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  1. #1

    Liebert Mini-mate temperature and humidity fluctuations

    I have a dual Liebert Mini-Mate 2 2 ton setup in a 25'x25' room with 18' ceilings and the units alternately operating on 7 day cycles. It is an art storage room that is fully encased in concrete/cinder block with epoxy wall and floor coating. The set points are 70deg w/1deg diff and 50% hum w/1% diff due to the critical nature of the room contents. We have had a consistent issue with temperature and humidity fluctuations and the units taking a long time (8+ hours) to balance out. The room gets very little traffic and at the moment no fresh air intake. The room will be balanced and holding at the set points for a few hours then all of the sudden at random the temperature will drop 3 to 4 degrees. The heater will then kick in and the humidity spikes thus activating the dehumidification. This will cycle up and down for hours on end before eventually balancing out and holding for a couple of hours. We have tried adjusting set points, fan speeds, calibrating sensors, absolute and RH modes all to no avail. I am beginning to think the room is haunted. Any thoughts? Thank you.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,260
    That kind of variation is to be expected from the system you have. The problem is the moisture left on the cooling coil at the end of dehumidifying cycle. You unit is trying.
    Add a ducted dehumidifier like a Ultra-Aire whole space dehumidifier with a sensitive dehumidistat to narrow band control.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    That sensativity set points are very tight. The temp set point is low and rh is high. With no real room load, you need to balance the units with the sensativity. With all concrete walls, that adds to your load change. The controller for these units ignore's temperature when in dehum, therefore the reason for temperature drop. Heat load would help with this but art does not produce heat. The sensativity so tight will not allow the unit to produce properly. With 1% on humidity, the unit with go into dehum at 51% and cycle dehum off at 49%. All this will do is keep repeating itself and never achive satisfaction. Please keep in mind the room really needs to be designed for 50% RH. Most data rooms cannot achieve it do to poor room canditions. You need to add some dead band to these units. If you want 50% RH, you might try sensativity at 5%(Default) or 3-4%. Unit will go into dehum at 55% and cycle off dehum 45%. What is the recommended room settings for the art?

    Are these units DX or Chilled water?

  4. #4
    Join Date
    Jul 2003
    Location
    Massachusetts
    Posts
    288
    yea I recently dealt with this type of issue where I was focusing too much on the cooling setpoint, and the humidity setpoint was dragging the temp down too much and enabling heat. I would do everything that Liebert_tech suggests. because his name is Liebert_tech after all.

  5. #5

    Liebert Mini-mate temperature and humidity fluctuations

    Jacobk - I have almost the identical setup and issue you described. Were you able to resolve your issues? I have recorded the RH and Temperature for a 2 week period (a record every minute). What I found was that the system maintained RH and temp. till the AC kicked in. My set point is 20 degrees C +- 2 and 50% RH +- 6%. At this setup the unit cycles every 15 minutes. To me this is excessive and I'm concerned this will lead to premature wear.

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