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Thread: Building presdure.

  1. #1
    Join Date
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    Building presdure.

    So, oversized RTU. 40 ton Voyager 3. (2 of them)
    On 4 story office, VAV supply's (which I just calibrated via flowhood and set design cfm again on this 20 year old building) and open return on each floor.
    Single space pressure sensor on top or bottom floor. I cant recall.
    Original design was for 30 rtus. Minimum load is about 10 ton.
    Present units have 15 ton and 25 ton scroll compressors. Previous units had semis with 6 total stages via unloaders. ( I had still added accumulators to those due to floodback.)
    Power exhaust with full speed fans (2 each) and modulating exhaust dampers based on fresh air damper acctuator position.
    Question...wouldnt it be better to have the space pressure sensor averaging all 4 floors?
    60 tons was too big...80 tons is outrageous. So the fans swing the building pressure a lot.
    I thought to disconnect 2 fans , or maybe 3 of 4. I would disconnect 1 units exhaust fans entirely to stop them "arguing" with each other. What do you think?
    I also will have to increase VAV cfm wherever I can due to lack of load.
    I guess we I stalled these about 4 years ago. Ouch.
    Any input very welcome. ( I have to tread carefully since this company installed this.)

    Sent from my SM-G950U using Tapatalk

  2. #2
    Join Date
    May 2009
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    Single point inside reference against your redbird will work fine. As long as you share the inside reference between the units , and they have the same adjustable setpoint.

    If that doesn't work, and you have a BAS, take the Voyagers out of the pressure control equation by using a separate controller to control building pressure. One input, one setpoint, and a shared output to the damper sets on each unit.

    If the unit fans are waay oversized, you might also try slowing down all of the control loops just a little bit to lessen the chance for hunting.

  3. #3
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    vfd on voyager supply fans like intellipaks?
    Keep it simple to keep it cool!

  4. #4
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    To justify changes without compromising your company tell the owner the new suggestions are the result of an ongoing quality assurance program that is based partly on state of the art technology. It looks like to me that is true. I would not control the exhaust fans based on any damper position. It is far better to use results instead of probability.
    No man can be both ignorant and free.
    Thomas Jefferson

  5. #5
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    icy78,
    The way I finally decided how to resolve (or address) this type of issue (Building Pressure) was to ask myself "Where does the problem manifest itself" ?
    What I mean by that is where does the problem show up ? The entry doors, right ? Either they are standing open (high pressure) or they are difficult or impossible to open (low or negative pressure).

    With that in mind I would make my interior reference location on the ground floor in a common area communicating with all or most of the entry spaces. This would be the "High Pressure" port.
    If possible, control 1 Exhaust Damper (not fan) to maintain a pressure setpoint (0.05" WC) and then slave the other Dampers from that signal. Of course you would need interlock logic to only allow operating units/Dampers in this scenario.

    I hope I'm understanding the situation correctly.
    Last edited by Cagey57; 04-15-2021 at 03:15 PM. Reason: 2nd thought
    If sense were so common everyone would have it !
    You cannot protect the Stupid from themselves !
    "Experience is the ability to recognize a mistake Before you make it again!" (Stolen Quote)

  6. #6
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    Thread Starter
    Quote Originally Posted by Cagey57 View Post
    icy78,
    The way I finally decided how to resolve (or address) this type of issue (Building Pressure) was to ask myself "Where does the problem manifest itself" ?
    What I mean by that is where does the problem show up ? The entry doors, right ? Either they are standing open (high pressure) or they are difficult or impossible to open (low or negative pressure).

    With that in mind I would make my interior reference location on the ground floor in a common area communicating with all or most of the entry spaces. This would be the "High Pressure" port.
    If possible, control 1 Exhaust Damper (not fan) to maintain a pressure setpoint (0.05" WC) and then slave the other Dampers from that signal. Of course you would need interlock logic to only allow operating units/Dampers in this scenario.

    I hope I'm understanding the situation correctly.
    I like that thought about "where does the problem manifest itself"?
    It is the first floor, which has doors to the factory and vestubiled doors to outside.
    Hey! Maybe the outside pressure sensing or should be in the factory area. I mean, that the problem area. So currently it's looking at outside to building....but the doors to the factory are the real issue, so that's where the outside reference should be?
    Hmmm I'm almost saying duh to myself

    Sent from my SM-G950U using Tapatalk

  7. Likes Cagey57, heatingman liked this post.

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