Installing 12 VFDs in one control cabinet

[wireman]

Several comments:
1) Here is a link to Hoffman/PentAirs panel heat calculator: https://coolingtool.pentairprotect.com/index.html

2) Depending on the HP size of the VFD's, I'd also be concerned about the amount of noise, EMI, EMF, or whatever you want to call it interfering with things, especially if you'll also be installing line reactors or filters inside of the panel too.

3) I've seen panels with large drives be modified so the drives' heat sinks are cut out thru the back of the panel, thus most of the heat is effectively exhausted.

 

[Besoeker]

2) Depending on the HP size of the VFD's, I'd also be concerned about the amount of noise, EMI, EMF, or whatever you want to call it interfering with things, especially if you'll also be installing line reactors or filters inside of the panel too.

According to post #11, it is 73HP in total (about 55kW).

 

[petersonra]

I just ran a heat calc thru the Hoffman calculator last night. It said the inside of the VFD cabinet was going to be 294 degree F without cooling and would need about 12,000 BTU/hr of A/C.

 

[wireman]

I just ran a heat calc thru the Hoffman calculator last night. It said the inside of the VFD cabinet was going to be 294 degree F without cooling and would need about 12,000 BTU/hr of A/C.

Hmm, obviously that is rather warm!! Are you sure the BTU’s or watts are correct and you mix up degrees C or degrees F?

I’ve used that Hoffman calculator a lot and it seem legit.

 

[petersonra]

Hmm, obviously that is rather warm!! Are you sure the BTU’s or watts are correct and you mix up degrees C or degrees F?

I’ve used that Hoffman calculator a lot and it seem legit.

Big drives can put out a lot of heat. That's why I like to run them with the heat sinks out the back of the cabinet if I can

 

[drktmplr12]

I just ran a heat calc thru the Hoffman calculator last night. It said the inside of the VFD cabinet was going to be 294 degree F without cooling and would need about 12,000 BTU/hr of A/C.

12000 BTU to maintain what temperature?

294 F doesnt sound correct. What data input to calculator?

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[Sahib]

Without getting into your A/C sizing issues (assuming you know how that works), it's still important to make sure the clearances are adhered to. I've seen control panels with VFDs in them where everyone ASSumed that because they had A/C units set for 70F, that they could crowd the VFDs in there. But they have been dead wrong, as in lots of dead VFDs, because obstructing the proper air flow resulted in swirls and eddies that allowed specific components to over heat inside of the drives.
Here's an example of a bad VFD panel design, a lot of these drives failed in the field, despite having an A/C unit set at 70F, because the spacing was not observed.

IMO, air conditioning the enclosure appears to be cost effective compared with cooling fans and associated filter cleaning, moisture infiltration etc issues. If proper cooling of VFD's are not achieved with A/C temperature setting of 70F, reduce the temperature setting further.

 

[Besoeker]

IMO, air conditioning the enclosure appears to be cost effective compared with cooling fans and associated filter cleaning, moisture infiltration etc issues. If proper cooling of VFD's are not achieved with A/C temperature setting of 70F, reduce the temperature setting further.

Over the many years we were making variable speed drives, we have used aircon on only a handful and that was we needed better ingress protection than forced air cooling could offer. On the smaller drives, we mostly used door mounted axial fans and filters calculated to provide sufficient air flow to shift the heat generated by the drives. On larger units we used what we referred to a "snail" fans directly blowing on the heatsinks. Snail because of their shape.

We also did a few with the heatsinks out of the back of the panel. These were for dockside use so the enclosures had to be IP55. Also, because of the salt laden atmosphere, the heatsinks couldn't be aluminium, the usual material. We used copper.

 

[Sahib]

Bes: With aircon cooling at suitable temperature setting, VFD's spacing may also be relaxed a bit, IMO. That is another advantage of using aircon cooling.

 

[norcal]

If the A/C condenser coil is in a filthy environment there is going to be problems if no maintenance is done, air flow is everything. Trying to stuff 10 pounds of manure in a 5 pound bag never ends well.

 

[Besoeker]

Bes: With aircon cooling at suitable temperature setting, VFD's spacing may also be relaxed a bit, IMO. That is another advantage of using aircon cooling.

I wouldn't do either.
Actually, we rarely put more than one drive in an enclosure anyway. Most our customers wouldn't allow it.

 

[petersonra]

12000 BTU to maintain what temperature?

294 F doesnt sound correct. What data input to calculator?

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I would have to look it up to be sure and I'm not at work this week so I'm not going to do it. But it was about 4000 watts of heat from the drive and I ran a calculation with 122 degrees Fahrenheit in side the cabinet as the maximum temperature and 122 degrees Fahrenheit outside the cabinet as the maximum temperature because that's what the specs said the maximum outside temperature would be. Obviously the drive would shut off long before it got to 294 degrees inside the cabinet

 

[Besoeker]

I would have to look it up to be sure and I'm not at work this week so I'm not going to do it. But it was about 4000 watts of heat from the drive and I ran a calculation with 122 degrees Fahrenheit in side the cabinet as the maximum temperature and 122 degrees Fahrenheit outside the cabinet as the maximum temperature because that's what the specs said the maximum outside temperature would be. Obviously the drive would shut off long before it got to 294 degrees inside the cabinet

There is about 55kW of drives. I would expect not more than about 5% losses or less than 3kW.

 

[petersonra]

It was a 250 hp drive

 

[Besoeker]

It was a 250 hp drive

The thread was about 12 VFDs in one panel with a total power of 73hp or about 55kW.
Are you referencing something else that wasn't given by the OP?

 

[petersonra]

I was not talking about the original posters system but one I ran on one of mine. You can get a lot of heat with some big drives. Most people cheat on cooling of drives because they know that the primary reason people use a drive in the first place is because it's never going to run at full load. They also know that most loads don't run continuously and it takes awhile for the heat to build up.

 

[Besoeker]

I was not talking about the original posters system but one I ran on one of mine. You can get a lot of heat with some big drives. Most people cheat on cooling of drives because they know that the primary reason people use a drive in the first place is because it's never going to run at full load. They also know that most loads don't run continuously and it takes awhile for the heat to build up.

OK. I just don't recall seeing 250hp mentioned.
I would have allowed a bit over 5kW for that for airflow calculations.

 

[Fallriverbryan]

AC for the cabinet.

The boss already had the heat load calculated by the drive supplier. I forget the exact number but believe it is less than 2 tons of AC. I will update when I see the submittal. The area of install is inside and not hot but quite dusty. I'll have to impress upon the customer the need for consistent maintenance.

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[Sahib]

OK. I just don't recall seeing 250hp mentioned.
I would have allowed a bit over 5kW for that for airflow calculations.

That is a bit over 96% for drive efficiency. But remember drive efficiency depends on load. So a customized design of aircon cooling is required in OP case also.

 

[wireman]

I would have to look it up to be sure and I'm not at work this week so I'm not going to do it. But it was about 4000 watts of heat from the drive and I ran a calculation with 122 degrees Fahrenheit in side the cabinet as the maximum temperature and 122 degrees Fahrenheit outside the cabinet as the maximum temperature because that's what the specs said the maximum outside temperature would be. Obviously the drive would shut off long before it got to 294 degrees inside the cabinet

I believe you need to find the thermal dissipation rating of each drive, normally given in BTU/hr and use it in the heat calculation. Whether you need to use the full amount or not probably depends on if the drive will be running at full load or not.