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  1. #1
    Join Date
    Oct 2007
    Location
    Arizona DUH
    Posts
    174

    Trane varitrane reheat problem

    I am working in an office building that has all Trane VAV boxes with series fans and hot water re-heat coils (comm 4 boards). All of the rooms in tracer are set at 72 cooling and 70 heating (about 15 rooms). There are around 6-8 offices that are 74 cooling and 72 heat. All of the rooms today were running anywhere from 2-3 degrees below heating setpoint. It was 45 outside, the AHU was putting out 55 degree discharge air, and all of the vav's air valve was around 26% open pushing each at around 350 cfm. Here in lies my dilemma, the discharge air on most of these boxes was only 69-72 degrees. The box air valves said they were in cooling mode. The AHU does have a cooling (55) and Heating (100) setting on the DAC profile but it always is at 55-56 degrees. I manually raised the active setpoint to 60 and the box temp rose a little. I went into summit and picked a few boxes and vent to the VAV controller editor and clicked to run the hot water valves to full open and the discharge air went to 94 degrees. FINALLY my question, why if the room temp is 2-3 degrees or more below the active heating setpoint and the box in summit says heat is active, it appears my valves are not opening far enough to heat the space. WHY????? Our company does not have that rover software and we do most basic stuff in summit, is there any way to change the proportion of the valve to open more closer to setpoint? I could under stand not blowing the valve to 60-70 percent within 1-2 degrees but at 2-3 degrees I am not raising my discharge higher than the room temp. Any idea's.

  2. #2
    Join Date
    May 2007
    Location
    Pacific Northwest
    Posts
    38

    Actuator Timing Issue?

    Sounds like it could be an actuator stroke time issue to me. The HW valve actuators should be the type that are drive-open/drive close. When this is the case the UCM needs to know how long it takes to stroke the actuator from fully closed to fully open. If the time value is wrong in the UCM then it doesn't really know what position the valve is actually at. When you override the valve to OPEN then it will drive the valve open for the actuator stroke time regardless of current position. This could explain why you saw what you did.

    The other thing that could cause this is that the UCM needs to be recalibrated. When time-based positioning is used, as in this situation, the actual position of the actuator and where the UCM thinks it is can become out of whack. When the VAV UCM is sent into recalibrate mode, one of the things it does is drive the HW valve closed for the actuator stroke time + 15 seconds to establish the closed position. You should already be recalibrating the VAV boxes periodically so this may not be the issue. If this was this case I wouldn't think you would be seeing it in nearly every box.

    I would check the HW valve stroke time compared to what the actuators actual time is and go from there.

    Knobber

  3. #3
    Join Date
    May 2007
    Posts
    73
    Quote Originally Posted by Knobber View Post
    You should already be recalibrating the VAV boxes periodically so this may not be the issue. If this was this case I wouldn't think you would be seeing it in nearly every box.

    I would check the HW valve stroke time compared to what the actuators actual time is and go from there.

    Knobber

    Just so you know, I have seen many of these systems do this when there is no recalibration schedule. The stroke time is also a good thing to check....but, you should schedule a recalibration time for say Sunday night at 2:00 a.m.

  4. #4
    Join Date
    Oct 2007
    Location
    Arizona DUH
    Posts
    174

    ;o)

    I do have a recalibrate schedule in there once a week at 2:00 am.

    I will check but I am sure all of the valves that trane put in are 90 seconds.

  5. #5
    Join Date
    Nov 2004
    Location
    Practically Canadian ehh.
    Posts
    675
    What is the Heat Type configured on the Vav editor in Summit?

    What model actuators you have?

  6. #6
    Join Date
    Oct 2007
    Location
    Arizona DUH
    Posts
    174
    proportional hot water

    they are belimo actuators 90 second drive time

  7. #7
    Join Date
    Nov 2004
    Location
    Practically Canadian ehh.
    Posts
    675
    Quote Originally Posted by buckeye Fitter View Post
    proportional hot water

    they are belimo actuators 90 second drive time
    What model are the Belimo's? Importantly the latter digits US or US-3?

  8. #8
    Join Date
    Oct 2007
    Location
    Arizona DUH
    Posts
    174
    I will find out on Monday

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