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  1. #1
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    Low Temp, Compression Ratio


    Hello,
    can i know what is the max compression Ratio for semi-hermetic comp 1 stage. for low temp (et -30C)
    r22 LP 2psi, HP 245psi.

    regards.
    w.l.ong



  2. #2
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    Re: Low Temp, Compression Ratio

    It all depends on compressor type and brand. For sure you will not be able to buy a compressor with a 245/2=120 times compression ratio. More likely ratio=from 6 to 10.

  3. #3
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    Re: Low Temp, Compression Ratio

    You will need to bring your head pressure down ,somehow,or that compressor will burn up.With that compression ratio like that, even a two stage would be in danger of burning up.

  4. #4
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    Re: Low Temp, Compression Ratio

    2 psig (16.8 psia) = approximately -36F
    245 psig (260.8) = approximately 116F

    Pressure ratio = 260.8 / 16.8 = 15.6:1

    That's too high for a single stage recip to be reasonable. A screw compressor may be an acceptable choice for single stage duty, BUT, this is a rather severe duty to expect a long life from the compressor.

    For an industrial duty screw compressor this is possible. For a commercial duty screw compressor it might work OK for a reasonable time.

    For a recip. compressor operating with one stage, the max. compression ratio (Pressure ratio) would be as NoNickName mentioned. 6-10 would be the maximum.
    If all else fails, ask for help.


  5. #5
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    Thumbs up Re: Low Temp, Compression Ratio

    Hi there,

    Try to use Demand Cooling compressor. The manufacherer data states that you can do that.
    BUT remember this type of compressor is good for cold product, i.e. the product comes into the cold room cold. Like ice cream or frozen products. If it is subjected to hot or warm product all the time, there will be problems for compressor.
    Cheers
    Even Einstein Asked Questions

  6. #6
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    Re: Low Temp, Compression Ratio

    last weeks, i change the txv, the txv valve is jamm...

    now the suction pressure is high...
    LP: 14psi HP:275psi...
    the room temp rich -25C..all ok..

    Thank for help...

    w.l.ong

  7. #7
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    Re: Low Temp, Compression Ratio

    Quote Originally Posted by w.l.ong View Post
    last weeks, i change the txv, the txv valve is jamm...

    now the suction pressure is high...
    LP: 14psi HP:275psi...
    the room temp rich -25C..all ok..

    Thank for help...

    w.l.ong
    Hi Ong,
    Glad to hear that you solved the problem.

    I have to say that if you are using a single stage compressor with R22, make sure that the operating conditions are within the recommended envelop of the manufacturer. If the compressor is not recommended to use in those conditions then you will have a compressor break down in the future.
    The reason is simple: if the minimum operating evaporating temperature of the compressor is -25C and it is operated at -30C then the compression ratio would be high which would lead to high discharge temp. and then compressor would get warmer and hotter in time which would make its life shorter.
    Hope this helps.
    Lana
    Even Einstein Asked Questions

  8. #8
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    Re: Low Temp, Compression Ratio

    Helo Lana,

    i am using low temp compressor it from germany..
    the operating limit is -20C to -45C for R22.
    the comp. oil sum body temp is abit hot, i can't hold it more then 5 sec... suction pipe is iceing.

    i can said that this comp. ratio is about:
    LP: 14 psi HP: 275 psi ratio about 10.1 : 1
    am i right?

    regards.
    w.l.ong

  9. #9
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    Re: Low Temp, Compression Ratio

    Hi Ong,

    The compression ratio must be calculated with absolute pressures NOT gauge pressure.
    The compressor is correct for your application. Make sure that additional cooling is not required for the compressor. I mean cooling with additional fan or water circuit.
    Also, these kinds of compressors are good for cold products only, as I said before.
    Hope this helps.
    Cheers
    Even Einstein Asked Questions

  10. #10
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    Re: Low Temp, Compression Ratio

    Hello Lana,
    yes i already add the absolute pressures + pressure gauge
    to get the pressure ratio...

    w.l.ong

  11. #11
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    Re: Low Temp, Compression Ratio

    We have some Copelands running on R22 with the given pecs (freezer application)
    It are Demand Cooling compressors (liquid injection in a special channel inside the compressor)
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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