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  1. #1
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    Strange cooler operation (high superheat)



    Hi Everybody, hope you all are fine !

    Please, I am posting here a case that is puzzling me

    here is the case

    I have an evaporator in a cold room with following set points

    - air inlet temperature 0.32F
    - evaporating temperature -27.4 F

    Now starts the strange things.

    I am measuring a superheating of 15K.
    Yes, 15K !!

    I made some verifications
    - theoretical, with evaporator manufacturer, to see capacity in working conditions
    - measuring air inlet/outlet temperatures. with manufacturer air flow I calculate a capacity similar to the one


    all let convey that I can open the valve, so that I can get more refrigerant and therefore more capacity

    But when I do this, I have fluid in compressor. All the compressor start to frost. Not only the beginning, the whole compressor.
    The evaporator starts to frost in all rows

    My interpretation is that there is a problem with the valve.

    Please, could anybody give me an opinion about ?

    as a general question.
    What would happen if an expansion valve is not working properly ?


    Many thanks !



  2. #2
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
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    Re: Strange cooler operation (high superheat)

    Is the room down to temperature? If not then wait until it is and then take another set of readings.

    15K superheat, OK, has it changed from when you last checked the system?
    Brian - Newton Abbot, Devon, UK
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    Re: Strange cooler operation (high superheat)

    .

    What is the refrigerant?

    Where are you measuring the suction pipe temperature?

    To get true evaporator superheat you need to measure both
    the pressure and temperature as near to the outlet of the evap
    as possible.

    If you are measuring the pressure at the compressor there will always
    be a slight difference. Also the refrigerant is important, is it a blend
    or a single refrigerant? Is it a 400 series refrigerant or are you using R22?

    Blended refrigerants (400 series) have a glide in the evaporating temperature,
    it is very important that you know which side of the glide you are measuring.

    If you are working with a blended refrigerant (400 series, zeotropic) you always
    measure evaporator superheat from the Dew point temperature or sometimes it
    is refereed to as the Vapour temperature.

    Rob

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    Re: Strange cooler operation (high superheat)

    Hello, sorry for not being precise
    - refrigerant is R507A, therefore no glide topics
    - the most important element is that all the compressor starts to frozen when I open the valve, so that I get liquid going to the compressor, with the risk of damaging it.

  5. #5
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    Re: Strange cooler operation (high superheat)

    Then don't open the valve.
    Brian - Newton Abbot, Devon, UK
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    Re: Strange cooler operation (high superheat)

    Quote Originally Posted by Brian_UK View Post
    Then don't open the valve.


    Rob

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  7. #7
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    Re: Strange cooler operation (high superheat)

    Hi Paul
    Couple of checks to make:
    Is the evaporator coil clear and air flow is correct?
    Measure pressure and temp at evaporator as Rob says?
    Check there is sufficient refrigerant in system.
    Record suc & discharge pressures at compressor
    I love the smell of Ammonia in the morning!

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    Re: Strange cooler operation (high superheat)

    It's really strange the fact that with 15K superheat you get the vapour refrigerant temperature (evaporator outlet) at the same temperature the air inlet...meaning on theory you have a lot of lack of refrigerant flowing inside the evaporator. Where are you measuring the suction superheat? If you measure after a liquid subcooling heat exchanger with the vapour passing through it or if you measure the SH near the compressor of course an higher SH will happen.
    To make progress is never good enough, I want to do better and better and better

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    Re: Strange cooler operation (high superheat)

    Quote Originally Posted by Sandro Baptista View Post
    It's really strange the fact that with 15K superheat you get the vapour refrigerant temperature (evaporator outlet) at the same temperature the air inlet...meaning on theory you have a lot of lack of refrigerant flowing inside the evaporator. Where are you measuring the suction superheat? If you measure after a liquid subcooling heat exchanger with the vapour passing through it or if you measure the SH near the compressor of course an higher SH will happen.
    If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.

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    Re: Strange cooler operation (high superheat)

    Quote Originally Posted by palmerm View Post
    If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.
    Its always a possibility worth checking, but you would think it would flood all the time.
    We are not hearing the basics of refrigerant charge, subcooling, piping detail, bulb position, way in which superheat is measured, air flow etc etc, so it's all guess work.

  11. #11
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    Re: Strange cooler operation (high superheat)

    Quote Originally Posted by palmerm View Post
    If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.
    Palmerm, Ranger is right...it would flood all the time no matter what adjust you made to the expansion valve...
    To make progress is never good enough, I want to do better and better and better

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