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  1. #1
    Join Date
    Jan 2007
    Location
    Charm City--the city that bleeds
    Posts
    2,790

    question about a new economiser package on old RTU

    We were subbed to install some new HWL parts on an old Mc Quay RTU. The RTU is controlled by a KMC controller. We were supplied with the following parts: W7459A econ logic module, an M7415 damper actuator, a C7046A air temp sensor, and two C7400A enthalpy sensors.
    Also we have a C7150B temp sensor, but haven't used it ....yet.
    Installed those parts other than the C7150, using the C7046A as the discharge air temp sensor. Placed one of the C7400s in the OA air hood, and the other about midway along in the RA inlet
    powered the economiser package with the original XFMR, and broke it through a control relay which is energized when the KMC controller calls for Economiser (which then energizes the RTU terminal D).
    This appears to be setup for what is called differential enthalpy.

    At this point when a jumper is placed from R to Y1 the compressors are energized, but the 24 volts from D, or economiser goes away and the actuator is not energized. The spring returns it to 100% RA, 0% OA, and the Y1 cooling happens. At the end of this call for Y1, the 24 V returns to the D terminal, so then the economiser functions at minimum position.

    So I said all that to say this...
    Will it be best to continually power the econ package with 24V, and then place it in the lead at Y1?
    That is the goal of the install job, so we may have to reconfigure one or two things on the KMC panel, no?

    Any recommendations for a differential enthalpy setup?
    It's great to be alive and pumping oxygen!

  2. #2
    Join Date
    Dec 2005
    Location
    Spokane Wa
    Posts
    169
    fan circuit should power econimizer module (tr & tr+). y1 circuit from stat connects to #1 on module

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