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Thread: Subcooling

  1. #1
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    Subcooling



    Hi guys
    Looking for some advice, After years of AC installations with iccassional fridge work I am now doing a lot more fridge work , predominantly cold stores, display cabinets , blast chillers etc,
    This has made me realise there are some things that I learnt back in college 16 years ago that has long been erased from my memory and I'm trying to make a massive effort to become an expert in these things

    I am starting with subcooling and wondered if you guys could recommend a good book, YouTube channel, or website that is English and uses celcious rather than Fahrenheit (it just confuses me sometimes they don't say which measurement they are using)

    And while I'm here maybe you guys could help me with afew questions
    1. If no details are on the name plate of the condensor is there a rule of thumb for the target subcooling in celcious? And does this Vary with different refrigerants and different types of equipment i.e. Air con, cold stores, chillers , freezers etc

    2. What would you guys aim to get the sub cooling to on a condensor for a fridge cold store with an exp valve and a 40 +metre pipe run? Would you stick to the rule of thumb or would you make adjustments to compensate the long run?

    3 when measuring with a temp probe for the subcooling so you place your probe immediately after the condensor?, at the liquid line service port, or somewhere else ?

    Really appreciate any responses
    Thanks in advance



  2. #2
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    Re: Subcooling

    Hi Lee,

    Subcooling, as important a factor as it is never seems to make the headlines is college teaching or various textbooks. Mention it to most fridge folk and you get a look like you're making to much of a fuss about nothing.

    1
    Anyhow, rule of thumb I'd say 5K subcooling measured at the receiver outlet is a good start and should follow for most types of system.
    I've checked systems short of charge and got subcooling of next to nothing, perhaps 1K.
    Checked Foster freezers (integrals) which looked short of charge (suction 5psi) but subcooling 8K, cap tube partially blocked. New cap tube and charged to plate gave figure around 5K I seem to recall.
    Shouldn't vary with refrigerant. Fridge systems seem similar. Never checked an AC but noted a VRV with a cool liquid line on full cooling (no faults, that's how it was). Subcooling must have been pretty high so AC might be a different kettle of fish. Not that it too much of an issue as the charge is worked out and inverters, EEV's and whatever mean the load is fluctuating anyhow so hard to make a lot of sense of it all.

    2
    5K at inlet to TEV ideally but you'd want a gauge port there as well. In practical terms full sight glass or subcooling by sight glass at 5K, whatever comes first, then see what your superheat is. Do this when room near setpoint.

    3
    Gauge line on receiver, probe at condenser or sight glass, doubt you'll see any difference. Infact at the other end of the liquid line hasn't been a lot different on systems I've checked it on.

    Gary on here did a good book called Tech Method. Think you have to by it from ebay now but those are the figures I remember and they've served me well.
    Last edited by Tayters; 23-06-2018 at 09:12 PM.
    Health and safety first..........unless I'm in a hurry.

  3. #3
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    Re: Subcooling

    Hi tayters

    Finally a reply I've been refreshing the page for over 24 hours and was starting to think my question didn't make sense.
    Thanks or the reply this will be really helpful, I do vaguely remember small bits of it at college but was always told by the engineers when I was an apprentice that superheat subccoling and enthalpy charts are a waste of time and you will never use them .
    Now I'm starting to realise how much time I would of saved if I'd learnt it when at college

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    Re: Subcooling

    You should know that subcooling and superheat has lot of uses in evaluation of system and therefore you need to know when to use some rule of thumb.
    From your question, it can be concluded that your interest in subcooling is related to evaluation of proper charge of refrigerant.
    Then you should also know that we charge systems and evaluate proper charge depending on type of metering device.

    Capillary=> superheat
    TXV=> subcooling
    EEV=> weight

    Reason for that is in how each of metering device function in system.
    Therefore, I suggest that you thoroughly study each system function and used elements before using any general rule of thumb in order to be excellent in your job.

    I recommend Gary's Refrigeration 101 thread here as start, and use search function of this forum for recommended books, as they are recommended many times here.

    http://www.refrigeration-engineer.co...geration-Books

    http://www.refrigeration-engineer.co...shooting-Books
    Last edited by nike123; 16-07-2018 at 10:42 PM.
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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