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  1. #1
    Join Date
    Mar 2005
    Posts
    664

    compressor staging

    Hello gents, in the process of retrofitting some controls and wanted some ideas/opinions on compressor staging. what i have is a dx chiller with 4 circuits ,2 compressors each (30hp bitzer recip ) . Options 1)stage one circuit at a time fully loaded and carry on , or 2) load all circuits w/ 1 compressor before loading second? though latter will be better in amps and head pressure , I am leaning more towards the first, any thoughts? stan
    Keep it simple to keep it cool!

  2. #2
    Join Date
    Oct 2001
    Posts
    6,966
    what type of unit... process chiller or comfort cooling,and where is the TC-1 probe supply or return..Trane on the old style CGWC chillers with the W7900s ran up one circuit to full load then start a second after a certain time.don't want to start a second compressor if all it is going to do is knock back (unload)the lead compressor http://www.bestbuyheatingandaircondi...Code=MOD790A16
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  3. #3
    Join Date
    Mar 2005
    Posts
    664
    hi maxster , comfort cooling , will control on return water, the controls are going to multiplexer type compatible with the trend ems , not my choice, im just wiring and specifying programming strategy , I think I agree load one circuit full and carry on , still thinking about it though, and also wanna rotate compressor run times, stan
    Keep it simple to keep it cool!

  4. #4
    Join Date
    Oct 2001
    Posts
    6,966
    do you have air handlers with 3 way valves or a bypass so the chiller sees constant flow,load limiting if you can would be easier on the chiller instead as you noted getting full tonnage amps and head pressures just to make SP on a occup mode or restart. have you worked with the Honeywell W7900 chiller controller thing worked awesome and staged the semi-hermetics real easy as the loads changes.it staged up real slow no matter what the return water was and with you doing TC-1 control sensing there it gives you plenty of reaction time for loading and unloading...like return air controlling a rooftop.time delay staging in your EMS stuff might need some tweeking...check on those 3 ways and or a by pass on the loop...
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  5. #5
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
    1,330
    I think the W7909 is the way to go. In addition to staging up nicely, it has a load limit control that won't let a circuit fully load until the return water temp falls below a certain temp. This prevents the head pressure from getting high. When it is load limiting on return water temp, it will run both circuits unloaded.

  6. #6
    Join Date
    Mar 2005
    Posts
    664
    these are fcu with 3 way valves. unfortunately customer adamant using his bms controls , mainly for front end comms to office computer, I was pushing carel controls, declined. still wondering how I want to stage , kinda torn down the middle, and to rotate my compressors evenly to rotate between 4 circuits as next lead and fully load 1 at a time will be a hell of alot simpler to program then looking at 8 compressors. stan
    Keep it simple to keep it cool!

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