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  1. #1
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139

    Room Temp/Humidity Control Sequence

    Does anyone have and is willing to share some logic or a sequence that basically incorporates humidity in a zone and adjusts the room set point depending on the humidity? Basically I have this reoccurring problem where a user constantly adjusts the room set point because of comfort and the issue is not temperature but the changing humidity levels.

    Thanks.

  2. #2
    Join Date
    Oct 2007
    Location
    England
    Posts
    221
    I'm sure many would be able to help here, but what line of controls are you talking about?

    You need to describe what inputs and outputs you have.

  3. #3
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139
    The control line is Alerton and the units are fan coils with modulating chilled water, hot water, economizer. I was speaking more generally about this issue since I see this problem with many jobs in the past.

  4. #4
    Join Date
    Apr 2008
    Location
    chicago
    Posts
    115
    Is hot water available year round? Is hot water coil after the cooling coil?

  5. #5
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139
    The chilled coil is after the heating coil. Im not really looking for a dehumidification sequence, what I am looking for is a control algorithm that adjust zone temp set point when the space humidity increases or decreases, to anticipate comfort levels.

  6. #6
    Join Date
    Oct 2007
    Location
    England
    Posts
    221
    I would have thought that Alerton have some sort of 'Reset' block or code.
    i.e. when input is at level 'a' then output = x
    when input is at level 'b' then output = y
    any input between a or b = a proportional output value of x to y
    Last edited by Keith D; 06-19-2014 at 08:08 PM. Reason: im just old and confused

  7. #7
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139
    Yea they do but I'm looking for something more than a straight linear converter. I don't know if anyone else has considered this, that's what prompted me to post here

  8. #8
    Join Date
    Jan 2003
    Location
    USA
    Posts
    1,770
    I don't think mind readers have been wrapped up in a software module yet.

    Try the straight line, but I think your chasing the impossible much past that.
    Propagating the formula. http://www.noagendashow.com/

  9. #9
    Join Date
    Apr 2008
    Location
    chicago
    Posts
    115
    It could be that your system is just not sized properly. The discharge from the unit to maintain space temperature may not be cold enough to provide adequate dehumidification. It sounds like you are trying to fix a mechanical design issue with controls.

  10. #10
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139
    Ok so here is where I got the idea from,

    The new Honeywell thermostat Lyric supposedly has some feature that it will self-adjust the temperature based on the relative humidity. I guess they did some research and found that most temperature adjustments made by occupants are driven by comfort levels associated with increases or decreases of humidity. I do this at my house all the time. I am trying to see if anyone has translated this strategy to the DDC world.

  11. #11
    Join Date
    Jan 2003
    Location
    USA
    Posts
    1,770
    Keep in mind there is a huge difference between marketing wank, and the real math behind what its doing.

    If you lower space temp, you most likely just increase RH.

    Every mechanical fail cannot be corrected by fancy controls.
    Propagating the formula. http://www.noagendashow.com/

  12. #12
    Join Date
    Jun 2006
    Location
    Mount Airy, MD
    Posts
    90
    Fisha,
    Sizing of Systems are critical so that the Cooling is On for longer periods of time, which will remove the humidity from the air as condensate.

    Changing Setpoints of the Room Temp up and down are not the solution, because that method will always make the Space uncomfortable before it becomes comfortable, as your Room Temp will swing outside of the allowable max of a 2.0 F range. The reason the System works to dehumidify, is basically because you are causing the Cooling to run or open for the longer period of time needed to dehumidify the Air.

    Other than Correct Design, the only way to dehumidify is to Reheat the Air, while the Cooling Valve is fully open.

    One more critical piece of info, is that the Chilled Water Supply must be set at 42.0 deg F.

    Sounds like your Home unit is sized incorrectly as well.

    Old Rule; "Engineers are always right"
    New Rule; "You had better check on their Design, because they no longer perform Lessons Learned on their previous Designs"
    "Please, Do Not Shoot the Messenger!!!"


    "It is not what you Know, but rather, Knowing where to find the answer when you need it"

  13. #13
    Join Date
    Mar 2014
    Location
    Pittsburgh, PA
    Posts
    139
    My home unit is not oversized. Nor is the other units I am speaking.

    Maybe Honeywell is on to something, I will see what else comes out of this.

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