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Can the Duct E+ object be used to make a AirLoop demand-side bypass?

asked 2017-05-04 18:56:44 -0500

NickC's avatar

updated 2023-04-12 16:40:16 -0500

How is the E+ Duct Element typically used? I was contemplating using it as an Airloop demand bypass, similarly to a plant demand bypass with an adiabatic pipe. Tried to add it in between an exiting AirLoopHVAC:ZoneSplitter and AirLoopHVAC:ZoneMixer objects, but got yelled at by E+.

AirLoopHVAC:ZoneMixer,
  AHU-1 Return Air Mixer,            !- Name
  AHU-1 Zone Equipment Outlet Node,  !- Outlet Node Name
  AHU-1 Inlet Node TZ01-11,          !- Inlet 1 Node Name
  AHU-1 Inlet Node TZ01-12,          !- Inlet 2 Node Name
  AHU-1 Inlet Node TZ01-13,          !- Inlet 3 Node Name
  AHU-1 Inlet Node TZ01-21,          !- Inlet 4 Node Name
  AHU-1 Inlet Node TZ01-22,          !- Inlet 5 Node Name
  AHU-1 Inlet Node TZ01-23,          !- Inlet 6 Node Name
  AHU-1 Inlet Node TZ01-24,          !- Inlet 7 Node Name
  AHU-1 Inlet Node TZ01-25,          !- Inlet 8 Node Name
  AHU-1 Inlet Node TZ01-26,          !- Inlet 9 Node Name
  AHU-1 Inlet Node TZ01-31;          !- Inlet 10 Node Name
  AHU-1 Inlet Node Bypass;           !- Inlet 11 Node Name

AirLoopHVAC:ZoneSplitter,
  AHU-1 Supply Air Splitter,        !- Name
  AHU-1 Zone Equipment Inlet Node,  !- Inlet Node Name
  AHU-1 Outlet Node TZ01-11,        !- Outlet 1 Node Name
  AHU-1 Outlet Node TZ01-12,        !- Outlet 2 Node Name
  AHU-1 Outlet Node TZ01-13,        !- Outlet 3 Node Name
  AHU-1 Outlet Node TZ01-21,        !- Outlet 4 Node Name
  AHU-1 Outlet Node TZ01-22,        !- Outlet 5 Node Name
  AHU-1 Outlet Node TZ01-23,        !- Outlet 6 Node Name
  AHU-1 Outlet Node TZ01-24,        !- Outlet 7 Node Name
  AHU-1 Outlet Node TZ01-25,        !- Outlet 8 Node Name
  AHU-1 Outlet Node TZ01-26,        !- Outlet 9 Node Name
  AHU-1 Outlet Node TZ01-31,        !- Outlet 10 Node Name
  AHU-1 Outlet Node Bypass;         !- Outlet 11 Node Name

Duct,
  AHU Demand Bypass Duct,   !- Name
  AHU-1 Outlet Node Bypass, !- Inlet Node Name
  AHU-1 Inlet Node Bypass;  !- Outlet Node Name

************* Beginning System Sizing Calculations
** Severe  ** Node AHU-1 OUTLET NODE BYPASS connects to no component
**   ~~~   ** Occurs in Supply Air Path=AHU-1 SUPPLY AIR PATH
**   ~~~   ** Check the connection to a ZoneHVAC:EquipmentConnections object
**   ~~~   ** Check if this component is missing from the Supply Air Path
**  Fatal  ** Preceding errors cause termination

Thanks

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answered 2017-05-05 12:18:52 -0500

updated 2017-05-05 12:19:01 -0500

There are a couple example files that use the Duct object, I would start there to see how it's used:

  1. 5ZoneSupRetPlenRAB.idf (looks like this one uses the Duct as a bypass).

  2. DOASDualDuctSchool.idf

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Thanks @Eric Ringold; I looked at the two IDFs you mentioned. Seems that the Duct object is used as a component on the AirLoop supply side in both instances. I'm interested in making a demand-side bypass, similarly to a bypass adiabatic pipe on CHW PlantLoop (with a constant speed supply pump)

NickC's avatar NickC  ( 2017-05-05 14:24:38 -0500 )edit

OK, admittedly I didn't dive too deep into those files. It does seem like using it for a demand bypass would be allowed per the I/O ref. Are you sure you had it set up correctly (with required Branch objects, etc) when the program yelled at you? (PS - posting the actual error message is always helpful).

ericringold's avatar ericringold  ( 2017-05-05 14:28:16 -0500 )edit

Agreed, seems like it should be allowed from the IO ref. I added some flavor text to the post! Think I set it up correctly, but probably not...

NickC's avatar NickC  ( 2017-05-05 17:57:02 -0500 )edit

I'm curious if this was ever resolved? I'm currently struggling to find a reasonable way to account for a demand-side bypass.

jt1234's avatar jt1234  ( 2018-09-21 09:59:26 -0500 )edit
0

answered 2023-04-12 15:58:10 -0500

updated 2023-04-12 16:02:13 -0500

@NickC @jt1234 @Eric Ringold I just had someone ask me about this possibility for EnergyPlus to handle demand-side bypass, and hit the same severe error that Nick did using the Duct object type. But, I'm happy to share a workaround that at least simulates -- using a dummy zone on the demand side instead of the duct. Here was my process:

  1. Replace the Duct with a Zone object (call it dummy zone moving forward)
  2. Assign a dummy floor surface to the dummy zone (every zone needs at least one surface for EnergyPlus to run)
  3. Assign a VAV no-reheat terminal via the ZoneHVAC:ADU object to the dummy zone

The VAV no-reheat terminal allows the flow rate to vary, but applying EnergyPlus controls with the zones parallel to the dummy zone. In order to have the user outright set the desired bypass flow rate through the dummy zone, you would likely have to switch to a CAV no-reheat terminal so that you can use EMS and apply the Mass Flow Rate actuator for that specific terminal type.

You can compare my edited IDF that applied this process to the DOASDualDuctSchool.idf example file that I used as a starting point.

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I love a good workaround! Thanks for dredging this up. Curious if the AirLoopHVAC:UnitaryHeatCool:VAVChangeoverBypass would also work for your purpose?

ericringold's avatar ericringold  ( 2023-04-12 16:55:22 -0500 )edit

@Eric Ringold Nice find! It does seem that the Unitary VAV Changeover Bypass object would work for demand-side air bypass, looking at the last schematic specifically. There are some EP example files for this object type, but none of them utilize the Plenum or Mixer Inlet Node Name input field, so this would need some further testing to confirm.

Aaron Boranian's avatar Aaron Boranian  ( 2023-04-13 09:12:33 -0500 )edit

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Asked: 2017-05-04 18:56:44 -0500

Seen: 131 times

Last updated: Apr 12 '23