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Humidity control

asked 2017-09-28 02:29:54 -0500

justin gravatar image

updated 2017-10-02 08:14:26 -0500

I am doing a single thermal zone model in Openstudio. I have added a packaged roof heat pump system with an ERV in the air loop. But I don't know how to add humidity control of the HVAC system and then set humidistat.

And I am confused about the difference between "HVAC system" and "zone equipment" in thermal zones tab. As in "HVAC system", we can add different types of equipment, but in "thermal zones", we can also add equipment in "zone equipment". What is the difference between adding equipment in "Air loop" and "zone equipment"

Could anyone help me with these problems?

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answered 2017-10-02 08:40:07 -0500

The difference between the HVAC System tab and the ThermaZone tab has been covered countless times here already. On the HVAC Systems Tab you can define the AirLoopHVAC and the PlantLoop stuff (as well as service water and VRF). On the ThermalZones tab you can see and set the Zonal Equipment. There are cases where a zonal equipment is also on an AirLoopHVAC (that's the case of any of the AirTerminal units) or on a plant Loop (the coils of a Fan Coil Unit for example...). I'm sure you can read more on this by yourself.

As far as implementing humidity control, in EnergyPlus you would use a ZoneControl:Humidistat as well as supporting SetpointMangers (listed and explained in the link I just gave you). I'm telling you this because the documentation from E+ is very informative on the subject, and you should read it.

In OpenStudio, you can set a humidification/dehumidification schedule on the Thermal Zones tab. These expect a schedule of type "Percent" with values from 0 to 100. So head on over to the Schedules tab, and create one or two schedules as you need:

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Then go back to the thermal zones tab, and assign either or both schedules:

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Note that I don't think this object suffers for the same limitation as the thermostat object currently: you can choose to set only humidfication or dehumification if you want, I think (at least the limitation is not on OS side (see forward translator here, but the I/O ref weirdly phrases the single setpoint here...). Anyways, just be safe, and if you only want dehumidification; just assign a humidification schedule with a value of 0, so that there's no humidification happening anyways.

As stated in the E+ I/O ref, you'll need to also assign setpoint managers on your airloop. Here you said you are with a single zone, so let's do this with SetpointManager:SingleZone:Humidity:Maximum and SetpointManager:SingleZone:Humidity:Minimum (which happens to be missing in the 2.3.0 hvac_library, see issue here). You'll want to assign these to the supply outlet node, where you already have a temperature setpoint manager.

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If you want humidification, you'll need a humidifying object... Humidifier:Steam:Electric is the only one available right now since Humdifier:Steam:Gas isn't implemented in OpenStudio yet.

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@Julien Marrec, I have the same doubt. I did exaxtly you recomend, with the same systems, but the output Zone Air Relative Humidity show me that the Relative Humity is free. My setpoint schedule is 55%, and in the output is over 72%. I tryed to add a Dehumidifier DX in the Thermal Zones tab. So this worked. But my system don't have a specific Dehumidifier, I need that the dehumidification would be calculated in the Coil:Cooling:DX. So, do you have some suggestion to correct this? Coil:Cooling:DX can really be analyzed as a dehumidification?

Geraldo Pithon gravatar imageGeraldo Pithon ( 2017-10-02 17:43:37 -0500 )edit

I haven't used dehumidification in OpenStudio really... I'd start by putting the SetpointManager:SingleZone:Humidity:Maximum on the outlet of the DX coil. I would also look at the E+ Example files (eg 5ZoneCoolingPanelBaseboard.idf) to see how it works really, and look at the IDF produced by OpenStudio to see if it matches the pattern or not.

Julien Marrec gravatar imageJulien Marrec ( 2017-10-03 16:51:44 -0500 )edit

Thanks for the reply! I also have the same problem. In the HVAC system, there is no dehumidifier to be selected. So I add an HVAC dehumidifier in "Zone equipment". But there is no information about energy consumption of dehumidification either in OS result or Energyplus result.

justin gravatar imagejustin ( 2017-10-04 03:28:20 -0500 )edit

When you successful setup humdstats, the following variables could be reported: HVAC,Average,Zone Predicted Moisture Load Moisture Transfer Rate [kgWater/s],HVAC,Average,Zone Predicted Moisture Load to Humidifying Setpoint Moisture Transfer Rate [kgWater/s],HVAC,Average,Zone Predicted Moisture Load to Dehumidifying Setpoint Moisture Transfer Rate [kgWater/s]. For HVAC system, you need to have 2 Stage dehumidifying DX coil or Cooling water coil to get it works.

ngkhanh gravatar imagengkhanh ( 2017-10-05 23:55:05 -0500 )edit

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Asked: 2017-09-28 02:29:54 -0500

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Last updated: Oct 02 '17