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  1. #1
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95

    What temp is most critical at cold side?

    Well...

    Messing with a chiller, the mixture is Dowcal N 25%, approx freezing temp for the mix is -10degC/14degF. Measuring in the plate exchanger where the temp probe is placed i got -9degC/15,8degF, on outgoing water there's -6,5degC/20,3degF, can i turn down the thermostat (Carel PCO) or can the exchanger freeze over if i do so? The chiller is serving a bunch of disks at a grocery store, the manager want a li'l bit colder in a pair of disks, by this i have to lower the outgoing temp.

    By general. Which temperature is most critical? Exch. temp or outgoing temp?

    The chiller is running on 404A -18degC/-0,4degF evap, 40degC/104degF head. 8degC/14,4degF superheat, 5degC/9degF subcool.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,349
    the coldest temperature is the most important! whatever temperature you turn the thermostat to, please remember that the sensors do not know what the freeze point is, so the closer you run to the freeze point, the more you will want to check the fluids glycol concentration.
    "Mother" is the name for God on the lips and hearts of children....The Crow

  3. #3
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95
    Okay. As I suspected, thank you for the answer.

    Talked to my foreman 'bout this. He wanted me to move the probes to the in and outlet pipes instead of the exchanger position. But I didn't do this a thursday afternoon and overtime, you know Murphy and his laws? Also told him 'bout the issue with running too cold. He mentioned that the brine will thicken and loose circulation, but when that's happening the exchanger freeze is a fact. The outlet probes also works as freeze guards. Stupid...

    Anyhow... Will check the VKA:s coarse(? correct word?) and clean it if needed. May be clogged with old dirt and stuff...

  4. #4
    Join Date
    Sep 2002
    Posts
    2,728
    Best way to know freeze point in the cooler is suction pressure,many chillers used pressure as freeze protection,with time delay,worked great!You can get spot freezing!

  5. #5
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95
    Not this ol'bastard, just uses temp probes in the exchanger and mechanic pressure guards.

  6. #6
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95
    Oh this ol'bastard is equipped with regular pressure switches. One per circuit. There's 2 cicuits with 3 stages each. All compressors is the same size.

  7. #7
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95
    Well...

    Checked the dowcal mix with refractometer today. 38%, that'll give us a freezing point at -18degC/-0,4degF. Changed the probe calibration with 2degC/3,6degF so it's getting closer to in and outgoing pipe temp. Also lowered the inlet temp regulation with 1degC/1,8degF, when the chiller unloaded fully I had a outgoing pipe around -10degC/14degF, incoming was -4,5degC/23,9degF.

    Leaved the groce store satisfied. But amazingly surprised later same day, my foreman called, the disks was warm... Got there. Yup... Antifreeze alarm..., kicks in by -15degC/5degF. Reseted, fired it up, changed probe calib and inlet to more safe values. Let's se how this will appear

  8. #8
    Join Date
    Nov 2011
    Location
    North sweden, Umeň, Where the birches growing without limits.
    Posts
    95
    Oh well...

    Did almost forgot. Didn't find any coarses, think that's just straight pipes w/no filtration at all...

    DeltaT over the exch is 7degC/12,6degF when 5 stages of 6 is loaded. One stage is gone, shorted windings in that scroll.

    Worst of all... No papers for flow data in the exch etc...

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