Will my VFD overheat in a closed box?

[CONTROL FREQ]

If the user never turns it off the snap switch was pointless, and there is no increased efficiency. Automatic, maybe via thermostat, control when it is needed is going to be most efficient.

Sorry... trade term. when i said "snap switch", i was referring to a thermostatic switch similar to what one might fine on a boiler. They're about 10 bucks, the "good" vortex cooler is about $75 and if you don't have a solenoid valve just lying around somewhere--- i'd suggest if you know enough to talk to people on this site, you should get a better employer (or just buy a sol. valve for 50 bucks... either way, you'll be fine.

 

[milemaker13]

These days, I'm very happy to have the employer I do. If I can save some money for the company by exploring several options that include stock on hand, I will do that. This company spends plenty of money, I can assure you, but personally, I beleive every penny counts. If I need a part, I can buy a part. Thanks.

 

[petersonra]

I am installing a 5 hp fan using a VFD. The book says it will operate up to 131*F. Our plant is warm, around 80*. I want to mount this VFD inside a closed box to avoid dust, damage, ect. The VFD has cooling fins and a small fan.

Do you think this could raise the temp inside the box enough to be an issue? Would I need to ventilate the box? Or better to just mount the VFD to the wall, instead of inside a box?

IMO, 80 degrees F is not all that warm.

There are charts in the Hoffman catalog and software you can download from their web site that will help you determine how warm it will get inside the box.

I will suggest this as well. A small fan inside a sealed enclosure can work wonders if the ambient temperature outside the enclosure is not especially high. Many VFDs already have such a fan.

 

[Jraef]

If you REALLY want to be accurate about the enclosure size and have the wherewithall to navigate Hoffman's website, then you can do this:

Get to the software that picks out an air conditioner and/or heat exchanger for you. Load in the ambient heat parameters and the rejection from the VFD, figure that a VFD is about 97% efficient at full output power, which is your worst case. So if your motor is 3HP, that is 2.24kW, so 3% of that is 67W of heat rejection. Start with a basic box size that will hold the VFD and if it tells you that you need an air conditioner or heat exchanger, keep increasing the box dimensions until it says you no longer need one.

 

[T.M.Haja Sahib]

If your VFD is provided with integral cooling fan,it may not operate properly in a box,unless specifically designed for that purpose.Better check with the manufacturer on this.

 

[Besoeker]

If your VFD is provided with integral cooling fan,it may not operate properly in a box,unless specifically designed for that purpose.Better check with the manufacturer on this.

It may overheat whether or not it has an integral cooling fan. Actually, that has very little to do with it.
The VSD or any equipment that dissipates heat will run warmer than in free air.
The amount of heat, surface area of the box available for cooling and its finish will determine how much warmer.

An example of how I do this gives an idea of scale for painted steel and a 10degC (18F) rise:

I've excluded the back and the bottom. A box of that size would be floor mounting and probably up against a wall. If it's in a corner, one of the sides would also have to be excluded.
If it is going to be mounted outside per the OP, it is likely to have to be stainless steel and that has a lower value of k so will dissipate even less heat for that rise.

 

[T.M.Haja Sahib]

It may overheat whether or not it has an integral cooling fan. Actually, that has very little to do with it.
The VSD or any equipment that dissipates heat will run warmer than in free air.
The amount of heat, surface area of the box available for cooling and its finish will determine how much warmer.

An example of how I do this gives an idea of scale for painted steel and a 10degC (18F) rise:

I've excluded the back and the bottom. A box of that size would be floor mounting and probably up against a wall. If it's in a corner, one of the sides would also have to be excluded.
If it is going to be mounted outside per the OP, it is likely to have to be stainless steel and that has a lower value of k so will dissipate even less heat for that rise.

One critical factor seems to be missing:number of air changes required to maintain that temperature rise.

 

[Besoeker]

One critical factor seems to be missing:number of air changes required to maintain that temperature rise.

If it's a closed box, there won't be any air changes.

 

[T.M.Haja Sahib]

If it's a closed box, there won't be any air changes.

Then how that temp rise of 10 deg C (18F) would be maintained?

 

[Besoeker]

Then how that temp rise of 10 deg C (18F) would be maintained?

Didn't you read the table heading?
"Surface heat dissipation."
It's an entirely different calculation for ventilated enclosures.

 

[T.M.Haja Sahib]

Didn't you read the table heading?
"Surface heat dissipation."
It's an entirely different calculation for ventilated enclosures.

Ventilated enclosure means it requires a definite number of air changes per hour to maintain its inside temperature.Is yours a ventilated enclosure?If not how its temperature is maintained?Using air-conditioners,for example?

 

[milemaker13]

We put two cooling fans in the box, along with two exhaust openings. This is probably overkill, but thats fine. I don't see having any heat issues anymore. Thanks for the help!

 

[Besoeker]

Ventilated enclosure means it requires a definite number of air changes per hour to maintain its inside temperature.

Not really.
The required airflow depends on the heat to be dissipated and preventing the internal temperature exceeding acceptable limits.
The the heat to be dissipated is very little, it might not any air changes at all.

Is yours a ventilated enclosure?If not how its temperature is maintained?Using air-conditioners,for example?

It's not my enclosure.

 

[T.M.Haja Sahib]

We put two cooling fans in the box, along with two exhaust openings. This is probably overkill, but thats fine. I don't see having any heat issues anymore. Thanks for the help!

How you use your cooling fans is also important to minimise dust problems to your box.......

 

[Besoeker]

We put two cooling fans in the box, along with two exhaust openings. This is probably overkill, but thats fine. I

Depends on the fan size. I estimate that you'd need about 40 cfm.
A fairly small fan will do that but some are lower than that.

 

[Jraef]

Aaaaaand here we go...

I predict no less than 50 posts to this thread now, even though the OP seems to be satisfied...

 

[Besoeker]

Aaaaaand here we go...

I predict no less than 50 posts to this thread now, even though the OP seems to be satisfied...

I thought my information on the 40 cfm relevant and possibly helpful information. There are panel fans that deliver less than half that.

 

[milemaker13]

Each fan we used puts out 36 cfm, so that is 72 cfm total. We are using simple foam filters and have the fans arranged so they blow into the cabinet, creating positive pressure to prevent dust being pulled in around conduit openings, ect.

I don't expect any major problems from dust. Maybe an occasianal blow out of the cabinite.

 

[Jraef]

I thought my information on the 40 cfm relevant and possibly helpful information.

It was.

Not what I meant.

 

[Besoeker]

Each fan we used puts out 36 cfm, so that is 72 cfm total. We are using simple foam filters and have the fans arranged so they blow into the cabinet, creating positive pressure to prevent dust being pulled in around conduit openings, ect.

I don't expect any major problems from dust. Maybe an occasianal blow out of the cabinite.

Sounds fine. Just bear in mind that the fan flow will be impeded some by the filters.
So maybe fine plus not a lot.