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  1. #1
    Join Date
    Dec 2006
    Location
    Boston area
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    243

    Trane CGAM issue

    Have a new installation and the piping is ran on the roof, appx 300' supply and return. Issue I'm having is chiller shuts down on-Chilled water flow Entering Water Temp. I have the chiller controlling my chiller pumps. I figure when main CW loop is satisfied chiller shuts off pumps and even though pipe is insulated it is still being effected by outdoor temp and gets colder than chiller setpoint. The heat tape on chiller barrel causes temps. To read well in excess of 160 degrees. Spoke to Trane support and they say that is normal. They also said to added a bypass control to keep pumps running, I did that but the chiller will still go into same alarm and it is not an auto reset alarm so eventually pump shuts down. Problem should go away for season as it is getting warmer outside but I know it will happen again. Wondering if anyone has seen similar issue and how it was resolved.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
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    4,386
    don't let the chiller control the pumps or put in a timer that keeps the compressors off for 5 or 10 minutes or something after the pump starts.
    When I am late for work, I usually make up for it by leaving early.

  3. #3
    Join Date
    Mar 2009
    Location
    Mid-Mo
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    3,595
    Is there a ddc system in place here?

    I'm not super familiar with these machines but jay, what's the problem with the chiller controlling its own pump?

  4. #4
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
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    4,386
    Quote Originally Posted by ryan1088 View Post
    Is there a ddc system in place here?

    I'm not super familiar with these machines but jay, what's the problem with the chiller controlling its own pump?
    just in this case....and in similar cases. he is experiencing a situation where the chiller is seeing colder water enter the evaporator due to outside forces (idle solution in cold weather, etc.). the chiller is not setup to handle a situation like this. i have encountered situations like this with a large chiller/small chiller setup. when the big chiller over cools and the BAS switches to the small chiller, the small chiller begins its start up too quickly and the entering water temperature from the very cold loop hits the warm barrel....chiller trips. by the time i get there, the loop has warmed up and it works just fine. in the older chillers, you could add a resistor to the entering chilled water temperature sensor to raise displayed water temperature a few (or a lot) degrees higher than actual to get over the hump and get things going....but not with the newer models unless you want to break into the LLID (which i have seen done before...not recommended).

    adding a timer or delaying the chiller startup after a period of time is the simplest method of correction. even if the chiller has no intention of starting a compressor, it still compares the entering and leaving water temperatures when the chiller gets enabled.
    When I am late for work, I usually make up for it by leaving early.

  5. #5
    Join Date
    Feb 2013
    Location
    Phoenix, AZ
    Posts
    198
    If you do have a DDC system in place, start the pump first, let the building load warm the loop up to normal temps, start the chiller when the entering chw temp is warm enough not to cause a trip (maybe a couple degrees above setpoint?). You can leave the sequence in year-round, because when the weather is warmer the water will start out warm enough and will start the chiller without delay.

  6. #6
    Join Date
    Mar 2007
    Posts
    3,108
    Seems to me like if the chiller has a start command and is in local mode "auto", the pump should be running regardless of the loop temperature. If the loop is below setpoint, the chiller should display "waiting for need to cool". The load from the building and the pump itself will heat the water up enough eventually to start the chiller.

    This sounds to me like when the loop is satisfied, the OP is somehow losing the start command to the chiller. If the loop is satisfied, he still needs to maintain the start command. Pump needs to be running at all times when you could reasonably expect the chiller to be cycling on and off, i.e. when the space is occupied.

    Two other things to look at are what the actual delta T is in the system versus what is programmed into the MP and the chilled water setpoint... Maybe you could get away with a few degrees higher to keep the machine running?

    I think faking out the return water temp sensor wouldn't be a real good idea with this one because the CGAM looks at return water temp also to anticipate changes in the load (this is called "feed-forward" with their other machines) and to estimate tonnage needed based on the chilled water delta T.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  7. #7
    Join Date
    Jul 2008
    Location
    NEW JERSEY
    Posts
    40
    What type of solution are you using?

  8. #8
    Join Date
    Mar 2010
    Location
    Va.
    Posts
    180
    The CH530 is setup for freeze protection by default. You can get high chill water temperatures if the pump is running in freeze protection and the chiller is unoccupied. You could be getting the Low Entering Temperature alarm if it is operating in this condition.

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I'd just keep the pump running. I personally don't like to rely on heat trace to avoid a lot of frozen piping. I consider tracer a good back-up if the pump fails in winter. Since its' traced, the cost to operate the pump will be negligible sicne the pump will heat the water a little instead of the heat trace. You adding heat to the system either way. You could always add a VFD and preset 2 speeds for the pump and have the chiller trigger the higher speed.

    But I agree, if the chiller is in auto, then the leave the pump running.

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