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  1. #1
    Join Date
    Jun 2006
    New Jersey

    Trane Varitrac CCP

    Got a building with a couple Varitrac CCP's. They are CV RTU's with bypass dampers. The one thing I just can't grasp is how the static pressure setpoint is derived. I see a system setpoint multiplier, but how does that derive my static setpoint of 0.50" on system 1 and 0.86" on system 2?

  2. #2
    Join Date
    Feb 2005
    I forget the exact sequence but the gist of it is that every time the system goes from unocc to occ, the ccp forces all the boxes to a certain % and measures what max pressure the system/RTU is capable of achieving and that becomes your setting.

    Edit, ok I found ccp manual online and here is a copy of the exact sequence for static pressure setpoint:

    For the CCP start-up sequence to begin, it is necessary for one UCM and a
    communicating sensor/bypass control on the loop to communicate with
    the CCP.
    • The CCP prepares for static calibration.
    • UCMs begin driving closed to perform their calibration reset.
    • After calibration, the UCMs are driven to maximum position, and the
    bypass begins to close.
    • The “zero flow” voltage reading is taken with the fan off.
    • System fan is turned on for approximately 45 seconds.
    • High flow static sensor voltage is taken and stored in the CCP.
    • The bypass damper is then driven to 50 percent and released.
    • The UCMs are released from their MAX flow position.

  3. #3
    Join Date
    Jun 2006
    New Jersey
    Cool thanks. But do you know where system setpoint multiplier comes into play. For example the default is 1.4.

  4. #4
    Join Date
    Feb 2005
    Looks like it is a way for you to massage the setpoint to what you want. That is, to a certain degree from the measured static during calibration, read this:

    Static Pressure Bypass
    The VariTrac CCP controls the bypass damper(s) using measured duct static
    pressure. The central control panel compares the measured static pressure to the
    setpoint. This setpoint is determined by taking the reference static determined
    during calibration, and multiplying it by the static-pressure-setpoint multiplier
    percent edited in CCP Setup.
    If the measured static is lower than the static pressure setpoint minus 10
    percent, the bypass damper is driven towards the closed position.
    If the measured static pressure is greater than the static pressure setpoint, the
    bypass damper is driven towards the open position.
    The bypass damper remains stationary if the static pressure is in the deadband.
    The deadband is the area between the static pressure setpoint and the static
    pressure setpoint, minus 10 percent.
    The bypass damper can be repositioned up to four times per minute. When the
    bypass damper is repositioned open, it moves 8 percent each time. When the
    bypass damper is repositioned closed it moves 5 percent each time.
    If the static sensor fails, the bypass damper is driven to the fail-safe position of 50
    percent and the system continues to operate.
    When the zone is unoccupied, the bypass damper is driven to 50 percent.

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