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Add exhaust fan for AirLoopHVAC:DedicatedOutdoorAirSystem #11395

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Merged
mitchute merged 8 commits into from
Jan 24, 2026
Merged

Add exhaust fan for AirLoopHVAC:DedicatedOutdoorAirSystem #11395

mitchute merged 8 commits into from
Jan 24, 2026
+5,792 −54

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@rraustad
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@rraustad rraustad commented Jan 14, 2026 •
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Pull request overview

Description of the purpose of this PR

The AirLoopHVAC:DedicatedOutdoorAirSystem did not allow an exhaust fan connected to the outlet of the DOAS system's AirLoopHVAC:Mixer object. These changes also check if the fan(s) are autosized or if not, use a maximum air volumetric flow rate that differs by more than 1% from the sum of the connected systems. If the flow rates differ a warning is issued but the fan flow rate is not changed.

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  • 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
  • If any defect files are updated to a more recent version, upload new versions here or on DevSupport
  • If IDD requires transition, transition source, rules, ExpandObjects, and IDFs must be updated, and add IDDChange label
  • If structural output changes, add to output rules file and add OutputChange label
  • If adding/removing any LaTeX docs or figures, update that document's CMakeLists file dependencies
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    • Update ..\scripts\RunEPlus.bat
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    • Update ...github\workflows\energyplus.py

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  • CI status: all green or justified
  • Check that performance is not impacted (CI Linux results include performance check)
  • Run Unit Test(s) locally
  • Check any new function arguments for performance impacts
  • Verify IDF naming conventions and styles, memos and notes and defaults
  • If new idf included, locally check the err file and other outputs

@rraustad rraustad added the Defect Includes code to repair a defect in EnergyPlus label Jan 14, 2026
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rraustad commented Jan 14, 2026

Defect file that includes a DOAS exhaust fan now operates correctly. Review of results show that the fan mass flow rate report variable does not correctly show flow while the node mass flow rate report show proper operation.

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mitchute commented Jan 15, 2026

Thanks @rraustad - looks good. I transitioned the test file to 26.1 and tested. That is added it here. What are your thoughts on adding it to the test suite? Based on the issue description, I would bet we don't have any tests that cover this use case either in the test files or the unit tests.

10280-SmallOffice_CentralDOAS_2Fans.idf.txt

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rraustad commented Jan 15, 2026

I can add this as an example file.

rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
errorsFound = true;
}
thisDOAS.m_CompPointerAirLoopMixer = AirLoopMixer::factory(state, thisDOAS.m_AirLoopMixerIndex, thisDOAS.AirLoopMixerName);

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@rraustad rraustad Jan 16, 2026

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The DOAS mixer code (old line 763) was moved here to read in mixer data and identify the mixer outlet node number. The following code can then check the fan inlet node to see if it matches a mixer outlet node. If so, then the fan is an exhaust fan. This is also the reason the unit test node numbers changed.

rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
thisDOAS.FanName = CompName;
thisDOAS.m_FanTypeNum = SimAirServingZones::CompType::Fan_System_Object;
thisDOAS.m_FanIndex = fanNum;
}
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The above variables are reserved for the DOAS supply fan. This new logic tries to isolate the first fan read in such that these variables are not overwritten by a second fan object.

rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
state.dataLoopNodes->NodeID(thisOutsideAirSys.InletNodeNum(CompNum)),
state.dataLoopNodes->NodeID(thisOutsideAirSys.OutletNodeNum(CompNum - 1))));
errorsFound = true;
if (isFan && thisOutsideAirSys.InletNodeNum(CompNum) == thisDOAS.m_CompPointerAirLoopMixer->OutletNodeNum) {
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And this new logic tests for a 2nd fan and updates new exhaust fan variables for use elsewhere. If there is no exhaust fan then the mismatched node warning is issued as before (else at 763).

rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
state.dataLoopNodes->Node(this->m_exhaustFanInletNodeNum).MassFlowRateMaxAvail = this->SumMassFlowRate;
state.dataLoopNodes->Node(this->m_exhaustFanOutletNodeNum).MassFlowRateMaxAvail = this->SumMassFlowRate;
state.dataLoopNodes->Node(this->m_exhaustFanOutletNodeNum).MassFlowRateMax = this->SumMassFlowRate;
}
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And then the rest of the changes are just accounting for a 2nd fan in the equipment list (i.e.,. this->m_exhaustFanUsed = true).

@rraustad rraustad added the NotIDDChange Code does not impact IDD (can be merged after IO freeze) label Jan 16, 2026
@rraustad rraustad added this to the EnergyPlus 26.1 IOFreeze milestone Jan 16, 2026
rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
if (this->m_FanIndex > 0 && (this->m_FanTypeNum == SimAirServingZones::CompType::Fan_System_Object ||
this->m_FanTypeNum == SimAirServingZones::CompType::Fan_ComponentModel)) {
Real64 supplyFanVolFlow = state.dataFans->fans(this->m_FanIndex)->maxAirFlowRate;
if (supplyFanVolFlow != DataSizing::AutoSize) {
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Check if fan is autosized before stomping on flow rate inputs. If not autosized then provide warning but don't set fan flow. If autosized then jump to else at 1032 and set air flow.

rraustad
rraustad commented Jan 16, 2026
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src/EnergyPlus/AirLoopHVACDOAS.cc
state.dataLoopNodes->Node(this->m_FanInletNodeNum).MassFlowRateMaxAvail = this->SizingMassFlow;
state.dataLoopNodes->Node(this->m_FanOutletNodeNum).MassFlowRateMaxAvail = this->SizingMassFlow;
state.dataLoopNodes->Node(this->m_FanOutletNodeNum).MassFlowRateMax = this->SizingMassFlow;
if (this->m_exhaustFanUsed) {
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And then use same sizing logic for the new exhaust fan.

mitchute
mitchute approved these changes Jan 16, 2026
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Thanks @rraustad. I think this is ready.

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mitchute commented Jan 24, 2026

Thanks @rraustad. Merging.

@mitchute mitchute merged commit 151da59 into develop Jan 24, 2026
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@mitchute mitchute deleted the 10280-DOAS-Return-Fan branch January 24, 2026 22:16
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Defect Includes code to repair a defect in EnergyPlus NotIDDChange Code does not impact IDD (can be merged after IO freeze)

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AirloopHVAC:DedicatedOutdoorAirSystem does not allow an exhaust fan

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