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  1. #1
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    Question (stupid?) Should system be at saturation pressure?



    Hello,

    I am a newbie but have not really been able to find a definitive answer to this basic question.

    Should all refrigeration systems be at saturation pressure when at rest?
    In other words, should the gauges indicate ambient temperature?

    Best regards
    B



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    Re: Question (stupid?) Should system be at saturation pressure?

    If off for 1 hour or so, I would say yes.

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    Re: Question (stupid?) Should system be at saturation pressure?

    You need to look at a temperature/pressure chart for the particular refrigerant type you are using.

    Pressure varies with temperature so your gauge reading will vary with ambient temperature changes, when the system is at rest.

    https://nationalref.com/technical/pt-chart/

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by frank View Post
    You need to look at a temperature/pressure chart for the particular refrigerant type you are using.

    Pressure varies with temperature so your gauge reading will vary with ambient temperature changes, when the system is at rest.

    https://nationalref.com/technical/pt-chart/
    So back to my question, should ANY refrigeration system at rest, equalised and left for a day be showing the ambient temperature on the appropriate gauge for that gas?

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    Re: Question (stupid?) Should system be at saturation pressure?

    Question is to open when you say ANY system, as say if a freezer suction pressure could be freezer saturated temperature , if insulated vessel with level of chilled refrigerant from when it was running the day before, the list could go on.
    Is there a reason you ask?
    Turn it off for longer, say more than a week for large system, all rooms& doors open.
    Sun, shade, day, night, freezer floor could have minor influences.
    A lag time could also happen for things to warm up, cool down.
    Last edited by RANGER1; 19-12-2023 at 09:57 AM.

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by RANGER1 View Post
    Question is to open when you say ANY system, as say if a freezer suction pressure could be freezer saturated temperature , if insulated vessel with level of chilled refrigerant from when it was running the day before, the list could go on.
    Is there a reason you ask?
    Turn it off for longer, say more than a week for large system, all rooms& doors open.
    Sun, shade, day, night, freezer floor could have minor influences.
    A lag time could also happen for things to warm up, cool down.


    Okok, I will re-phrase it again:

    Are all refrigeration systems supposed to be charged with enough gas to be at saturation when at rest and the gas is at ambient temperature?

    I ask because I think it is a very important principle that I am not sure of and it has not been explained anywhere I can find.

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    Re: Question (stupid?) Should system be at saturation pressure?

    ................
    Last edited by seanf; 20-12-2023 at 10:17 AM.
    Interested to hear about opportunities to learn - linkedin.com/in/s34nf

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by berntd View Post
    Okok, I will re-phrase it again:

    Are all refrigeration systems supposed to be charged with enough gas to be at saturation when at rest and the gas is at ambient temperature?

    I ask because I think it is a very important principle that I am not sure of and it has not been explained anywhere I can find.
    The problem is for me there is no example of your “problem “ or system you are referring too.
    There are system with different designs.
    For example a scientific ultra low temperature cascade system has a vessel on suction side to allow for expansion of gas only in the system when off.
    Probably critical charged, no liquid receiver.
    I’m no expert on them, but what I am saying is there are specialised systems out there.
    Pick a simple system, rephrase again.
    What systems do you work on?

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by RANGER1 View Post
    The problem is for me there is no example of your “problem “ or system you are referring too.
    There are system with different designs.
    For example a scientific ultra low temperature cascade system has a vessel on suction side to allow for expansion of gas only in the system when off.
    Probably critical charged, no liquid receiver.
    I’m no expert on them, but what I am saying is there are specialised systems out there.
    Pick a simple system, rephrase again.
    What systems do you work on?
    I see what you mean.

    I personally work with small simple refrigeration systems.
    Compressor, evaporator, condenser dryer and capillary tube. Not even expansion valves.

    But my questions was meant for the wider range of general systems as usually described in text books.

    Best regards
    B

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by berntd View Post
    I see what you mean.

    I personally work with small simple refrigeration systems.
    Compressor, evaporator, condenser dryer and capillary tube. Not even expansion valves.

    But my questions was meant for the wider range of general systems as usually described in text books.

    Best regards
    B
    No worries,
    Show pictures or diagram that you have questions on.
    Then you can get various opinions etc

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    Re: Question (stupid?) Should system be at saturation pressure?

    Hi
    System fild with pure refrigeration and without any other gas (Air or other Gas ) gage is showing the ambient temperature.
    But pure Gas in the market is %99
    And System has other Gas in the inside of pipe.
    Also measuring of Gage has a tolerance on the reading and measuring.

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    Re: Question (stupid?) Should system be at saturation pressure?

    Quote Originally Posted by mbc View Post
    Hi
    System fild with pure refrigeration and without any other gas (Air or other Gas ) gage is showing the ambient temperature.
    But pure Gas in the market is %99
    And System has other Gas in the inside of pipe.
    Also measuring of Gage has a tolerance on the reading and measuring.

    Thank you for confirming that.

    Best regards
    B

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    Re: Question (stupid?) Should system be at saturation pressure?

    If I may offer my thoughts,
    A static system(non operational) is to be observed it should in principal should act as a singular vessel if there is a proven path for equalisation through either the compressor, expansion device or both. Depending on these paths and the systems volume of refrigerant will determine the rate at which any liquid may migrate/evaporate.

    I assume since you said PURE refrigerant you already have an understanding of the gas laws and and ruling out Dalton's law of partial pressures ?

    With that i mind you can see that depending on the system design you can see that, when not operating, a system can only show you the refrigerant vs ambient temp (across all points of the system).

    So if you prefer you can see it this way ....if you have a bottle of refrigerant completely full of liquid what happens when the ambient changes?
    If the bottle is totally vapor can you form liquid by altering the ambient temperature?

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    Re: Question (stupid?) Should system be at saturation pressure?

    I have to continue this thread as I am still confused....

    So I asked and was answered here that the gas pressure in a refrigeration system at rest should be saturated and thus show approximately the ambient temperature on the gauge.

    We have a smallish R290 system in the lab that shows -2dC (R290 gauge) pressure (at rest) where the ambient temp is actually +20dC, indicating that the system is way below saturation pressure.

    I questioned this and mentioned that there is too little gas in the system but got told I have no idea what I am talking about.

    So now I am back here wondering again.

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    Re: Question (stupid?) Should system be at saturation pressure?

    You are probably right-but remember that the pressure will relate to the coldest part of the system in a single compressor evaporator. unit.

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    Re: Question (stupid?) Should system be at saturation pressure?

    The system is no bigger than a 15x20x15" and has been sitting on a lab table for days, not being operated.

    I can't elaborate here in public :-(

    I can discuss in private.

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    Re: Question (stupid?) Should system be at saturation pressure?

    You may be right, but
    Does it reach correct temperature when running.
    Can you read pressures & temperatures when running, suction & discharge pressure, box temperature etc.
    That would most likely prove what you suspect.

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    Re: Question (stupid?) Should system be at saturation pressure?

    Hi Guys,magic 8 ball online
    No question is stupid! To address your question, whether a system should be at saturation pressure depends on the specific application and requirements. Saturation pressure is often desired in certain processes such as refrigeration or power generation, but it's not a universal requirement for all systems.

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