Case fan for VFD in enclosure ??

Status
Not open for further replies.

brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
I installed a VFD last week for a 20HP submersible pump last week outdoors on a pole next to the pump. I went back and forth with my supplier about making sure we had an enclosure large enough that heat wouldn't be an issue and asked for case fans. The sales rep for the VFD recommended a 20x20x8 enclosure with a pair of 6" louvers and said we wouldn't have any issues. Now it's shutting down throwing an overheat alarm.

Supplier went back to the sales rep, and they are suggesting another pair of louvers to cut in, and are offering 4" 120v case fans for $320/ea. That's seems really high. I've already got $400 in the enclosure; add the louvers and two of their fans and it'll end up costing $1100.

You guys have any other leads on case fans that aren't as expensive ? I did a google search before leaving the office yesterday and found some that were pretty cheap but were made for PC cases.


Sent from my iPhone using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Pfannenberg

By the way. The sales guy screwed you over once already now he's going to do it again. What you really need to do is run the numbers and see how much airflow you need to keep the enclosure cool enough. It really doesn't matter how big it is for the most part. The other thing is if it's outside solar gain may be an issue and it may be advisable to insulate it.

Before I would buy anything else from this clown I would demand to see the calculations that he used to determine that the louvers he sold you in the first place were adequate. I would also demand to see the calculation used to determine the new louvers and fans required. It's not like this is really hard to come up with there's plenty of places on the internet with thermal calculations.
 

brantmacga

Señor Member
Location
Georgia
Occupation
Former Child
Thanks I appreciate the input ..... I think they just used the clearance dimensions listed in the manual, and this inclosure is double that on top and bottom, and about 4 times on the side. Need more airflow though.


Sent from my iPhone using Tapatalk
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Thanks I appreciate the input ..... I think they just used the clearance dimensions listed in the manual, and this inclosure is double that on top and bottom, and about 4 times on the side. Need more airflow though.


Sent from my iPhone using Tapatalk


+1 on the previous comments, this supplier is using gross rules of thumb that may or may not apply. One of those that floats around a lot is that if you take the size of the manufacturer's NEMA 1 enclosure and quadruple the VOLUME of a NEMA 4 it will provide enough surface area to dissipate the heat rejection of the VFD. I have found that to work at 20A and below (10HP 480V or 5HP 240V), but only with INDOOR spaces that are climate controlled, i.e. food processing facilities that need wash down enclosures, but are generally cool ambient. I have NEVER seen that work outdoors and if the sun hits it, as Bob said the solar heat gain kills just about any option besides an A/C unit.

Many cheap drives are rated for 40C operation (104F), some are rated for 50C (122F) but may require de-rating, a few can go to 60C (140F) with de-rating and a small few are capable of 70C (158F) with de-rating and auxiliary PC board cooling fans. If you have one of the 40C drives, it's no wonder that it's tripping on OT.

Ventilation makes a difference, but fans only? I would never recommend it. Air flow introduces two enemies of electronics; moisture and dirt. Some drives have conformal coated PC boards which helps, but the moisture can still collect on pins and sockets where things plug together and cause failures, and those connections can't be coated. So if you add vents, you must add filters to collect the dust and condense some of the moisture, then have weep holes for the moisture to escape, and someone must change the filters periodically without forgetting. People that know what they are doing will often design in baffles for the air to flow so that moisture from rain, fog etc condenses in the baffles and drips out rather than going into the drive. But as you might imagine, this becomes a highly specialized and engineered enclosure package.

Throwing a couple of louvers on the box was a cruel joke, but you can't just add fans to this without causing more problems than what you solve.
 

kwired

Electron manager
Location
NE Nebraska
With louvers only, you at least need one low and one high to allow natural convection to be better utilized.

If it is outdoors direct sunlight hitting the enclosure is probably your biggest killer.

I once saw an outdoor situation similar to yours where they cut out the back of the enclosure and the heat sink (base of drive) was outside the enclosure with the rest of the drive inside the enclosure. I believe that one was fabricated by a panel shop and not just some "in the field" contraption though.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
With louvers only, you at least need one low and one high to allow natural convection to be better utilized.

If it is outdoors direct sunlight hitting the enclosure is probably your biggest killer.

