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Thread: Electrical room ventilation.

  1. #1
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    Electrical room ventilation.

    Is there any requirements in the NEC about electrical rooms with heat generating equipment (transformers) needing a supply and return air vent? I have come across a very warm room that has two vents with fire dampers, but they only vent into the attic space in the hallway. There is no supply air flow at all. This is a new facility and pretty much all the other electrical rooms have duct work tied to air handlers. General contractor says it way designed that way. I think this is bologna.....

  2. #2
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    Re: Electrical room ventilation.

    I would say that you'd just have to apply the ambient corrections at the bottom of table 310.16, but I'm not sure how the panels tie into the equation. :confused:

    408 seems quiet regarding ambients.

    Edit to add: Breakers are rated at 40°C ambient temperature, what is the ambient in this room?

    [ March 15, 2005, 11:26 PM: Message edited by: georgestolz ]

  3. #3
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    Re: Electrical room ventilation.

    The NEC requires ventilation to vent full load heat loss. No requirement as to where that heat is suppsed to go. 450.9

    some xfmr manufacturers have provided guidelines as to the size of a exhaust and make up air vent in their instructions.

    I usually ask the mechanical engineer to address it when in plan check
    I'm an Inspector, what do I know?

  4. #4
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    Mar 2004
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    Re: Electrical room ventilation.

    This is a common problem. Lots of times a ventilation fan or louver just won't cut it. What I have told owners is that as long as there is nothing besides panels and xformers in the space, 100 degree room is not going to harm anything. However, if any electronics are in the space, (e.g. TVSS, fire alarm panel, etc) then there is a real issue.

    Personally I try to put dry types outside. This eliminates the noise, heat, emag issues and makes for more space in the electrical rooms. However, some do not find them as attractive on the outside of the building as I do.

    If the dry type must be inside, I ask the mechanical to condition the space. But a 97% percent efficient 112 KVA xfmr is a big load for an AC. Also you have to design it so that the HVAC doesn't dump heat into the elec room in the winter. This pretty much means a dedicated unit. Now that outside xfmr doesn't look so ugly....
    "In this house, we obey the laws of thermodynamics" - H. Simpson.

  5. #5
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    Re: Electrical room ventilation.

    Originally posted by sceepe:
    Personally I try to put dry types outside. This eliminates the noise, heat, emag issues and makes for more space in the electrical rooms.
    I am not criticizing here just curious what type of buildings you work on that you can be putting transformers outside.

    I spend a lot of my time in office buildings and they will not accept transformers outside.

    Most times we have to hang them from the ceiling which can be a project with weights from about 300 to 900 lbs.

  6. #6
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    Re: Electrical room ventilation.

    Hmm...I must have been tired. I saw electrical room and missed the transformers sitting in it.

  7. #7
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    Re: Electrical room ventilation.

    Add some lava rocks on top of the transformer, add a little water from time to time, and you get to work in your own personal sauna!!

    That's one of your new free health benefits!!

    Steve

  8. #8
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    Feb 2003
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    Re: Electrical room ventilation.

    Miles,
    How would you figure the heat gain from a 112 kva transformer @ 97 percent efficiency? would this be right?

    112 kva X 1000 = 112000 watts divided by 100 percent X 3 percent transformer loss. = 3360 watts X 3.1414 watts to btu conversion. this would give you a BTU gain of 10,555 BTU. this would be at full load

  9. #9
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    Texas
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    Re: Electrical room ventilation.

    The British power unit for thermal energy is "BTU per hour".

    The conversion rate for Watts is 3.4144 (you used 3.141) so you get 11472 BTU/Hour.

    This is 0.955 refrigeration ton. (A truly peculiar unit in a system of peculiar units.)

    So you need a ton of A/C to cool this, with a reasonable EER you can do it for about another kilowatt.

    That outside transformer looks real pretty right now.

  10. #10
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    Jun 2003
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    Re: Electrical room ventilation.

    An energy star transformer would have to be almost twice that efficient, so you could almost cut your cooling load in half. And a transformer would seldom be fully loaded. According to Square D, 35% loading is the average.

    So the 1 ton would probably be more like 1/4 to 1/6th of a ton.

    energy star transformer requirements

    Steve

    Edited to add "almost". I was reading the single phase chart.

    [ March 16, 2005, 01:54 PM: Message edited by: steve66 ]

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