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How to model Night Purge

asked 2026-02-24 03:28:16 -0500

Keigo's avatar

Has anyone modelled night purge (night ventilation) in EnergyPlus using AvailabilityManager:NightVentilation?

I ran two ExampleFiles: 5ZoneNightVent1.idf and 5ZoneNightVent3.idf (V25-1-0). Night purge is not modelled in 5ZoneNightVent1.idf and modelled in 5ZoneNightVent3.idf.

I got exactly the same annual cooling end use from the two files, which suggests that night purge in 5ZoneNightVent3.idf is not working.

The simulation results show that the fan operates at night when the condition allows, but the outdoor air is not reaching each zone. Only 4 nodes in OutdoorAir:Mixer have 0.5m3/s airflow during night purge. Other nodes have no airflow. This may be a bug.

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For what it's worth, I ran all 3 models:

  1. 5ZoneNightVent1.idf
  2. 5ZoneNightVent2.idf
  3. 5ZoneNightVent3.idf

... for an entire year (not a week), and in a colder climate zone (than Fresno, California):

  • fan energy use varied between all 3 models, from 2 to 3%
  • slight differences in cooling (< 1%) between 1 vs 2, and 2 vs 3
  • as you observed, no differences in cooling between 1 vs 3

Have not taken a deeper dive as to why?

Denis Bourgeois's avatar Denis Bourgeois  ( 2026-02-24 06:50:57 -0500 )edit

5ZoneNightVent2.idf models night purge with ZoneVentilation:DesignFlowRate. That's another option. I'm wondering if AvailabilityManager:NightVentilation will work. If not, ZoneVentilation:DesignFlowRate is only per zone, but I think it is possible to mimic the existing fan objects.

Keigo's avatar Keigo  ( 2026-02-24 07:33:03 -0500 )edit
1

Reported. https://github.com/NatLabRockies/EnergyPlus/issues/11475

Keigo's avatar Keigo  ( 2026-03-18 00:53:52 -0500 )edit
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answered 2026-05-21 11:05:51 -0500

rraustad's avatar

updated 2026-05-21 11:33:55 -0500

@Keigo, when I run 5ZoneNightVent3 in the latest V26.2 I see OA and system air flow. I didn't check all nodes in the air loop and zones but it does appear to me that the system activates for Night Ventilation.

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UPDATE: I added zone nodes to the investigation. Sure enough the zone side of the system has 0 flow during NightVentilation. This is because the TU is using the fan schedule when it should be Always ON.

   AirTerminal:SingleDuct:VAV:Reheat,      SPACE1-1 VAV Reheat,     !- Name      FanAvailSched,           !- Availability Schedule Name

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Sure enough the zone side of the system has 0 flow during NightVentilation. This is because the TU is using the fan schedule when it should be Always ON.

Sould Availability Schedule Name of AirTerminal:SingleDuct:VAV:Reheat be left blank? Or will AvailabilityManager:NightVentilation in EnergyPlus 26-2-0 extend not only the fan availability schedule but also the TU availability schedule?

Keigo's avatar Keigo  ( 2026-05-26 19:06:42 -0500 )edit
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The NIghtVentilation model did not anticipate needing to check the TU availability schedule. Using a blank or always 1 (on) schedule should fix this issue.

rraustad's avatar rraustad  ( 2026-05-27 20:18:00 -0500 )edit
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Asked: 2026-02-24 03:28:16 -0500

Seen: 348 times

Last updated: May 27

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