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  1. #1
    Join Date
    Jul 2011

    Lightbulb Dehumidification Control Help

    Dehumidification Control

    Dear Forum Friends,
    Need advice and have been off awhile with a sick family member. Do a job where there is a humidity controlled space.
    Main AHU has sup humidiity but no dehumidification sequence in place.

    1-So we have Ret Fan Heat Coil, Humidification Bundle, Coil Coil than supply fan.

    2-As you knew we will supply 62F Sup temp in winter mode, and 55F sup temp in summer mode from the AHU to the boxes. VAV's & CAV boxes where they have HW Reheats.

    3-Each JC Stat is reading Temp and Humidity.

    4-We have one wall mounted humidistat.

    The specs show and elect heater will be used for heating and dehumidification control, submittals show heating will be used for heat and dehumidiification.

    But where?
    a) The main air handler unit has the heating coil before the cooling coil so we cannot dehumidify that way.

    b) Would it be at the box zone itself with programming thru the BAS? We have JC Metasys.

    Just wondering, if there should have been an additional heater within the AHU?

    Fear a supply temp reset at the main unit, and waste energy in the space.

    Would welcome anyone's advice and feed back.


  2. #2
    Join Date
    Apr 2012
    Paper Street Soap Company
    What crack addict decided to put the heating coil before the chill cooling coil ??

    If you will undoubtedly have to add electric heaters in the supply ducts.

  3. #3
    Join Date
    Dec 2005
    If the main A/H provides constant temp to the boxes, AND it has fresh air, then the heating coil is before the cooling coil. If not then we will freeze and burst the cooling coil in the winter time.

    Dehum is ALWAYS expensive (no doubt about it).

    In your case you need:

    1) On the main A/H, its supplying temp reset depending on building DB and WB. It can range from wide open CW valve to 68 degrees (or average of zone heating setpoints). IF there is only one humiditat for the whole building then you have no choice but to WIDE OPEN the CW valve when DEHUM is needed.
    2) On the zone, Once the zone statt is satisfied, AND IF the building's DEHUM is still needed, then the box electric heat will stage up to maintain the supply air EQUAL to the room heating setpoint. This way will not have the zone temp - Cold then Hot; Cold then Hot etc..

    Hope it helps you some.

  4. #4
    Join Date
    Jul 2011
    Thx you so much!!!

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