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  1. #1
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    Digital Scroll modulation with DAC/VAV Aaon RTU

    Hey programming gurus,

    On a Aaon VAV RTU with 2 compressors, 1 digital scroll, 1 fixed capacity, do you include the suction pressure transducer for control? I realize that I could use it to calculate evaporating temp, but why would I?

    I'm modulating the scroll based on SAT. When the C-PID is >55% I start DX stage 2 and send stage 1 modulation back to minimum and increase the DX1 mod to 100% as the c-PID reaches 100%.

    Would it be prudent to include the suction pressure as a safety/ variable high limit to prevent the coil from freezing should it ever fall below 101 psi (r410a).

    Does anyone have an application guide for this? Pretty sure it's not covered in the Gray Manual!

    Thanks

  2. #2
    Join Date
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    Fort Worth\Dallas, Texas
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    Thats pretty much what I have done in the past. If it has the Copeland compressor module for the digital scroll I believe you have to send a minimum of like 1.2 volts to the module for the compressor to run.
    Go Rangers!

  3. #3
    Join Date
    Apr 2014
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    The suction pressure works for dehumidification pretty well. You can control for pressure to get max cooling to wring out moisture, then reheat as needed.

  4. #4
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    First time I've heard of this, why would you take control of the digital scroll away from the unit's control? What level of better efficiency/operation is achieved?

  5. #5
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    To clarify- are you doing this through a BMS system or is this something that is programmed in the Aaon controls?

  6. #6
    Join Date
    Apr 2014
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    Quote Originally Posted by RezAtDorsia View Post
    To clarify- are you doing this through a BMS system or is this something that is programmed in the Aaon controls?
    Many Aaon's are "controls ready" so all the devices are broke out on a terminal block and you install the controller of your choice.

  7. #7
    Join Date
    Jul 2014
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    It min 1.44 vdc . Hot gas reheat is on circuit 1 and if your in dehumid and compressor at 10 percent good luck reheat

  8. #8
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    Jul 2014
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  9. #9
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    Jan 2007
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    Suction pressure is used to maintain 40 to 45 evap during dehumidification. Does the unit have dehumidification?
    ckartson
    I didn't write the book I just read it!

  10. #10
    Join Date
    Apr 2010
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    The unit does not have hot gas reheat. The heating section is indirect fired modulating gas.

    There is no unit controller, which is why this post in the controls section.

    I was simply curious about how others are staging a unit like this. Thanks to JCIman and lwarren for your input.

  11. #11
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    Apr 2010
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    Quote Originally Posted by Gp71 View Post
    GP71,
    Thanks for your input. It makes sense to keep the compressor above 70% to maintain reheat for dehum mode. Unfortunately I don't have reheat on this unit which I guess I didn't really mention in the OP. I'll keep that in mind though if I ever get involved with a unit with reheat and there's not a factory controller.

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