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VAVs

Discussion in 'Commercial' started by Zman, Dec 5, 2017.

  1. Zman

    Zman Hanging by a Thread

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    1,590
    Location:
    The "I know a Guy" State
    Any good Reads or advice for becoming more familiar with VAVs? I understand the general concept,and they don't seem overly complicated,but what are the more common issues? Dampers, controller, sensors? Do the small holes in the static pressure sensor get plugged? Haven't worked on one yet, but will possibly in the near future.
     
  2. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

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    296
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    Northwest PA
    Hot water reheat, electric reheat, fan powered? type of controls on board independent or building management? Air flow stations set up correctly? Just like any other things in our trade too many options to list to give a general answer to your question.
     
  3. Catpower

    Catpower The Crowd Pleaser

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    in the Cabana
    A VAV box is just that a box with a damper and a motor and controller

    A fan powered terminal is a VAV damper with fan powered heat, hot water, electric, steam, but the names of stuff is different across the country they can be parallel or inline. and there are even systems that use the air handler fan for the heat mode, pretty rare, and they suck pretty bad because the south, east and west sides might need cooling but the north side needs heating, so who wins? The asshole that has the stat in their office

    In the early 00'sI designed and built fan powered terminals that were slick as possum shit, 2- 7.5 KW single fan or combinations of up to 22.5 KW the single fan ones were 12"x12'x18" very quiet and everyone could have their own stat. And they were pretty easily installed by one man, but two did make it easier, at least you didn't have to **** with ceiling grid. After dumping about $100,000 (not counting labor) into it and the UL sticker, a tornado hit the sheet metal shop and took it's roof off, I finally said **** it, I am done, stick a fork in me

    Really it is a very simple operation
     
    Zman likes this.
  4. Rather B Riding

    Rather B Riding Behind bars

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    616
    There as much as a pain in the a... as water source heat pumps. It's right over the top of the bitchy ladies desk.:banghead:

    Really there all a little different. Just know the basics. Interior boxes are cool only the boxes with heat go on the exterior exposed areas. Sorry that's kind of confusing. The heat vavs will be on the perimeter of the building. Heat vavs can be fan powered electric heat or a standard cool vav with a reheat coil on it.
    The ones you can see damper position are much easier. The Trane vavs that the damper is on the treaded rod are a pain in the ass but you can order it as a complete assembly rather than getting the gear the motor and the capacitor. More expensive but it saves time.
    Don't sweat it they're fairly easy.
     
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  5. newtech

    newtech 636

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    Michigan
  6. crackertech

    crackertech assholiness *

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    Fl/IN/Ga/Ms/TX/NJ/VA/NC/TN
    Zman and newtech like this.
  7. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

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    296
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    Northwest PA
    At least when they are over the bitxhy ladies desk you have a good vantage point to look down her blouse. lol see it all goes back to bewbies.
     
    Texas-Tech, Zman and Rather B Riding like this.
  8. newtech

    newtech 636

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    890
    Location:
    Michigan
     
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  9. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

    Messages:
    296
    Location:
    Northwest PA
    I have mostly used a piece of 1/3/8 armaflex
     
  10. otto

    otto Bakery Chef

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    in a van down by the river
  11. HMD

    HMD does it matter?

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    94,439
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    here
    otto likes this.
  12. pintofstout

    pintofstout New Member

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    1,574
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    Olean, NY
    Last edited: Dec 16, 2017
    Zman likes this.
  13. flange

    flange Act like you care and do SOMETHING!!

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    IMT--in my truck
    the two biggest issues we see are design and poor programming. VAV's are generally glorified modulating zone dampers. some have reheat, some are fan powered for various reasons. When these things get programmed, getting it right is important. Things like using the right K factor and actually verifying flows matter. As far as problems with equipment, failed damper actuators if electronic and issues with the pneumatic tubing if wind powered.
    For many years I had a two buildings with 36 VAVs per floor times 41 floors each. Left was all pneumatic, right was all electronic. The pneumatic building had day/night air and summer/winter air. The single biggest issue we had was a tube not being on a port and dragging the pressure down in the mains for day/night or summer/winter.
     
    Zman likes this.
  14. HMD

    HMD does it matter?

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    94,439
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    what kind of stats............ 1 pressure, 2 pressure, 1 stat, 2 stat, r/a, d/a?
    i have something similar. summer winter warmup and i forget the other. 2 stats, 1 d/a, 1 r/a, 3 'trigger' signals, a rats nest of tubing and switching relays above the ceiling at each box. about 1400 boxes.
     
  15. pintofstout

    pintofstout New Member

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    that makes me shudder


    Sent from my iPhone using Tapatalk
     
  16. HMD

    HMD does it matter?

    Messages:
    94,439
    Location:
    here
    yep.
    and get this,,,,,,,, one stat has the branch port epoxied over. uses the stat as a bleed port, thru the velocitrol. confusing as phuck.
    i'll have to draw out the original layout.
    i've been eliminating the rats nest. simplifying with 1 main, 1 da stat, a signal selecter, a regulator, and a switching relay.
    plug all the trigger inputs.
     
  17. crackertech

    crackertech assholiness *

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    Fl/IN/Ga/Ms/TX/NJ/VA/NC/TN
    Sounds like fun
     
  18. flange

    flange Act like you care and do SOMETHING!!

    Messages:
    13,097
    Location:
    IMT--in my truck
    it was a Honeywell job, so reverse acting, and of course lots of relays. also ha three stages of electric heat on perimeter boxes, so three pe switches as well. lots of fun on those over the years when I was with the tools.
     
  19. pintofstout

    pintofstout New Member

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    1,574
    Location:
    Olean, NY
    Yeah I'm all kinds of bummed out of i stumble upon this one. I'd be setting up camp at this job just to understand how it works.

    Such simple theories that wind up so complex in practice- a total complexity far greater then the sum of its parts.


    Sent from my iPhone using Tapatalk
     
  20. Anita sannich

    Anita sannich Exceptionally average

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    562
    Location:
    Spokane WA
    Read the literature that comes with the VAV, I just spent 2 weeks re-doing ductwork another company installed, they neglected to provide 3 feet of straight duct before each damper. Airflow was terrible.