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  1. #14
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    Answer: you get less total air flow.

    But the net difference is still zero: you cannot pressurize a space without adding more of something to it.

    You put 1000 CFM in through the supply and take 1000 CFM away through the return and the room is at atmospheric pressure.

    To increase the pressure in the room you have to be adding more air than you are taking away. That can only come from air leaks into the return side of the system. Including the OA damper.

    PHM
    --------



    Quote Originally Posted by BBeerme View Post
    Think of this way . . .

    You have a closed loop. Circulating continuos.

    What happens if you put a restriction in the middle ?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

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  3. #15
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    Check for closed fire/smoke dampers in the return duct.

  4. #16
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    Thread Starter
    Well, yes and no.

    The space could be pressurized from the negative in the return without adding anything more to the room.

    But see post #3 for further info.


    Quote Originally Posted by Poodle Head Mikey View Post
    Answer: you get less total air flow.

    But the net difference is still zero: you cannot pressurize a space without adding more of something to it.

    You put 1000 CFM in through the supply and take 1000 CFM away through the return and the room is at atmospheric pressure.

    To increase the pressure in the room you have to be adding more air than you are taking away. That can only come from air leaks into the return side of the system. Including the OA damper.

    PHM
    --------

  5. #17
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    Thread Starter
    Pretty sure there is no fire dampers in ducting. Didn't even see balancing dampers in the supplys.


    Quote Originally Posted by WAYNE3298 View Post
    Check for closed fire/smoke dampers in the return duct.

  6. #18
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    Use say if the return was ducked it would not be possible but, in your case it does make sense.

    Sent from my SM-S320VL using Tapatalk

  7. #19
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    If you have a fire wall there should be fire/smoke dampers. Could also be return air restriction. I had a call very similar to this and all the fire/smokes were closed. Is there an economizer and a relief damper?

  8. #20
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    No ducting goes through a fire wall.

    Economizer yes, relief dampers no.

    See post #3.


    Quote Originally Posted by WAYNE3298 View Post
    If you have a fire wall there should be fire/smoke dampers. Could also be return air restriction. I had a call very similar to this and all the fire/smokes were closed. Is there an economizer and a relief damper?

  9. #21
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    Feb 2016
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    Read post #3. Makes a lot of sense.

    Google upgraded my system this morning and it is nothing but trouble. Sent them a nasty gram hoping to go back the way it ways.

  10. #22
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    Feb 2004
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    Just to add, a closed damper will still leak. Sometimes a lot depending on the type. Leakage of 10% isn't uncommon. This can be tested using the temperature method if necessary.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

  11. #23
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    Jun 2012
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    So, if you are looking up at the underside of the roof, you can see the unit's curb? If not and there is ducting above the hard ceiling, the RA duct might have been compromised perhaps. If you can see the curb and all the ducting and know that it is intact, the economizer might need some judicious application of some mastic to the damper blades after you de energise the actuator motor... That is provided that you don't need OA for the server room. Easy relief damper is a bit of rubber belting zip screwed at the top over an appropriately sized hole in the SA on the unit... Still amazed that a unit this large and having an economizer does not have a relief damper in it already. Most of my big RTU's have interlocked linkage that work the OA and relief at the same time.

  12. #24
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    Dec 2002
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    And I was thinking server rooms don't have outside air due to pollen, dust , etc damaging the equipment.
    Col 3:23


    questions asked, answers received, ignorance abated

  13. #25
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    May 2014
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    As you can see . . . Questionable 'engineering' and install.

    We can pull in 100% outside air, but no where for it to go.

    Anyone need some extra strut, it's laying all over the place.

    Are glue lams rated for outdoor use? Never seen it before.
    Attached Images Attached Images    

  14. #26
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    Anytime I've seen a package unit on a server room, there has been outside air. Not so much when it is a smaller room served by a mini split.


    Quote Originally Posted by billygoat22 View Post
    And I was thinking server rooms don't have outside air due to pollen, dust , etc damaging the equipment.

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