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OpenStudio Humidity Setpoint Not Met

asked 2016-06-30 14:31:29 -0600

updated 2017-05-17 12:20:55 -0600

Dear Modeling Community,

I have setup humidification and dehumidification setpoint schedules of always 35% and 70%, respectively. However, when checking the Zone Conditions Humidity table there are significant hours (~3750 hours) where the humidity is below 30%. This is strange because based on the setpoint the zone should not be allow to drop below 35%.

For context, the project is a Midrise Apartment so the occupancy doesn't drop down like office. I would suspect humidification to be necessary throughout most of the day.

I am using a PTHP, could it be that the system does not have any humidification/dehumidification functionality so although I have a schedule set there is no control to the humidity?

Any other suggestions why the humidity is uncontrolled in my space, despite defining setpoint schedules would be very appreciated.

Thank you, Justin

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answered 2016-07-01 08:45:53 -0600

In E+, in order for the humidity to be controlled you need several things:

  1. A ZoneControl:Humidistat with humidity setpoint schedules.
  2. For humidification you need a humidifier of some sort. OS has the Humidifier:Steam:Electric object which must be added to an AirLoop. To you use this object you'll also need to put a SetpointManager:Humidity:Minimum, a SetpointManager:MultiZone:HumidityMinimum, or a SetpointManager:MultiZone:MinimumHumidityAverage on the Outlet Node of the Humidifier:Steam:Electric. Check out the Input-Output Reference to understand which one fits your situation.
  3. For dehumidification you need a system that can control humidity. Not all HVAC systems in E+ (or reality) control humidity explicitly. Here is a non-exhaustive list of some options:

    1. A ZoneHVAC:Dehumidifier:DX
    2. A Coil:Cooling:Water with the Controller:WaterCoil 'Control Variable Field' set to 'TemperatureAndHumidityRatio'
    3. An AirLoopHVAC:UnitarySyste with the 'Dehumidification Control Type' field set to 'CoolReheat' or 'Multimode'.
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Also, see this issue, which affects the humidity SPMs.

MatthewSteen gravatar imageMatthewSteen ( 2016-07-01 10:20:33 -0600 )edit

@aparker Thank you for your response. I found it very helpful but I'm having a bit of trouble. I have set up an custom air loop with an OS:Fan:VariableVolume, OS:Humidifier:Steam:Electric, and OS:SetpointManager:MultiZone:Humidity:Minimum on the Supply side and on the Demand is all the zones. However, when I run the file I get the error AirLoopHVAC="AIR LOOP HVAC 1" has no Controllers and An outlet node in AirLoopHVAC="AIR LOOP HVAC 1" is not connected to any zone. Any idea how to fix this error? I haven't been able to figure out how to add a ZoneControl:Humidistat in OpenStudio?

JustinShultz gravatar imageJustinShultz ( 2016-07-06 10:26:14 -0600 )edit

You add the humidistat by specifying humidity schedules on the ThermalZones tab. I'm not sure what the cause of the errors is. I assume you did not modify the .osm by hand in a text editor?

aparker gravatar imageaparker ( 2016-07-06 11:35:41 -0600 )edit

@aparker thank you for your quick response. I have specified humidity schedules (as percentages) on the ThermalZones tab. Maybe it would be easier with images of thermal zones and system configuration

JustinShultz gravatar imageJustinShultz ( 2016-07-06 12:18:58 -0600 )edit

Your AirLoop doesn't have an OA intake, so if your zones do have Designspecification:OutdoorAir objects assigned this could be the root of the error. Basically, the zones are requesting OA but there is no way for them to get OA. Check out cause #2 in this answer

aparker gravatar imageaparker ( 2016-07-06 13:03:44 -0600 )edit

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Asked: 2016-06-30 14:31:29 -0600

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Last updated: Jul 01 '16