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  1. #1
    Join Date
    Apr 2010
    Location
    Ontario
    Posts
    474

    Coolling tower converted to vfd

    Some company converted the closed loop cooling tower to vfd.
    Vfd controlled by loop temperature.
    Used to be a two speed motor.
    They ignored the tower dampers and spray pump .
    Now I have the tower dampers, spray pump and a vfd that don't work together.
    Anyone know if BAC or Marley has docummentation on how to make this work properly.
    ENJOY THE RIDE

  2. #2
    Join Date
    Feb 2013
    Location
    Phoenix, AZ
    Posts
    198
    I've done several closed loop towers (sometimes called fluid coolers here), never seen one with dampers.

    I always do the same sequence. On rise in temp above SP, spray pump on. Further rise, fan on, min speed, then modulate speed up. On fall in temp, modulate speed down to min. On fall below SP (approx. 2 deg.), fan off. On further fall, spray pump off.

    How are the dampers arranged? Do they have actuators? What controls them now? Something new to me...

    Sent from my ADR6300 using Tapatalk 2

  3. #3
    Join Date
    Mar 2007
    Posts
    3,124
    I would use the same control sequence described above and lock the discharge dampers open or cut them out altogether.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  4. #4
    Join Date
    Feb 2013
    Location
    Phoenix, AZ
    Posts
    198
    Are the dampers a cold weather thing? We dont see them here in sunny Phoenix.

    Sent from my ADR6300 using Tapatalk 2

  5. #5
    Join Date
    Mar 2007
    Posts
    3,124
    Modulating discharge dampers are used on forward curved fans as a means of condensing temperature control in cold weather.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  6. #6
    Join Date
    Feb 2013
    Location
    Phoenix, AZ
    Posts
    198
    Quote Originally Posted by Tech Rob View Post
    Modulating discharge dampers are used on forward curved fans as a means of condensing temperature control in cold weather.
    Got it. Then yes, it would make sense to just lock open or remove with a VFD retrofit.

    Sent from my ADR6300 using Tapatalk 2

  7. #7
    Join Date
    Mar 2010
    Location
    Kent, WA.
    Posts
    189
    The dampers might not be modulating. Ive worked on several towers where the dampers are used to retain the heat in the tower in the winter to aid the sump heaters. If these are this type of damper i would use the call for spray pump to open them and the end switch to enable vfd. Then use loop temp to start and control vfd with a 4-20 signal.
    Experience
    Is what you get when you didn't get what you wanted.

    A positive attidude will not solve all your problems, but it will annoy enough people to make it worthwhile.

  8. #8
    Join Date
    Mar 2008
    Location
    NC
    Posts
    1,461
    The dampers might not be modulating. Ive worked on several towers where the dampers are used to retain the heat in the tower in the winter to aid the sump heaters.

    x2

  9. #9
    Join Date
    Mar 2007
    Posts
    3,124
    I guess that could also be what they're for. Especially up there in Ontario. I have never seen a setup like that.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  10. #10
    Join Date
    Mar 2010
    Location
    Kent, WA.
    Posts
    189
    I also forgot to mention not just aiding the sump heaters but keeping the heat exchanger from freezing in a closed loop tower. Ive seen this setup more on evapco's than anything. of course the damper motor will fail in the middle of summer and will stump you if you have not seen this before.
    Experience
    Is what you get when you didn't get what you wanted.

    A positive attidude will not solve all your problems, but it will annoy enough people to make it worthwhile.

  11. #11
    Join Date
    Jun 2002
    Location
    south jersey
    Posts
    1,116
    The dampers always tend to lock up and rust open or closed.
    You need to put the phone down and get back to work!

  12. #12
    Join Date
    Apr 2010
    Location
    Ontario
    Posts
    474
    Got back to the site.
    The new vfd is set to maintain 80*f. The sensor is down in the mechanical room.
    On the roof the rest of the control system remains. The sensor is at the cooling tower.
    Modulating discharge dampers at the fans were still in operation. I disconnected them and left fully open. These were to control capacity, but now the vfd does it.
    In the next few weeks I'll be putting water back into the tower sump and the spray pump will come into play.
    Nice if they'd use one temperature sensor to control everything.
    ENJOY THE RIDE

  13. #13
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    372
    I would use the dampers as stage one then as DDC dan says stage on the rest.You would think the dampers would be up on the outlet of the tower to keep as much heat in the bundle.What protects it from the cold weather now? With no sump water and sump heat there must be a 3way valve thats left cracked opened or is the bundle drained also?

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