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  1. #1
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    Calculating Tonnage of refrigeration machine


    Hello all, i'm an engineering intern trying to calculate the tonnage of an electric brine refrigeration machine. I read the info on the motor and it's a: 223 amp motor, 2300 volts, 900 HP. Anyone know how to calculate tonnage?



  2. #2
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    Re: Calculating Tonnage of refrigeration machine

    That will not work. You need to find the operating conditions of the refrigeration system and a copy f the compressor manufacturers performance data.

    Anything else is just a wild guess.
    If all else fails, ask for help.


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    Re: Calculating Tonnage of refrigeration machine

    I have a list of real-time operating conditions:

    Comp TEJ Bearing Temp Comp SEJ Bearing Temp Comp Thrust Bearing Temp Comp Oil Reservoir Press Comp Oil Temp Comp BRG Oil Supply Comp Back of Seal Oil Press Comp Oil Diff. Press Comp Discharge Gas Temp Comp Bearing Oil Supply Temp Gear/Motor Oil Supply Temp Motor Amps Cond. Enter Water Temp Cond. Exit Water Temp Cond Refrigerant Temp Cond Refrig. Press Evap Refrig. Press Brine Entering Temp Brine Leaving Temp Main Brine Loop Temp Evap Refrig. Temp Economizer Refrig. Temp Control Air Press Local Temp Set Pt. PID Out
    I'm wondering if I can use the motor amps and voltage to get HP and use that to calculate tonnage..

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    Re: Calculating Tonnage of refrigeration machine

    Sorry, here it is in list form:

    Comp TEJ Bearing Temp
    Comp SEJ Bearing Temp
    Comp Thrust Bearing Temp
    Comp Oil Reservoir Pressure
    Comp Oil Temp
    Comp BRG Oil Supply
    Comp Back of Seal Oil Press
    Comp Oil Diff. Press
    Comp Discharge Gas Temp
    Comp Bearing Oil Supply Temp
    Gear/Motor Oil Supply Temp
    Motor Amps
    Cond. Enter Water Temp
    Cond. Exit Water Temp
    Cond Refrigerant Temp
    Cond Refrig. Press
    Evap Refrig. Press
    Brine Entering Temp
    Brine Leaving Temp
    Main Brine Loop Temp
    Evap Refrig. Temp
    Economizer Refrig. Temp
    Control Air Press
    Local Temp Set Pt.
    PID Out

    I'm wondering if I can use the motor amps and voltage to get HP and use that to calculate tonnage..

  5. #5
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    Re: Calculating Tonnage of refrigeration machine

    all you need are these:
    Cond Refrig. Press
    Evap Refrig. Press

    Convert the pressures to the saturation temperatures for the specific refrigerant used in the compressor. Now look these temperatures up on the compressor manufacturers performance charts. They list the compressor performance based on saturated inlet (suction) and condensing temperatures.
    If all else fails, ask for help.


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    Thumbs up Re: Calculating Tonnage of refrigeration machine

    Quote Originally Posted by US Iceman View Post
    all you need are these:
    Cond Refrig. Press
    Evap Refrig. Press

    Convert the pressures to the saturation temperatures for the specific refrigerant used in the compressor. Now look these temperatures up on the compressor manufacturers performance charts. They list the compressor performance based on saturated inlet (suction) and condensing temperatures.
    Great! Thanks so much for the help

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    Re: Calculating Tonnage of refrigeration machine

    Here is what I do. First you need to have the manufactures performance data at 25 different Suction and discharge temperatures. These are laid out in a matrix. 5 suction by 5 discharge. These will be shown as Tons of refrigeration and Brake Horse Power. By running these numbers through a nasty equation you can come out with that compressors performance at any given suction and discharge temperature. If the compressor has a VFD just use the speed as a direct multiplier. If the compressor is a screw and is running at a part load it is not a linear conversion. You would need to find out how the slide valve affects capacity at different positions. So 90% slide valve does not mean 90% capacity. There is a nasty equation for that too. Recips are linear.

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