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  1. #1
    Join Date
    May 2007
    Posts
    156

    Centrifugal Chiller Cycling

    We have 3 Trane Chillers 350Ton each,2 Operational 1 Standby.Supply Temp 44F and Ret 49-52.If we want to Cycle Chillers Off/On which temp is preferred to follow Supply or Return.Thanks.

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,278
    Quote Originally Posted by coldrig View Post
    We have 3 Trane Chillers 350Ton each,2 Operational 1 Standby.Supply Temp 44F and Ret 49-52.If we want to Cycle Chillers Off/On which temp is preferred to follow Supply or Return.Thanks.
    Supply temp, but why not cycle/RESET based upon actual demand?

    There are times when one can getaway with this, I recommend contacting your controls company for some more insight into this

  3. #3
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,609
    With water flow balanced to design, cycle your lag based on return temp. That way you only run the lag if the load calls for it. If you have a less than desirable system design or changes have been made and you need more flow than cooling, then you need to base it on chiller loading or plant loading.

  4. #4
    Join Date
    Dec 2009
    Location
    northeast pa
    Posts
    118
    why not ran chiler based on outside temp there is % verse outside temp

  5. #5
    Join Date
    Sep 2007
    Location
    Somewhere in the world.
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    1,577
    If it is controled by automation demand would be another option if you have 2 chillers running at a reduction in load thats not very efficient plus you could implement a rotation schedule to exercise all the chillers for equal run time at least the idle chiller will have its share because when the need is there at least you know it works to.
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  6. #6
    Join Date
    Jul 2001
    Location
    maryland
    Posts
    1,353
    There are many different options for controlling lead/lag in a chiller plant, so you can expect to get many different opinions on how it should be done.

    If all three chillers are 10 degree chillers then you have a 10 degree plant so I would stage them the way the Trane Chiller Plant Control application would control them if you're using the temperature scheme.

    The first chiller is enabled as long as the plant is enabled. The second chiller is enabled if the water differential temperature exceeds design temp (10 degrees) for a certain amount of time. Same thing for the third chiller.

    The lag chillers are staged off by using design temp as well. If you have two chillers online then the lag chiller will be staged off when the differential temp is less than 5 degrees for a certain amount of time. If three chillers are online then the lag chiller is staged off when the differential is less than 3.3 degrees.

    Easy and it works well until you can more than 4 or 5 chillers, then you stage them on/off with flow demand.
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  7. #7
    Join Date
    Jan 2011
    Location
    Nashville,Tn
    Posts
    80
    We have 3, 1250 ton Tranes ( with plate and frame for winter ) and use outside temp as the control.
    First chiller on line above 38 degree, second on line at 70, third at 90 to 93.
    ( below 38, plate and frame takes the load )
    Maintain 43 (f) supply to hospital at all times.

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