer in the closet to measure the air temp and if it looks like it is getting warmer than you like you can shut the system off for a while.

[Peter Aeschliman]

Good idea on the thermometer. Thanks!

[John K Jordan]

Peter,

i have my 5 hp DC in a 4x8 insulated closet with a 5 hp air compressor. I wondered about the heat too but so far I can't detect any heat buildup.

The ClearVue forum has discussion about this. All the advice I read was for a filtered unit which returned air to the shop. In that case they mounted the air return duct opening high on in the closet near the motor with the theory that the return air would have to move past the motot, cooling. However, like many theories people implement which sound good, I have not seen where anyone actually did the heat calculations or did a test to compare with other configurations. Also, what are the operating environmental specs on the motor, how much heat are they designed to take?

if elevated temperatures turn out to be a problem a pair of screened openings to the outside, one high and one low could provide circulation. An intake fan could be controlled by thermostat if needed, or switch a fan on automatically with the DC.

An inexpensive thermostat like this could either switch on a fan or simply turn on a warning light or buzzer in the shop:

http://www.amazon.com/gp/product/B000E7NYY8

JKJ

[Charles Lent]

Motors are normally spec'd with a certain temp. rise. Look at the plate on the motor. It will likely have this. The temperature specified is the degrees of rise above ambient, not the operating temp. and it's usually marked in Centigrade. You need to add the motor label degrees to the ambient temperature to find the operating temp. that is maximum for the motor. A quick test is - Slightly above "too hot to hold your hand on" and this is usually acceptable. The formula is typically like this 25 c (ambient) + 40 c (rise from motor label) = 65 c (real operating temperature).

Charley

[Gary Radice]

Since you have already done the framing, my suggestion might not work for you but what I did was leave a space between the back wall of the closet and the wall of my garage. I vented the closet high near the motor, then down the space behind the closet and out the side near the floor. That gave the exhaust air a longer path to dissipate noise before returning it to the room.
I agree that if you are running the DC for short periods of time the heat buildup might not matter. I will say that with my 5 HP cyclone the exhausted air is noticeably warmer than the intake air after just a few minutes of operation.

[David L Morse]

The NEMA default ambient temperature for motor ratings is 40°C (104°F). The heat produced by a 3HP motor at 80% efficiency is about 2000BTU/Hour. If you're good with R values and heat loss calculations you can estimate the temperature rise in your closet. If adding the temperature from an average day you're less than 104°F and maybe no more than 120°F or so for your hottest days then you should be good.

Remember that for insulation life on a motor there's no cliff to fall off of, it's a smooth curve. The variation in lifetime is approximately a factor of two for a 10°C change. If your average temperature is 45°C instead of 40°C then you get about a 30% reduction in insulation lifetime.

Charles brings up another important point. The actual temperature rise of a motor is rarely as high as is allowed for it's insulation class so that can give you some additional margin. Look at the nameplate. For example, a motor with Class F insulation might have a full load temperature rise of 85°C compared to the 105°C allowed. This gives you an additional 20°C cushion. While you probably shouldn't use all of it because of decreased efficiency at higher temperatures it will put you close to 60°C (140°F) ambient while still getting the often quoted 20,000 hours from the insulation.

Of course for me anything that remotely resembles a closet gets lots of shelves for storage so I would certainly ventilate it. I don't want to store finishes and adhesives at 140°F, not even 104°F if I can avoid it.

[Peter Aeschliman]

Thanks everybody! Very helpful. i'll have a look at the motor and let you know what i find out.

[Peter Aeschliman]

http://i66.photobucket.com/albums/h255/peteraeschliman/20151213_163948.jpg (http://s66.photobucket.com/user/peteraeschliman/media/20151213_163948.jpg.html)

Looks like the motor can tolerate a rise of 140 degrees Farenheit.

I think I'll try without any venting, measure the temp, and see how it goes.

[David L Morse]

Looks like the motor can tolerate a rise of 140 degrees Farenheit.

A bit less than that. Class E is an IEC insulation class, not NEMA. It's maximum temperature rating is 120°C. So 120° - 10° hotspot allowance - 60° rise = 50°C (122°F) maximum ambient.

If you installation will be like many with the motor close to a ceiling then be sure you monitor the temperature close to the motor and at ceiling height. That way you'll know the temperature of the air going into the fan intake grill at the back (top) of the motor.

