Barometric by-pass with variable airhandler
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  1. #1
    Join Date
    Jan 2004
    Posts
    60

    Barometric by-pass with variable airhandler

    Originally had zoning system installed with barometric bypass on the single speed air handler, now after replacing it wit variable speed one i have a question about need of the bypass. Sometimes I notice drive and bypass is fighting each other and I end up with fully open bypass and full speed running air handler with on zone open.
    Little background: 3-zone system all equal sizes total airflow set on 1000/750cfm hi and lo.
    So do I need a bypass? What is downside?

  2. #2
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    What's the max static pressure for your air handler? Hold the bypass closed - Run at stage 1 with the only the smallest zone open. If your static pressure exceeds the max pressure for your air handler, you need a bypass.

    If your stage 2 comes on, it's because your thermostat / zone controller is calling for stage 2. You don't want stage 2 ON if any zone is closed. You didn't mention what type of zone controller & thermostat you are using?

  3. #3
    Join Date
    Jan 2004
    Posts
    60
    Quote Originally Posted by gonekuku View Post
    What's the max static pressure for your air handler? Hold the bypass closed - Run at stage 1 with the only the smallest zone open. If your static pressure exceeds the max pressure for your air handler, you need a bypass.
    Isn't that what variable drive does? Ramps up and down depending on static pressure?

  4. #4
    Join Date
    Jan 2004
    Posts
    60
    anybody?

  5. #5
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,686
    still digesting all the info you gave us to go on..........


    how about some model #s to work with.

    maybe even some pictures.....

    lennox does not want any bypass with their v drive blowers but we don't know what you have.

  6. #6
    Join Date
    Jan 2004
    Posts
    60
    zoning is ewc and York 9v furnace
    I don't mean any disrespect but is my question really brand dependent?

  7. #7
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,686
    not familiar with other brands but i know lennox does not want a bypass with v drive blower. i have read on here of other companies using bypass with v drive so i would say the answer you're looking for is brand dependent.

    hopefully some york guys will come along and let you know for sure.

  8. #8
    Join Date
    Apr 2004
    Posts
    7,680
    No you are right, the ECM is looking at the static. If it were me, I would open just the smallest zone and adjust the weight on the damper so it would not open as far. If the airflow through just that one zone is still too much, then I would incorporate minimum damper postions in the other zones to take some of the excess air.

  9. #9
    Join Date
    Nov 2007
    Location
    Chicago
    Posts
    76
    You do not install a barometric damper with a variable speed furnace. It will fool the fan. Variable speed works off of static pressure and as you noticed the barometric damper fools the fan and it doesn't know what to do. Any variable speed manufacturer's rep will tell you not to install a barometric damper. I would remove the bypass entirely. The static pressure sensor will back the fan down as the zones close.

  10. #10
    Join Date
    Aug 2006
    Location
    Chelmsford MA
    Posts
    1,518
    We use Arzel's modulating bypass damper with our zoned systems. They seem to work very well. I'm not a tech so I don't know the specs but our guys love the system.
    We only want to do it, if we can do it right.

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