Fix 5ZoneNightVent3.idf, and test FanPerformance:NightVentilation by joseph-robertson · Pull Request #11595 · NatLabRockies/EnergyPlus

joseph-robertson · 2026-05-19T17:35:53Z

Pull request overview

Fixes AvailabilityManager:NightVentilation does not work #11475
Also create (re-introduce) 5ZoneNightVent4.idf test file with Fan:VariableVolume (instead of Fan:SystemModel) so we can actually test FanPerformance:NightVentilation.

Description of the purpose of this PR

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Reviewer

… and code.

…ct objects.

…htVentilation.

rraustad · 2026-05-19T23:16:46Z

Looks good.

joseph-robertson · 2026-05-20T15:59:06Z

The notes toward the beginning of the test file with AvailabilityManager:NightVentilation state that "Successful night ventilation modeling depends critically on getting the ventilation fan consumption right. In this case, we see no benefit with night ventilation compared to the base case (5ZoneNightVent1.idf)."

This would certainly explain the indifference described in #11475 and the unmethours link, but it's still not clear whether the statement is true because there is truly no benefit or whether there is an underlying bug. I think intuitively you'd expect at least some benefit given the scenario.

After some digging (i.e., adjusting night ventilation's schedules, limits, control zones, etc., and fan performance's total efficiency, pressure rise, etc.), it doesn't look like any combination actually affects the zone air temperature during the period when night ventilation is available. Maybe there are some key output variables to compare with 5ZoneNightVent2.idf's use of ZoneVentilation:DesignFlowRate which actually shows some night ventilation benefit? For example, "Air System Natural Ventilation Flow Rate" is nonzero for ZoneVentilation:DesignFlowRate but always zero for AvailabilityManager:NightVentilation.

rraustad · 2026-05-21T15:09:34Z

It looks to me as if the example file 5ZoneNightVent3 is working correctly (latest develop). If there is an issue with a defect file that could be handled separate from this change.

joseph-robertson · 2026-05-21T17:15:50Z

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


This is the fix to see nonzero airflow on the demand side of the loop during night ventilation.

See https://unmethours.com/question/103089/how-to-model-night-purge/ for more information.

This does reveal an issue with system control that was not noticed until now. This example file shows that the TU availability schedule affects night cycle operation, and system operation for that matter if the TU avail sch was more restrictive than the parent and fan avail schedules. In a parent object (e.g., UnitarySystem) the fan is controlled based on parent availability schedule and fan availability schedule. It appears that TU availability schedule also matters (and there are multiple TUs for air systems, at least 1 would need to be available). This was never noticed before maybe because TU avail schedules are typically always on or at least using the least restrictive schedule or maybe because night ventilation/cycle is used less often.

I'm throwing out a possible fix of TUs don't have avail schedules, they are always ON/available. Would that break anything? Would that restrict anything? Would that have less flexibility than is provided now?

joseph-robertson · 2026-05-21T17:17:15Z

-       \object-list FansCVandVAV
-       \object-list FansComponentModel


The docs say "At this time, it can be used with Fan:ConstantVolume, Fan:VariableVolume, Fan:ZoneExhaust, Fan:OnOff and Fan:SystemModel fans, but not with Fan:ComponentModel fans."

joseph-robertson · 2026-05-21T17:18:31Z

 !                                object. We ventilate the building in the early morning hours.
 !                                The runperiod is a summer week in Fresno. We assume a ventilation rate of 1/3 the
 !                                supply air design value and adjust the night ventilation fan performance
-!                                (FanPerformance:NightVentilation) object inputs accordingly.


This did not get updated starting with v8.7.0 when Fan:SystemModel was introduced and this test file was updated Fan:VariableVolume/FanPerformance:NightVentilation -> Fan:SystemModel.

joseph-robertson · 2026-05-21T17:19:43Z

 add_simulation_test(IDF_FILE 5ZoneNightVent1.idf EPW_FILE USA_CA_Fresno.Air.Terminal.723890_TMY3.epw)
 add_simulation_test(IDF_FILE 5ZoneNightVent2.idf EPW_FILE USA_CA_Fresno.Air.Terminal.723890_TMY3.epw)
 add_simulation_test(IDF_FILE 5ZoneNightVent3.idf EPW_FILE USA_CA_Fresno.Air.Terminal.723890_TMY3.epw)
+add_simulation_test(IDF_FILE 5ZoneNightVent4.idf EPW_FILE USA_CA_Fresno.Air.Terminal.723890_TMY3.epw)


Bring back the original night ventilation test file using FanPerformance:NightVentilation -- without it, this object is not tested anywhere.

github-actions · 2026-05-21T17:35:38Z

⚠️ Regressions detected on ubuntu-24.04 for commit `01efc9b`

Regression Summary

Audit: 1

github-actions · 2026-05-21T17:37:07Z

⚠️ Regressions detected on macos-14 for commit `01efc9b`

Regression Summary

Audit: 1

Copilot

Pull request overview

This PR addresses the reported night ventilation example problem in 5ZoneNightVent3.idf and reintroduces a companion example (5ZoneNightVent4.idf) to exercise FanPerformance:NightVentilation using a Fan:VariableVolume, along with corresponding IDD and documentation updates.

