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  1. #1
    Join Date
    Aug 2002
    Location
    Sacramento area
    Posts
    70
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    Confused Liebert XDC Chiller Pump "Loss of Flow" Issues

    How many people are having flow loss issues with the Liebert XDC Chillers that use R-407C to cool the pumped R-134a? Also, is there anyone who has NEVER had this occur?

    We've determined multiple times that when an additional compressor stages on, the chilled R-134a pressure drops so fast that it loses subcooling at the pump inlet and flashes, even with a vessel half filled with liquid a few feet above the pumps. This loss of subcooling (flashing) causes the differential pressure switch to sense loss of flow. When this occurs and nobody is around, the server room temp gets out of control. When a technician is there, the SMA-12 test instrument is used to take control of the hot gas valves (Sporlan SDR valves) to prevent abrupt changes in pressure after an additional compressor stages on. It is a slow tedious process to keep the chiller running, by only moving the SDR valve for 1 to 4 seconds at a time, about once every minute or so. If the change happens too quickly, you lose flow and the compressors shut off, then you start all over again.

    The plate & frame heat exchanger is so efficient that it makes the R-134a flow become very sensitive to changes in the R-407c temperature changes.

    Does anyone have any suggestions as to the root cause of the problem?

    Has anyone come up with a solution to this problem?

    We have the XDC 160 (46 ton) chiller with 7 overhead XDO cooling coils. We have 2 bypass flow regulators (Griswold valves) and have tried all of the different combinations of closing the ball valves at one or both or neither bypass regulators. We don't have a pump curve or any information to verify the actual gpm of flow, but we're told that our flow is good because we have about 35 psig increase through the pump.
    I'm still learning this trade.

  2. #2
    Join Date
    Apr 2006
    Location
    mechanical room
    Posts
    1,673
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    i know this an old tbread but, did you ever resolve this issue ?

  3. #3
    Join Date
    Aug 2002
    Location
    Sacramento area
    Posts
    70
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    Thread Starter

    Confused Issue Resolved?

    Quote Originally Posted by coolerinfrederick View Post
    i know this an old tbread but, did you ever resolve this issue ?
    I'll get in touch with my former co-worker (I'm now retired) who was much more involved in this project than I was and possibly send you an e-mail message with more info. But, for a quick answer, the issue was resolved by removing the compressorized chiller from the server room and replacing it with a system using the plant chilled water to cool the R-134a that circulates to the overhead units.

    All of our very knowledgeable & experienced 'super techs' and some of the manufacturer's technicians and representatives and engineers could not determine any other way to resolve the problem, after many, many months of trying.

    So, my user name could be considered misleading, since just 5 years after posting the original post, I'm retired. I retired with 45 years of hands on experience in the field, but continued learning the trade, often feeling like an apprentice, my entire career, even while training new union apprentices.

    All I can say, in all sincerity is, "Good luck; and I feel sorry for you and the owner and users of the equipment."
    I'm still learning this trade.

  4. #4
    Join Date
    Apr 2006
    Location
    mechanical room
    Posts
    1,673
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    well at least they were willing to dump the xdc's, im always learning myself with 17 yrs. experience, heck i just started working on pool equipment which is very unique, some units can have water cooled condensers to heat the pool water, a remote air cooled condenser, a reheat coil and even a hw coil in the rtu, obviously control strategies are very different as well, not only that, every manufacturer has their own controllers and logic

  5. #5
    Join Date
    Jun 2012
    Location
    Northeast
    Posts
    472
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    Did you guys ever have Liebert come out and look? I know load and piping are very critical on these units. I have 4 at one site and never had this problem. Did anyone try to adjust or change the pressure switches? Was it only one of the pumps that did this or both? You had to be losing the liquid seal at the pump.

    I know this was a while ago so if you do not remember I would understand.

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