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    Modulating dampers and controls for HVAC (7 Posts)

  • BWeaver BWeaver April 19, 2011 @ 3:47 PM
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    Modulating dampers and controls for HVAC

    Is there a control out there that will handle up to 20 or 30 zones with modulating dampers?
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  • Tim Tim April 19, 2011 @ 4:18 PM
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    A Trane VariTrac

    system based on a Central Control Panel (CCP) will communicate with up to 24 VAV unit control modules.
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  • Brad White Brad White April 23, 2011 @ 6:14 PM
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    If

    you are going to have that many zones, I would recommend a static pressure controlled VFD for the fan to allow the airflow rate to back off as dampers start to close. VAV is an excellent energy saver and for a system of this presumed size, would add value.

    My $0.02 anyway.
    "If you do not know the answer, say, "I do not know the answer", and you will be right!"
    -Ernie White, my Dad
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  • tim smith tim smith April 29, 2011 @ 8:55 AM
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    Re: What Brad said

    I agree Brad, I did one of these on this big mansion that had a huge old Trane belt drive air handler. Installed vfd and new 3 phase motor. Static pressure transducer and just dialed in. Quite cool except adjusting out harmonic noise was a bit trying. Tim
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  • John Mills John Mills April 29, 2011 @ 9:55 AM
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    20 zones

    http://jacksonsystems.com/view_product/24978
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  • Techman Techman April 30, 2011 @ 10:57 AM
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    Carrier

    has a 3V system,they do Disneyland & the U.N. building.I am not familiar w/ the system that Brad suggested.
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  • Brad White Brad White April 30, 2011 @ 4:18 PM
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    The system I described

    is generic VAV control, most often done in buildings with DDC systems.

    The basic premise is that all terminal boxes (VAV boxes, dampers or air valves) are pressure-independent. In other words, they compensate for variations in system supply duct pressure to maintain the CFM they need to deliver at that moment. Secondly to that, the supply duct system has a pressure transducer or several of them in critical branches, to measure the duct static pressure at fairly remote points in the system. The transducers send back an analog signal to the DDC system which in turn controls the supply fan speed, usually via a variable frequency drive (VFD), operating the fan.

    As the VAV boxes throttle down, the duct pressure rises. In order to keep this constant, the VFD slows down the fan to keep the pressure constant. You can imagine if it is evening and 80% of the boxes are turned down to 20%, it will take very slow fan speeds to maintain that pressure. Even a 20% drop from a peak load will need only 51% of the full fan HP.  Significant energy savings are to be had here.

    A refinement of the above is to re-set the duct static pressure setpoint downward at low load periods. Even more savings.
    "If you do not know the answer, say, "I do not know the answer", and you will be right!"
    -Ernie White, my Dad
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