Fix heating and cooling runtime fraction for `AirLoopHVAC:UnitarySystem` for airflow network simulations by lymereJ · Pull Request #11491 · NatLabRockies/EnergyPlus

lymereJ · 2026-03-31T22:23:37Z

Pull request overview

Fixes Incorrect heating energy use for AirLoopHVAC:UnitarySystem in AFN simulation with distribution losses #11490

Pull Request Author

Title of PR should be user-synopsis style (clearly understandable in a standalone changelog context)
Label the PR with at least one of: Defect, Refactoring, NewFeature, Performance, and/or DoNoPublish
Pull requests that impact EnergyPlus code must also include unit tests to cover enhancement or defect repair
Author should provide a "walkthrough" of relevant code changes using a GitHub code review comment process
If any diffs are expected, author must demonstrate they are justified using plots and descriptions
If changes fix a defect, the fix should be demonstrated in plots and descriptions

Reviewer

lymereJ · 2026-03-31T22:28:22Z

Here's a comparison of the duct conduction heat gains for the defect file with the "reference" file with this branch:

Also, as expected their energy use is virtually the same:

OPT4 (AirLoopHVAC:UnitarySystem):

OPT3 (AirLoopHVAC:UnitaryHeatCool):

lymereJ

Code walk-through:

lymereJ · 2026-03-31T22:29:58Z

src/EnergyPlus/UnitarySystem.cc

        // Report the current output
        this->reportUnitarySystem(state, AirLoopNum);

+        // Get the actual maximum RTF for AFN simulations


Similar changes as for #11367. We save the RTFs at the system level instead of at the coil level and make the determination here, that way we can also include the supplemental heating coil.

lymereJ · 2026-03-31T22:30:52Z

src/EnergyPlus/UnitarySystem.cc

        int CompIndex = this->m_HeatingCoilIndex;
        HVAC::FanOp fanOp = this->m_FanOpMode;
        Real64 DesOutTemp = this->m_DesiredOutletTemp;
-


These were only applied when the system is controller to a setpoint. The propose changes apply to both load-based and setpoint control.

lymereJ · 2026-03-31T22:31:23Z

tst/EnergyPlus/unit/UnitarySystem.unit.cc

+                     latOut);
+
+    // Check that the runtime fraction is less than one so the impact of cycling fan is correctly accounted for in the AFN
+    EXPECT_TRUE(state->dataAirLoop->AirLoopAFNInfo(1).AFNLoopHeatingCoilMaxRTF < 1);


New unit test to make sure that the correct RTF is retrieved. This verification fails on develop.

github-actions · 2026-03-31T22:38:07Z

⚠️ Regressions detected on ubuntu-24.04 for commit `7c78951`

Regression Summary

ESO Small Diffs: 703
Table Small Diffs: 391
MTR Small Diffs: 523
Table String Diffs: 186
EIO: 396
JSON Small Diffs: 2
ZSZ Small Diffs: 72
Table Big Diffs: 36
ERR: 14
MTR Big Diffs: 2
EDD: 4
ESO Big Diffs: 10
SSZ Small Diffs: 13
JSON Big Diffs: 2

rraustad · 2026-04-01T14:56:53Z

src/EnergyPlus/UnitarySystem.cc


+        // Get the actual maximum RTF for AFN simulations
+        if (state.afn->distribution_simulated && this->m_sysType != SysType::PackagedAC && this->m_sysType != SysType::PackagedHP &&
+            this->m_sysType != SysType::PackagedWSHP && AirLoopNum > 0) {


I think there may be a problem with these conditionals. The first is that we should move away from checking for the "Packaged" sysType because it was added to reduce diffs. These special considerations should be removed slowly and will cause little diffs so should probably be done 1 at a time. What is important here is that this is a system level object. Not zone equipment, OA sys equipment, or in a ZoneHVAC:OutdoorAirUnit object. The second is that AirLoopNum > 0 will also be true (I think) for a UnitarySystem in the OutdoorAir system.

This conditional would be the same as:

if (state.afn->distribution_simulated && !this->IsZoneEquipment && AirLoopNum > 0) {

except the snag that this system could be called from MixedAir and be part of an outdoor air system. You could probably use this to capture a system object (air loop equipment):

if (state.afn->distribution_simulated && AirLoopNum > 0 && state.dataSize->CurOASysNum == 0) {

I am not positive that AFN would not include OA systems here but if so then CurOASysNum==0 would not be needed (I think it's needed).

I see, thanks. I was following the existing pattern. Should these mods be done as a follow up PR, or should I include them here?

Just include them here. This is a small change that also gets rid of some "Packaged" sysType checks.

I made the changes.

rraustad · 2026-04-01T15:15:26Z

src/EnergyPlus/UnitarySystem.cc

+        if (state.afn->distribution_simulated && this->m_sysType != SysType::PackagedAC && this->m_sysType != SysType::PackagedHP &&
+            this->m_sysType != SysType::PackagedWSHP && AirLoopNum > 0) {
+            refAFNLoopHeatingCoilMaxRTF = state.dataAirLoop->AirLoopAFNInfo(AirLoopNum).AFNLoopHeatingCoilMaxRTF;
+            refAFNLoopCoolingCoilMaxRTF = state.dataAirLoop->AirLoopAFNInfo(AirLoopNum).AFNLoopDXCoilRTF;


Can't you just move these last 2 lines down inside of the block below?

I don't think so because I think this needs to happen before controlUnitarySystemtoSP or controlUnitarySystemtoLoad are called.

I see. Because these same AFN variables are set in the child. In this parent there can be 2 heating coils so the larger RTF should be used and calling the control functions will set AFNLoopHeatingCoilMaxRTF to the RTF of the last coil called.

lymereJ added 3 commits March 31, 2026 12:53

Set the AFN coil runtime fraction in simulate().

40a94b9

Merge branch 'develop' into fix_unitary_system_afn_runtime_fracs

92174e5

Add unit test

991df4f

lymereJ added the Defect Includes code to repair a defect in EnergyPlus label Mar 31, 2026

lymereJ commented Mar 31, 2026

View reviewed changes

lymereJ added the AirflowNetwork Related primarily on airflow-network portions of the codebase label Apr 1, 2026

lymereJ modified the milestone: EnergyPlus 26.2 Bug Fix Freeze Apr 1, 2026

rraustad reviewed Apr 1, 2026

View reviewed changes

Address review comments.

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github-actions bot commented Mar 31, 2026

⚠️ Regressions detected on ubuntu-24.04 for commit 7c78951

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rraustad Apr 1, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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lymereJ commented Mar 31, 2026 •

edited

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⚠️ Regressions detected on ubuntu-24.04 for commit `7c78951`

rraustad Apr 1, 2026 •

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