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DesignSpecification:OutdoorAir for PTAC [closed]

asked 2023-11-07 12:02:42 -0500

IanVG's avatar

updated 2023-11-08 07:11:20 -0500

I am trying to use OpenStudio and EnergyPlus to model the internal sensible and latent loads for a building. EnergyPlus will output all sensible loads fairly easily, but it's a different story for internal latent loads (in my situation almost exclusively people). From hours of digging it looks like using a 'dummy zone equipment', for example a PTAC (specifically a Cycling PTAC DX Clg Elec Htg object) is the best way to get access to the latent load. It looks like I am getting some latent loads with this. Success. Since I've included infiltration into the model I'm sure that this latent load also includes infiltration. That's fine, I can take out infiltration when I need to.

However, now I'd like to add in the latent load due to outdoor air flow. I see the three objects that can control outside air, but based on this section of the Input - Output documentation I was expecting an option somewhere for the Field: Outdoor Air Method, but I cannot find it. I'd like to know how the outdoor air flow is being autosized for this zone through the PTAC. Any suggestions?

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Closed for the following reason the question is answered, right answer was accepted by IanVG
close date 2023-11-07 17:17:27.277158

1 Answer

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answered 2023-11-07 12:28:14 -0500

updated 2023-11-07 12:29:11 -0500

In the zone sizing object, Sizing:Zone, there is an input for the zone design outdoor air flow rate. The PT unit in that zone, if it has an OA mixer, will size the outdoor air flow rate to meet the OA flow specified in the DesignSpecification:OutdoorAir object.

  WEST ZONE,               !- Zone or ZoneList Name
  SZ DSOA WEST ZONE,       !- Design Specification Outdoor Air Object Name

  SZ DSOA WEST ZONE,       !- Name
  flow/person,             !- Outdoor Air Method
  0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
  0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
  0.0;                     !- Outdoor Air Flow per Zone {m3/s}

  Zone3PTHP,               !- Name
  FanAndCoilAvailSched,    !- Availability Schedule Name
  Zone3PTHPAirInletNode,   !- Air Inlet Node Name
  Zone3PTHPAirOutletNode,  !- Air Outlet Node Name
  OutdoorAir:Mixer,        !- Outdoor Air Mixer Object Type
  Zone3PTHPOAMixer,        !- Outdoor Air Mixer Name
  autosize,                !- Cooling Supply Air Flow Rate {m3/s}
  autosize,                !- Heating Supply Air Flow Rate {m3/s}
  autosize,                !- No Load Supply Air Flow Rate {m3/s}
  autosize,                !- Cooling Outdoor Air Flow Rate {m3/s}
  autosize,                !- Heating Outdoor Air Flow Rate {m3/s}
  autosize,                !- No Load Outdoor Air Flow Rate {m3/s}
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Thanks! I have no idea how to find the Sizing:Zone object in OpenStudio. I have my design days file imported and all the appropriate Do * Sizing parameters turned on; I still cannot find the Sizing:Zone object. any tips?

IanVG's avatar IanVG  ( 2023-11-07 13:11:14 -0500 )edit

Ok, it looks like I can add a natural ventilation object to the zone. Is that the right solution?

IanVG's avatar IanVG  ( 2023-11-07 13:41:36 -0500 )edit

"The PT unit in that zone, if it has a OA mixer..." How do I ensure that the PTAC has a OA mixer in OpenStudio? I cannot find any parameter that indicates that the PTAC can have a OA mixer.

IanVG's avatar IanVG  ( 2023-11-07 13:42:48 -0500 )edit

Okay, I found that when in OpenStudio under the HVAC Systems tab and for any added AirLoop system, when I click on the dashed line, there is a parameter under OS:Sizing:System for System Outdoor Air Method. However for the zone itself, there is no parameter under OS:Sizing:Zone for System Outdoor Air Method. This is confusing the heck out of me.

IanVG's avatar IanVG  ( 2023-11-07 13:56:07 -0500 )edit

Even more discoveries. Looks like in the Space/Properties/Airflow section in OpenStudio, there is a parameter for the Design Specification Outdoor Air Object Name. Maybe this space property is driving the PTAC OA auto-sizing calculation?

IanVG's avatar IanVG  ( 2023-11-07 14:06:26 -0500 )edit

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Asked: 2023-11-07 12:02:42 -0500

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Last updated: Nov 07 '23