Changes:

Fix 5ZoneNightVent3.idf night ventilation behavior by ensuring VAV terminals remain available during night ventilation and by aligning the example narrative with Fan:SystemModel.
Add 5ZoneNightVent4.idf and register it as a simulation test to cover FanPerformance:NightVentilation with Fan:VariableVolume.
Update the IDD object-list restrictions for FanPerformance:NightVentilation, plus related Input Output Reference text.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
testfiles/CMakeLists.txt	Adds a simulation test entry for the new `5ZoneNightVent4.idf`.
testfiles/5ZoneNightVent4.idf	New example file using `Fan:VariableVolume` + `FanPerformance:NightVentilation` for night ventilation testing.
testfiles/5ZoneNightVent3.idf	Adjusts terminal availability and adds an AlwaysOn schedule; updates example narrative for `Fan:SystemModel`.
src/EnergyPlus/SystemAvailabilityManager.cc	Removes an unnecessary `using namespace DataAirLoop;` within night ventilation availability manager logic.
idd/Energy+.idd.in	Updates `FanPerformance:NightVentilation` allowed fan object-lists.
doc/input-output-reference/src/overview/group-system-availability-managers.tex	Minor wording tweak clarifying indoor/outdoor temperature difference description.
doc/input-output-reference/src/overview/group-fans.tex	Updates narrative/examples for `FanPerformance:NightVentilation` and cross-references.

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joseph-robertson · 2026-05-22T16:55:54Z

+!
+! Simulation Location/Run: FRESNO_CA_USA TMY2-93193, 2 design days, 1 run period,
+!                          Run Control executes the run period using the weather file
+!


Only flagged because this file is new. The others don't have this update. Seems unnecessary.

github-actions · 2026-05-21T20:57:22Z

⚠️ Regressions detected on macos-14 for commit `01efc9b`

Regression Summary

Audit: 1

github-actions · 2026-05-22T17:21:19Z

⚠️ Regressions detected on ubuntu-24.04 for commit `864adf5`

Regression Summary

Audit: 1

github-actions · 2026-05-22T17:24:43Z

⚠️ Regressions detected on macos-14 for commit `864adf5`

Regression Summary

Audit: 1

rraustad

This looks good to me. Anything else can be a follow up issue.

Joe Robertson added 5 commits May 19, 2026 10:29

Fix FanPerformance:NightVentilation fan object-list according to docs…

2361236

… and code.

Clean up FanPerformance:NightVentilation docs to align with code.

50557bd

Update night ventilation system model fan test file to describe corre…

17aeb8e

…ct objects.

Add night ventilation test file that actually uses FanPerformance:Nig…

b4a57b7

…htVentilation.

Update testfiles cmake for new night vent file.

9d38ab1

joseph-robertson self-assigned this May 19, 2026

joseph-robertson added Defect Includes code to repair a defect in EnergyPlus Documentation Related primarily on the LaTeX-based EnergyPlus documentation IDDChange Code changes impact the IDD file (cannot be merged after IO freeze) labels May 19, 2026

More docs updates for fans and avms.

a19c0be

Joe Robertson added 3 commits May 21, 2026 10:01

Update night vent test files with always on schedule for air terminals.

f8e0c15

Minor docs update.

a55462a

Merge branch 'develop' into avm-nightvent

ceb9831

joseph-robertson changed the title ~~Update and test FanPerformance:NightVentilation~~ Fix 5ZoneNightVent3.idf, and test FanPerformance:NightVentilation May 21, 2026

joseph-robertson commented May 21, 2026

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joseph-robertson marked this pull request as ready for review May 21, 2026 20:42

joseph-robertson requested a review from Copilot May 21, 2026 20:42

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joseph-robertson requested a review from mitchute May 22, 2026 15:12

Update docs, and idd/idf comments, based on review.

2d0f08b

rraustad approved these changes May 22, 2026

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github-actions Bot commented May 21, 2026

⚠️ Regressions detected on ubuntu-24.04 for commit 01efc9b

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github-actions Bot commented May 21, 2026

⚠️ Regressions detected on macos-14 for commit 01efc9b

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github-actions Bot commented May 21, 2026

⚠️ Regressions detected on macos-14 for commit 01efc9b

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github-actions Bot commented May 22, 2026

⚠️ Regressions detected on ubuntu-24.04 for commit 864adf5

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github-actions Bot commented May 22, 2026

⚠️ Regressions detected on macos-14 for commit 864adf5

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joseph-robertson commented May 19, 2026 •

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⚠️ Regressions detected on ubuntu-24.04 for commit `01efc9b`

⚠️ Regressions detected on macos-14 for commit `01efc9b`

⚠️ Regressions detected on macos-14 for commit `01efc9b`

⚠️ Regressions detected on ubuntu-24.04 for commit `864adf5`

⚠️ Regressions detected on macos-14 for commit `864adf5`