Also, at higher ambient temperatures the starting frequency has to be reduced. Most starting capacitors are rated at 20 starts per hour maximum because of internal temperature rise. Since you are putting in the effort to quiet your DC I would guess that you'll be turning it on and letting it run rather than cycling it after each operation and that's the best way to use it. As always, motor capacitors should be handled as maintenance items and you DC installation should allow for easy replacement.

[Peter Aeschliman]

Ah. So what I think you're saying is that the 60° degrees on the plate is not the allowable rise above ambient, it's the max temp INCLUDING the ambient temperature. I misunderstood... but that makes a lot more sense.

I'll make sure to stick the temp probe at the same height as the motor.

As for starts and stops, I will keep that in mind. Sometimes I do one-off cuts (like at the miter saw), so I'll be mindful.

Peter

[David L Morse]

Ah. So what I think you're saying is that the 60° degrees on the plate is not the allowable rise above ambient, it's the max temp INCLUDING the ambient temperature. I misunderstood... but that makes a lot more sense.

Well, not exactly. The 60° on the nameplate is the actual measured rise above ambient for that motor design when operated at nameplate ratings. The maximum allowed (for rated insulation life) temperature of the motor windings is given by the insulation class, in this case 120°. Since standard measurement techniques measure the average winding temperature and we need the maximum temperature 10° is added to the average to estimate the temperature of the hottest spot. So, for a 40° ambient the maximum temperature rise for this insulation would be 120°-10°-40° = 70°. Now, according to the nameplate on this particular motor, when we apply 220V at 60Hz to the electrical side and take out 3HP from the mechanical side and allow time for the temperature to stabilize the average winding temperature will be 60° higher than the motor's surroundings. Thus we have a 10° safety margin and going a bit above 40° ambient temperature should not be a concern.

It's like calculating heat loss for you house. You come up with an overall R-factor and use that in combination with the desired inside-outside differential (temperature drop or rise) to get required BTU/Hr. Or you can use a fixed BTU/hr and get the temperature difference from that and the R-factor. At nameplate rating conditions the motor is putting out a fixed amount of heat so that BTU/hr and the motors R-factor determine the temperature rise.

Now for full disclosure I need to say that I have never seen any specifications from Taiwan for the content of their nameplates or how they rate their motors. I am ASSUMING that since they export nearly everything they would have some alignment with the specs of the countries they ship to. The two biggest assumptions here are that their rated default ambient is 40°C and that "HEAT" really means "Temperature Rise". Oh, also of course that Class E insulation is referring to IEC standards.

[Jim Dwight]

Monitoring the temperature is a good idea but I would think all the air moving through the cyclone will keep the ambient temperature in the closet down. It will go up some due to the motor but I doubt it will be a problem. If you were running the motor without air moving through the space, that would be an issue (potentially). (I realize the air moving through will not contact the motor but it will touch the metal fan connected to the motor so it will help absorb any temperature rise)

[Peter Aeschliman]

Jim,

In my case, I'm going to exhaust the dust collector to the outdoors... so I'm not expecting much air movement, aside from the fan-cooling of the TEFC motor. Is that the air movement you're referring to? Or were you picturing me exhausting the dust collector through filters in the closet?

[Peter Aeschliman]

BTW, thanks again David for educating me on this. I'm a bit dense sometimes. :)

[Jim Dwight]

Jim,

In my case, I'm going to exhaust the dust collector to the outdoors... so I'm not expecting much air movement, aside from the fan-cooling of the TEFC motor. Is that the air movement you're referring to? Or were you picturing me exhausting the dust collector through filters in the closet?

Peter,

While the air around the motor will not be moving much if at all, my point is that the motor is directly connected to the blower which has a lot of air going through it. If the motor heats up, the conduction to the blower will be good (metal to metal contact) and the air being blown outside will be heated slightly by blower. This is a cooling path for the motor that I think will be pretty effective.

Jim

[David L Morse]

Peter,

While the air around the motor will not be moving much if at all, my point is that the motor is directly connected to the blower which has a lot of air going through it. If the motor heats up, the conduction to the blower will be good (metal to metal contact) and the air being blown outside will be heated slightly by blower. This is a cooling path for the motor that I think will be pretty effective.

Jim


Jim, that's a TEFC motor like is used on nearly all dust collectors. If the conduction through the fan housing were an adequate cooling method there would be no need for the fan on the back of the motor and you could use a TENV motor. It's the air forced across the motor frame that provides the cooling. I really don't think that you can count much on conduction to the sheet metal fan housing.