I once saw an outdoor situation similar to yours where they cut out the back of the enclosure and the heat sink (base of drive) was outside the enclosure with the rest of the drive inside the enclosure. I believe that one was fabricated by a panel shop and not just some "in the field" contraption though.

Yes but the drive must be designed for that, it's called a "flange mount" option; you can't just rig up some brackets for a regular drive. It's a great idea though because the heat sinks out the back avoids most of the drive's heat rejection to go out of the enclosure. But still, if the sun hits those heat sinks it works exactly the opposite way and can heat up the transistors. One new thing I ran into with that last year though was wasps using the heat sink fins as a cozy warm little nesting place. Blocked the air flow and the drive was tripping on OT.
 

tom baker

First Chief Moderator
Staff member
I used to install the fan (for this type of application) as an exhaust fan, but its much more efficient to have supply fan that pressurizes the enclosure, as the cooler outside air is less dense, more flow, and cooler air. Put the exhaust high and supply low

This is not commonly done as the its easier to have a filter on the air intake, and put the exhaust fan on the inside


A good source of information is https://www.pfannenbergusa.com/filterfan
Phannenberg has a filter fan that is made for what I mentioned above
 

kwired

Electron manager
Location
NE Nebraska
I used to install the fan (for this type of application) as an exhaust fan, but its much more efficient to have supply fan that pressurizes the enclosure, as the cooler outside air is less dense, more flow, and cooler air. Put the exhaust high and supply low

Not so sure it is that simple. Cooler air should have more density, should also take more energy to move the extra matter, but at same time you won't need as much flow with cool air as you need with warmer air.

Then you also have inlet/outlet size compared to how much volume the fan is trying to move, which effects static pressure inside.

Fan on inlet would normally result in positive pressure inside, fan on outlet would normally result in negative pressure inside. Positive pressure would be more density then negative pressure....I won't claim to be know a lot about how to calculate all this, but there are a lot of things that can effect the overall performance and you have to find what works for the application.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The change in density with pressure is, IMHO, insignificant at those pressures.
But the change in density with temperature could indeed affect the mass flow output of a constant speed fan.
Changes simply in the volume moved with the same mass flow will not affect the cooling much either.

Sent from my XT1585 using Tapatalk
 

Besoeker

Senior Member
Location
UK
Thanks I appreciate the input ..... I think they just used the clearance dimensions listed in the manual, and this inclosure is double that on top and bottom, and about 4 times on the side. Need more airflow though.


Sent from my iPhone using Tapatalk
Did you get my email?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Using an exhaust fan or a supply fan does not matter one iota as far as cooling the enclosure. The same amount of air coming into the enclosure is required regardless of the slight pressure differences at the fan. It's generally considered good design practice to put the fan on the cool side so the fan last longer.

The problem with an outdoor system with a fan is that it sucks dust in. This is not so bad with louvers but when you start deliberately sucking the dust in it can be a huge problem. Your best bet is at the very least to put a fairly fine screen at the inlet to keep out as much of the Dust and insects as you can. On several occasions I have had a sheet metal Place fabricate an upside down hood with screen at the bottom that bolts onto the bottom of an enclosure. A similar Hood but one that is u-shaped is bolted to the top of the enclosure. Then the top of the enclosure is cut out almost entirely and fans are installed in the bottom of the enclosure. This works pretty well of course isn't perfect. But it does keep out most of the Dust and most moisture. You can try putting some kind of filter on the inlet to remove more dust but that requires people to go out and clean them periodically and they generally won't do it.

Incidentally, one thing you might want to consider trying is adding a fan on the inside of the enclosure to blow air onto the heat sink of the vfd. Sometimes that's all it takes.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Why didn't you go for outdoor rated system like this that is made to have outdoor airflow through heat rejecting parts?
https://www.saidrives.com/support-downloads/brochures/24-sai-drive-dura-drive-packaged-vfd/file

A combination of dust, fog mist, and temperature swing will cause conductive film on the parts exposed to the outdoor air. If the equipment is not rated for it, you are likely to run into problems sooner than you want.

Exactly. It pays to isolate the air inside the enclosure as much as possible from the outside. I've used IceQube's cabinet AC units on several recent outdoor projects, and have been impressed with their build quality and customer service every time.

I've used the MM series with good results:

http://www.iceqube.com/air-conditioners/qube-series-mm/

They're efficient and will run only when needed. They're relatively cheap too.



