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Thread: cactus56

  1. #1
    Join Date
    Dec 2011
    Location
    Tampa fl
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    16

    cactus56

    Hello
    I have a customer with a carrier split unit(38auzb12a) set up for 100% fresh air ,installed by another contractor,no capacity control,running copeland scroll
    (zp102k) compressor, starting and stopping comp on supply air temp. room temp fluctuating with compressor cycles. what do you think about running the comp with an inverter controlled by supply air temp? copeland is now offering a 5ton and down inverter controlled comp, unloading down to 40%.
    This unit is just over 1 year old ,dont want to install hot gas bypass if inverter will work.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,168
    You would also need a VS blower.

    Hot gas would probably be better. Check out a Rawal valve.
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  3. #3
    Join Date
    Dec 2011
    Location
    Tampa fl
    Posts
    16
    Thanks beenthere, application in hospital isolation rooms (2 rooms). airflow balanced to negative pressure relative to common hallway outside iso rooms, cannot vary supply air. I have used rawal device on other jobs, customer has spent so much on this system already with previous contractor,trying to help keep cost down. hospital has inverter easy and quick install without taking refrigeration down to install hot gas bypass. My question, has anyone used inverter on larger scroll compressors? guestimate on minimum speed to maintain oil flow? trying to think outside box.
    Thanks
    choya56

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,168
    I haven't. but i believe you'll find you would need a compressor made to use an inverter. Which means it would be better to buy the compressor then try to retro fit an inverter to the one you have.
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  5. #5
    Join Date
    Dec 2011
    Location
    Tampa fl
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    Thanks
    Choya56

  6. #6
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    100% OA needs discharge air temp control with a heating cooling and neutral setpoint based on t-stat calls. Then it also needs to dehum to maintain max leaving air dewpoint or at least max space RH. This typically requires a hot gas reheat coil. 100% OA is typically not comfortable without modulating microprocessor controls on everything. Blower should be constant volume for healthcare code vent reqs

  7. #7
    Join Date
    Dec 2011
    Location
    Tampa fl
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    Thanks
    19characterusername

  8. #8
    Join Date
    Dec 2011
    Location
    Tampa fl
    Posts
    16
    Hello Folks
    We did it , used honeywell spyder to monitor conditions and control inverter, rooms now usable. Hasn't gotten really hot or humid yet but all conditions meeting spec now, may have to tweak later. Running about 40% minimum speed ref. All ok, will post more info later date

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