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  1. #1
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    Sub cooling and superheat



    No it`s not another "how do measure sub cooling etc" question. Well not exactly. I`m just asking as I`m pondering how s/heat and s/cooling are measured when there`s as fan pressure switch that obviously causes the HP and LP ( to some extent) to rise and fall. Do I need to restrict the airflow over the condensor to keep the fan running, and hence the pressres steady, or do I take the midway point on the HP and LP gauges, and on the temperature readings.

    Thanks in advance for any ideas,
    Glenn



  2. #2
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    Re: Sub cooling and superheat

    .

    No the superheat or subcooling value should remain constant.

    If the discharge pressure rises the condensing temp rises but subcooling should still
    be the same value.

    The same with evap superheat.

    So if the evap is evaporating at 0 deg C and the suction pipe temp is +6 deg C then
    the superheat is 6 deg's differance. If the evap temp drops to -5 deg C the suction
    pipe temp should drop also (to about +1 deg C) and the supeheat will still be 6 deg's.


    Cheers

    taz

    .

  3. #3
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    Re: Sub cooling and superheat

    Hi Taz and thanks for the quick reply
    I see what you mean about the pressure /temperature.The problem I have is on a hiross chiller, the fan on pressure is 20 bar and off at 15 bar (r407c). The pressure rise is quite rapid, about twenty seconds and the drop time about ten seconds. In that time there`s very little time to note any temperature rise. Maybe I need to win the Lottery and splash out on a Testo manifold so I can get real time measurements.
    Thanks again Taz

  4. #4
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    Re: Sub cooling and superheat

    .

    Hi Glenn.

    If your head pressure rises to 20 bar over twenty seconds or so and then drops to 15 bar
    over ten seconds, are you saying the fan is constantly cycling on and off at about thirty
    second intervals?

    A five bar rise and fall over the time span is a bit quick and might not be good??

    Cheers

    taz

    .

  5. #5
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    Re: Sub cooling and superheat

    To measure SH and SC you do need some level of stability, which you do not have.
    Does it work OK, then there is agood chance it is OK.
    When cycling best test SH at compresor inlet, ensure it never gets to low

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