SceneryDriver
 

Ingenieur

Senior Member
Location
Earth
Hoffman makes kits https://s3-us-west-2.amazonaws.com/pik-images/MFGSpec-IND1015.pdf
fan, filter/vent and t-stat
put one each on the existing vent cutouts
fan upper to take advantage of natural convection, fan draws thru enclosure, not blowing in

Basic vent equation
fan cfm = 3.3 x (P / delta T)
3.3 is the vol of air required at sea level per deg F to allow one W-min of heat transfer
P heat in W to get rid of, ~2.5% of inverter rating
temp difference between outside max temp - operating temp

as others noted enclosure size is not a factor

assume 15 kw drive so waste is 375 W
max oa temp 80
Equip operating temp 104
Delta T = 104 - 80 = 24
fan cfm = 3.3 x (375/24) = 52 cfm
add 5% for every 1000' asl
at 5000' asl cfm = 5 x 0.5 x 52 = 65 cfm
select next higher std size

note: if oa temp ~ equip rating you need mechanical cooling
you need to match enclosure rating, eg, NEMA 3, etc
you may need a sun shade/shield
 
Last edited:

tom baker

First Chief Moderator
Staff member
The problem with an outdoor system with a fan is that it sucks dust in. This is not so bad with louvers but when you start deliberately sucking the dust in it can be a huge problem..

Pfannenberg makes a fan with a built in filter. Their web site has very good information about enclosure cooling.
A good source of information is https://www.pfannenbergusa.com/filterfan
 

Besoeker

Senior Member
Location
UK
Hoffman makes kits https://s3-us-west-2.amazonaws.com/pik-images/MFGSpec-IND1015.pdf
fan, filter/vent and t-stat
put one each on the existing vent cutouts
fan upper to take advantage of natural convection, fan draws thru enclosure, not blowing in

Basic vent equation
fan cfm = 3.3 x (P / delta T)
3.3 is the vol of air required at sea level per deg F to allow one W-min of heat transfer
P heat in W to get rid of, ~2.5% of inverter rating
temp difference between outside max temp - operating temp

as others noted enclosure size is not a factor

assume 15 kw drive so waste is 375 W
max oa temp 80
Equip operating temp 104
Delta T = 104 - 80 = 24
fan cfm = 3.3 x (375/24) = 52 cfm
add 5% for every 1000' asl
at 5000' asl cfm = 5 x 0.5 x 52 = 65 cfm
select next higher std size

note: if oa temp ~ equip rating you need mechanical cooling
you need to match enclosure rating, eg, NEMA 3, etc
you may need a sun shade/shield
Would you like to have a copy of the spread sheets I offered?
If so, PM me with an email addy.
 

kwired

Electron manager
Location
NE Nebraska
Using an exhaust fan or a supply fan does not matter one iota as far as cooling the enclosure. The same amount of air coming into the enclosure is required regardless of the slight pressure differences at the fan. It's generally considered good design practice to put the fan on the cool side so the fan last longer.

The problem with an outdoor system with a fan is that it sucks dust in. This is not so bad with louvers but when you start deliberately sucking the dust in it can be a huge problem. Your best bet is at the very least to put a fairly fine screen at the inlet to keep out as much of the Dust and insects as you can. On several occasions I have had a sheet metal Place fabricate an upside down hood with screen at the bottom that bolts onto the bottom of an enclosure. A similar Hood but one that is u-shaped is bolted to the top of the enclosure. Then the top of the enclosure is cut out almost entirely and fans are installed in the bottom of the enclosure. This works pretty well of course isn't perfect. But it does keep out most of the Dust and most moisture. You can try putting some kind of filter on the inlet to remove more dust but that requires people to go out and clean them periodically and they generally won't do it.

Incidentally, one thing you might want to consider trying is adding a fan on the inside of the enclosure to blow air onto the heat sink of the vfd. Sometimes that's all it takes.
A lot drives will already have a fan that moves air over the heat sink.

Seems like most environments I work around will have a significant amount of dust, most of them probably would be Class 2 hazardous locations but being outdoors lowers them to non classified areas, there is still a lot of dust at times though and anything in the vicinity with a forced air inlet is taking in some of that dust. I'm talking mostly grain and feed handling equipment. Some of it only gets used once a year for a couple weeks but is really dusty when it is in operation.
 
Status
Not open for further replies.
Top