Facility AC to Electrical Enclosures

[Emily Beck]

Are there any code requirements for duct work installed into an electrical enclosure for facility AC cooling (vs. a dedicated air conditioner)?

 

[petersonra]

I don't think there are any NEC requirements.

I would point out that I don't see anyway that you could UL508a label such a contraption though. Maybe as a type 1 enclosure.

You might also have some condensation issues unless you were careful how you handled it.

Why is it that someone came up with such an idea?

 

[retirede]

One possible issue I see is temperature control.
If the chiller is controlled by thermostat(s) in the facility, could you have problems with the cabinet overheating for example on a cool day when the AC requirements for the facility are minimal? Or in the winter when the building is heated and the AC is not even running.

No NEC issue afaik.

 

[petersonra]

One possible issue I see is temperature control.
If the chiller is controlled by thermostat(s) in the facility, could you have problems with the cabinet overheating for example on a cool day when the AC requirements for the facility are minimal? Or in the winter when the building is heated and the AC is not even running.

No NEC issue afaik.

you would have to run insulated trunks for supply and return plus put a damper with thermostat on each cabinet.

the thing is that most cabinet air conditioners don't need to run much more than a few hours a day, if that. but they have to be designed to handle worst case.

I think when someone does the calculations and discovers how much cool air it will take to do this they are going to get a big surprise as to how big the duct work will end up being.

It is hard to know what is practical since the OP gave so little information, but the question asked is fairly straightforward to answer.

The thing that might make such a scheme worthwhile is the labor savings. A lot of places that use cabinet air conditioners end up having to service the filters once or twice a month because of the dust in the plant. that labor can get really pricey over time. i have seen places where they do it every week. if it is a union plant, probably operators are not allowed to do this kind of work so it has to be done by an electrician. can end up costing $200 to go out and vacuum the filter.

 

[StarCat]

Control Cabinet Cooling

Control Cabinet Cooling

Electrical and Control cabinets can be a tricky matter with repsect to " Septoint Control " as they do not behave like a typical load, and as thus using a thermostat in what could be called a typical manner can get you into trouble. This is especially true if you have a hot control cabinet, A DX cooling system, and you put the thermostat right in the cabinet. This can create a situation where the evaporator runs too cold, and you get to floodback and destroy a compressor.
I responded to a dead unit at an industrial facility where this was exactly the case.
In this instance I set the new system up for " Return air control " but Supply air control or other strategies can work depending on how things are set up.
The goal is to insure that the system is properly loaded in a case like this and also that you are getting good air and temp distribution into the conditioned space.
This is why having the thermostat control mounted right near a hot bus is nto a good idea. You need averaging techniques.
What I am describing is pertinent to a single DX cooling arrangement, but if I were running off a supply duct from a larger system, I would likely say using return air control is where I would start. The trick there is you almost need a face and bypass damper in such a case as I would always want positive airflow through the cabinet.

 

[petersonra]

One of the reasons I am not overjoyed with such an idea is some of the issues you raise. However if you are only diverting a small amount of the cool air to cool cabinets it should not be much of an issue.

If you have chilled water available, there are cabinet coolers that can be purchased that use chilled water.

 

[Andy Delle]

It's done in data centers all the time. The raised flooring is used as the supply air plenum and enclosed racks are cooled by air pressure up through them. In other areas they just put in perforated floor panels where you want air. That system works well and has been widely used for they past 50 years. Another bad idea I have seen done in a few television facilities is a plenum over a group of racks forcing cold air down. This does not work very wells at all since most equipment pulls cool air in the front and discharges hot air from the back or sides. You end up with excessive back pressure on the equipment cooling fans and poor heat removal.

 

[tom baker]

There are also cabinet coolers that use compressed air. And Hoffman has small ac units for control panels, and they may be able to maintain the NEMA panel rating.

 

[petersonra]

It's done in data centers all the time. The raised flooring is used as the supply air plenum and enclosed racks are cooled by air pressure up through them. In other areas they just put in perforated floor panels where you want air. That system works well and has been widely used for they past 50 years. Another bad idea I have seen done in a few television facilities is a plenum over a group of racks forcing cold air down. This does not work very wells at all since most equipment pulls cool air in the front and discharges hot air from the back or sides. You end up with excessive back pressure on the equipment cooling fans and poor heat removal.

data centers have a relatively constant heat output though.

 

[petersonra]

There are also cabinet coolers that use compressed air. And Hoffman has small ac units for control panels, and they may be able to maintain the NEMA panel rating.

vortex coolers are insanely expensive to run. air is a very expensive utility. there is also often water or oil in the compressed air that makes a big mess inside the control cabinet over time. however, if you have a source of clean, dry air close by and it does not need to run much or you can tolerate the expense, vortex coolers can be a good option. they also have the advantage of no moving parts.

there are a bunch of companies making cabinet air conditioners. they are commonly available in type 12 and type 4X as far as enclosure ratings go.

personally, I have been trying to eliminate cabinet air conditioners. they are expensive and require a fair amount of service. and longevity can be an issue. many times i can avoid needing a/c in a cabinet by proper ventilation or by not putting the heat in the cabinet in the first place. most of the cabinets that I design that generate a lot of heat are because of large vfds. I can get vfds that have the heat sink mounted out the back of the cabinet so most of the heat is expelled outside the cabinet. these days there are fans available with grills that are rated as type 12 so it is often possible even in a type 12 environment to remove the heat just with fan forced ventilation. however, fans have a limited life time and also require service to clean the filters. I usually put them on a thermostat to reduce the run time.

 

[retirede]

This is all good, but the first sentence in post #2 answered the OP’s question.

 

[petersonra]

This is all good, but the first sentence in post #2 answered the OP’s question.

but you know how much we all love to answer unasked questions.

 

[retirede]

but you know how much we all love to answer unasked questions.

Yeah, since she is a new member, I hope she is not put off by our SOP.