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  1. #1
    Join Date
    Jan 2013
    Posts
    10

    VFD for a 3 Ton residential air compressor

    Hi.

    I really get into idea of making my own custom made water cooled home AC system with capacity control based on how many rooms need cooling.
    I'm going to use zoning dampers to cut off the rooms & ECM motor to control the airflow.
    But on the ac side I'm not sure yet if I have to buy a copeland digital modulating scroll compressor(which seems to be very pricey for my own project) or put a VFD on a 3phase scroll compressor.

    The large enough VFD for 3 ton machine should be around 4HP? I found one on ebay relatively cheap for 135(item #290520222870) & compressor for 260(item #190755360553)
    My question is: VFD will be tough enough to carry LRA load of 88A on this compressor? & if yes, then how far with modulating of its speeds i can go up & down?

    thank you

  2. #2
    Join Date
    Apr 2007
    Location
    Amarillo by mornin'
    Posts
    855
    "It's not that I'm smart, it's that I stay with the problem longer”
    Albert Einstein

  3. #3
    Join Date
    May 2009
    Location
    in the present
    Posts
    92
    you will have oil return problems if you try to run a compressor at less than full speed.

  4. #4
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    Quote Originally Posted by kirkH View Post
    you will have oil return problems if you try to run a compressor at less than full speed.
    True, but I'm wondering if you could add an oil separator? Some mini split manufacturers go into oil recovery mode every hour where they ramp the compressor to 100% and open all expansion valves wide open.

    Are you wanting to use the vfd for a soft start or capacity control?

  5. #5
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
    Posts
    1,849
    I might be easier/cheaper to install an IAQ system.......
    Life is too short, Behappy!
    TFMM

  6. #6
    Join Date
    May 2008
    Location
    SouthEast
    Posts
    267
    i envy your enthusiasm, but i do not envy your journey...

  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    double..
    If more government is the answer, then it's a really stupid question.

  8. #8
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    I think that by the time you got it all sorted out, you may find that starting with an actual variable capacity system would have been a more economical choice.

    For my house, I'm going with a Daikin VRVIII-S system, with a conventional ducted air handler for the main living/kitchen area, ductless wall hangers for the bedrooms, and a ceiling mount for the garage.
    If more government is the answer, then it's a really stupid question.

  9. #9
    Join Date
    Dec 2008
    Location
    New York, ny
    Posts
    203
    Quote Originally Posted by mark beiser View Post
    I think that by the time you got it all sorted out, you may find that starting with an actual variable capacity system would have been a more economical choice.

    For my house, I'm going with a Daikin VRVIII-S system, with a conventional ducted air handler for the main living/kitchen area, ductless wall hangers for the bedrooms, and a ceiling mount for the garage.
    Nice system..

    Sent from my SGH-T999 using Tapatalk 2

  10. #10
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    Quote Originally Posted by grkmano View Post
    Nice system..

    Sent from my SGH-T999 using Tapatalk 2
    X2

  11. #11
    Join Date
    May 2008
    Location
    SouthEast
    Posts
    267
    Quote Originally Posted by mark beiser View Post
    I think that by the time you got it all sorted out, you may find that starting with an actual variable capacity system would have been a more economical choice.

    For my house, I'm going with a Daikin VRVIII-S system, with a conventional ducted air handler for the main living/kitchen area, ductless wall hangers for the bedrooms, and a ceiling mount for the garage.
    I've had my eye on those conventional ducted Daikin units for a while. Let me know how it performs. Also, what capacity did you select for it?

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