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Thread: Differential Setting for dual chillers?

  1. #1
    Join Date
    Jun 2011
    Posts
    203

    Differential Setting for dual chillers?

    We have a 20hp glycol chiller that is 2 10hp units working in tandem (when necessary).

    We have been running the sytem with both units set to chill to 25*. One unit will be set to turn on if glycol temp reaches 26 and the other is set to kick in when it reaches 27.

    Do you think I should make the differential between the 2 larger than a single degree? Am I at risk of short cycles on the unit currently set as the secondary?

    The system has been working fine as is, but it was time for me to switch which is the primary and secondary units to balance wear and it got me to thinking about this...

    Thanks,

    Brian

  2. #2
    Join Date
    Jan 2003
    Location
    Palau
    Posts
    1,938

    Our SOP is to switch the units monthly...

    I use the differential that you use, but also switch the primary from #1 to #2 every month to wear the units similarly. #1 unit runs as primary during odd months, #2 for even. Only way to know short-cycling is to run the system and listen to it.
    Phillip Kelm--Palau Brewing Company Manager--

  3. #3
    Join Date
    Jun 2011
    Posts
    203
    Quote Originally Posted by gitchegumee View Post
    I use the differential that you use, but also switch the primary from #1 to #2 every month to wear the units similarly. #1 unit runs as primary during odd months, #2 for even. Only way to know short-cycling is to run the system and listen to it.
    Ive been switching every 6 months - maybe I should do it a little more often. Next warm weather day we get I'm setting up a beach chair next to the chiller and working on my tan to "check for short cycles".

  4. #4
    Join Date
    May 2012
    Location
    Livermore, CA
    Posts
    596
    You can add a delay on break anti short cycle switch for each controller. They are adjustable and you can set how long in minutes the compressor would be locked out. That is pretty standard for some of the higher end units that can see varying loads.

  5. #5
    Join Date
    Jan 2003
    Location
    Palau
    Posts
    1,938

    What he said....

    Forgot about time delay relays. Use them not only to stop short cycling, but also to keep high powered refrigeration equipment from starting with brown power when your electrical service is restored after a blackout interruption. Better to wait a few minutes for power to establish before starting refrigeration equipment.
    Phillip Kelm--Palau Brewing Company Manager--

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