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  1. #1

    2 stage chiller control

    I have a Johnson Controls as-unt1126-0 controlling a 15 ton trane office chiller with 2 circuits in it. Can someone explain under the bo points what the interstage delays do? I also have min on and min off times on the main window. I am guessing that interstage means time between stages coming on. but what does the off do. Does each stage need the interstage times set or just between the first stage and on the second stage set it to 0?
    On stage 1 the min on is set at 3:00 and the min off is set at 7:00 minutes
    On stage 1 interstage delay is set on 10:00 and off 0:00 minutes
    On stage 2 the min on is set at 2:00 and 5:00 off
    On stage 2 interstage delay is set on10:00 and off 0:00 minutes
    So does the interstage delay only need to be on BO-1 since there is not a 3rd stage?These are the numbers put in years ago when this was installed.

    Thanks for any info
    Wayne

  2. #2
    Join Date
    Oct 2008
    Location
    Atlanta, GA
    Posts
    187
    Quote Originally Posted by doubledose View Post
    I have a Johnson Controls as-unt1126-0 controlling a 15 ton trane office chiller with 2 circuits in it. Can someone explain under the bo points what the interstage delays do? I also have min on and min off times on the main window. I am guessing that interstage means time between stages coming on. but what does the off do. Does each stage need the interstage times set or just between the first stage and on the second stage set it to 0?
    On stage 1 the min on is set at 3:00 and the min off is set at 7:00 minutes
    On stage 1 interstage delay is set on 10:00 and off 0:00 minutes
    On stage 2 the min on is set at 2:00 and 5:00 off
    On stage 2 interstage delay is set on10:00 and off 0:00 minutes
    So does the interstage delay only need to be on BO-1 since there is not a 3rd stage?These are the numbers put in years ago when this was installed.

    Thanks for any info
    Wayne
    The interstage delays dictate how long the BO will go before activating or deactivating after sequencing. An example if you have an interstage on delay of 10 minutes and there is one chiller running and the controller calls for an additional chiller the controller will not energize the BO until the interstage delay has expired. The same goes for going down a sequence. There doesn't have to be a interstage up delay as you don't have the 3rd stage, but it will not give you just one stage delay that is why there are both on and off for the 2nd stage.

  3. #3
    Quote Originally Posted by NickDeal View Post
    The interstage delays dictate how long the BO will go before activating or deactivating after sequencing. An example if you have an interstage on delay of 10 minutes and there is one chiller running and the controller calls for an additional chiller the controller will not energize the BO until the interstage delay has expired. The same goes for going down a sequence. There doesn't have to be a interstage up delay as you don't have the 3rd stage, but it will not give you just one stage delay that is why there are both on and off for the 2nd stage.
    Sorry, I am still not clear. So does that mean if BO1 has interstage time on it that BO1 does not come on until that time period has expired or does BO1 come on when called for and it is the delay time until BO2 comes on for second stage.

    Wayne

  4. #4
    and it is the interstage delay time until BO2 comes on for second stage.

    Forgot to put the interstage in the last line

  5. #5
    Join Date
    Oct 2008
    Location
    Atlanta, GA
    Posts
    187
    Quote Originally Posted by doubledose View Post
    and it is the interstage delay time until BO2 comes on for second stage.

    Forgot to put the interstage in the last line
    The interstage delay on and off timers prevent the next stage from energizing or de-energizing until the interstage timer has expired. The interstage on timer for Stage 1 controls the elapsed time before Stage 2 may be turned on. The interstage timer for Stage 2 must elapse before Stage 3 may be turned on, and so on. The reverse is true for the interstage off timers. The interstage on of the last stage has no effect, and the interstage off of the first stage has no effect.

  6. #6
    BO will go before activating or deactivating after sequencing
    Thanks for clarifying ,what I did not understand was the above line.
    I am good now
    Thank you
    Wayne

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