Stacked Transformer Clearances / Ambient Temperature

[Chamuit]

I have a job where I have to install one 45kVA over an existing 75kVA on a unistrut rack. I know stacking is done occasionally. My question is, and I haven't been able to get ahold of the EE, what is the minimum or recommended clearance between the two units to make sure the one doesn't affect the other?

The two manufacturers say don't do it or install a heat shield ( which they cannot describe.)

 

[GoldDigger]

The two manufacturers say don't do it or install a heat shield ( which they cannot describe.)

A "heat shield" would be a slightly misleading term, since it commonly describes something that protects against radiant or conducted heat. In this case it would have to be an air flow control which diverted the heated air rising from the lower transformer to insure that the air flow toward the base of the upper transformer came from unheated ambient air. In the process of doing that, it also must not reduce the free air flow past either transformer.
If they cannot give you guidance, it would take an engineering evaluation to determine what is needed, and that would have to take into account any other structures around the transformers that would affect air flow. These could be above, below or alongside the transformers.
There may be available general studies to use for reference, but I do not know of any.
This sort of question comes up a lot on a smaller scale when analyzing cooling for rack mounted equipment in data centers, etc.

 

[Chamuit]

Answer

Answer

The EE called back and said 6" is all that is required. I wasn't the one to talk to him. I'd like to have asked him a few questions.

 

[MarineTech]

Could you describe the layout of the install? Is it in a closed space? What size room? In free air? On a roof? Where?

In a confined space, I would expect the Engineer to have requested a thermal camera review at high load. For thermal reference temporarily put in some unistrut channel at 6", 12" and 18" above the existing transformer (proposed location of the 2nd transformer).

 

[infinity]

We stack them once in a while without any known problems. Engineers that we deal with are typically silent on spacing.

One such installation where we were told to get them as high as possible:

 

[iwire]

In a confined space, I would expect the Engineer to have requested a thermal camera review at high load. For thermal reference temporarily put in some unistrut channel at 6", 12" and 18" above the existing transformer (proposed location of the 2nd transformer).

You do not work in the real world do you?

 

[Chamuit]

You do not work in the real world do you?

LOL.

 

[Chamuit]

Little more description.

Little more description.

The transformers are in a warehouse, for lack of a better description. There is some ventilation from the swamp cooler on the roof. It does sit by the east roll up doors which get to about 100 even right now in the late morning. I'm thinking in the summer with the doors closed it could easily be 130-150 degrees at the peak of the summer. I built the rack today. I'll try and remember to take a picture tomorrow, when no one is looking.

 

[Chamuit]

A "heat shield" would be a slightly misleading term, since it commonly describes something that protects against radiant or conducted heat. In this case it would have to be an air flow control which diverted the heated air rising from the lower transformer to insure that the air flow toward the base of the upper transformer came from unheated ambient air. In the process of doing that, it also must not reduce the free air flow past either transformer.
If they cannot give you guidance, it would take an engineering evaluation to determine what is needed, and that would have to take into account any other structures around the transformers that would affect air flow. These could be above, below or alongside the transformers.
There may be available general studies to use for reference, but I do not know of any.
This sort of question comes up a lot on a smaller scale when analyzing cooling for rack mounted equipment in data centers, etc.

Thanks.

 

[iwire]

Like Rob, we stack them when we have to and we just maintain at least the clearances listed.

Can I absolutely say that stacking them will not reduce the life span of the upper transformer?

Nope, I am even willing to bet it does shorten the overall life by some very small percentage but that is what happens when the customer cannot find more space for the equipment it takes to do the job.

 

[infinity]

Like Rob, we stack them when we have to and we just maintain at least the clearances listed.

Can I absolutely say that stacking them will not reduce the life span of the upper transformer?

Nope, I am even willing to bet it does shorten the overall life by some very small percentage but that is what happens when the customer cannot find more space for the equipment it takes to do the job.

Perfect answer. If there is a small trade off of shorter life span it's still has a benefit of saving space or simply making an impossible installation possible.

 

[MarineTech]

You do not work in the real world do you?

Okay, specifically what was not real world about my suggestion?