Air leakage in parallel fan-powered terminal units #11038
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lymereJ
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@lymereJ @Myoldmopar it has been 31 days since this pull request was last updated. |
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@lymereJ @Myoldmopar it has been 34 days since this pull request was last updated. |
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@lymereJ @Myoldmopar it has been 30 days since this pull request was last updated. |
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@lymereJ @Myoldmopar it has been 28 days since this pull request was last updated. |
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@lymereJ Is this targeted for 25.2? |
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@mjwitte - Ideally, yes, but it's not quite ready. I'm hoping to be able to get back to it sometime next week. |
lymereJ
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The following plots show results generated using this branch for the new example file, for two cases: with and without leakage for the parallel PIU terminal serving "Space1-1". The terminal fan pulls air from "Space5-1", that is also the zone that is impacted by the leaks since they occur through the backdraft damper. Heating and dead-band operations:
Cooling operations:
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lymereJ
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Oct 11, 2025
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| // Get damper leakage inputs | ||
| if (cCurrentModuleObject == "AirTerminal:SingleDuct:ParallelPIU:Reheat") { | ||
| std::string damperLeakageFractionCurveName = | ||
| ip->getAlphaFieldValue(fields, objectSchemaProps, "backdraft_damper_leakage_fraction_curve_name"); | ||
| thisPIU.leakFracCurve = Curve::GetCurveIndex(state, damperLeakageFractionCurveName); | ||
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| if (!damperLeakageFractionCurveName.empty() && thisPIU.leakFracCurve == 0) { | ||
| ShowSevereError(state, | ||
| format("The air leakage fraction curve for the {} {} is missing. No air leakage will be modeled.", | ||
| cCurrentModuleObject, | ||
| thisPIU.Name)); | ||
| } else if (thisPIU.leakFracCurve > 0) { | ||
| // Find the secondary zone or plenum index | ||
| // The secondary air inlet node should either be a zone exhaust air node... | ||
| for (int zoneNum = 1; zoneNum <= state.dataGlobal->NumOfZones; ++zoneNum) { | ||
| for (int exhaustNum = 1; exhaustNum <= state.dataZoneEquip->ZoneEquipConfig(zoneNum).NumExhaustNodes; ++exhaustNum) { | ||
| if (thisPIU.SecAirInNode == state.dataZoneEquip->ZoneEquipConfig(zoneNum).ExhaustNode(exhaustNum)) { | ||
| state.dataHeatBal->Zone(zoneNum).isSourceForParallelPIU = true; | ||
| break; | ||
| } | ||
| } | ||
| } | ||
| // ... or an induced air node of a return plenum | ||
| for (int zoneNum = 1; zoneNum <= state.dataZonePlenum->NumZoneSupplyPlenums; ++zoneNum) { | ||
| for (int nodeNum = 1; nodeNum <= state.dataZonePlenum->ZoneRetPlenCond(zoneNum).NumInducedNodes; ++nodeNum) { | ||
| if (thisPIU.SecAirInNode == state.dataZonePlenum->ZoneRetPlenCond(zoneNum).InducedNode(nodeNum)) { | ||
| state.dataHeatBal->Zone(zoneNum).isSourceForParallelPIU = true; | ||
| break; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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New input validation for the leakage curve.
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| if (thisPIU.UnitType == "AirTerminal:SingleDuct:ParallelPIU:Reheat") { | ||
| SetupOutputVariable(state, | ||
| "Zone Air Terminal Backdraft Damper Leakage Mass Flow Rate", | ||
| Constant::Units::kg_s, | ||
| thisPIU.leakFlow, | ||
| OutputProcessor::TimeStepType::System, | ||
| OutputProcessor::StoreType::Average, | ||
| state.dataPowerInductionUnits->PIU(PIURpt).Name); | ||
| } |
There was a problem hiding this comment.
New input is only valid for parallel PIUs.
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| // PIU leakage calculations | ||
| if (thisPIU.leakFracCurve > 0 && state.dataHVACGlobal->TurnFansOn == false) { | ||
| // Determine leakage fraction as a function of the primary airflow fraction | ||
| const Real64 airflowFrac = thisPIU.PriAirMassFlow / thisPIU.MaxPriAirMassFlow; | ||
| thisPIU.leakFrac = min(1.0, Curve::CurveValue(state, thisPIU.leakFracCurve, airflowFrac)); | ||
| // Determine leakage rate that won't make it to the zone served by the terminal | ||
| thisPIU.leakFlow = thisPIU.leakFrac * thisPIU.PriAirMassFlow; | ||
| } |
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We're in dead-band operation here so we only determine the leakage based on the minimum primary air flow rate.
| // Determine leakage rate that won't make it to the zone served by the terminal | ||
| thisPIU.leakFlow = thisPIU.leakFrac * thisPIU.PriAirMassFlow; | ||
| // Increase the primary flow rate to meet the cooling load with leakage | ||
| thisPIU.PriAirMassFlow *= 1 / (1 - thisPIU.leakFrac); //(1 + thisPIU.leakFrac); |
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Same as above except that we're increasing the primary air flow rate to meet the load and when taking leaks into account.
| } | ||
| // Make sure that the primary airflow doesn't exceed the maximum when leakage is modeled | ||
| // When the primary airflow is limited to the maximum, the load won't likely be met | ||
| thisPIU.PriAirMassFlow = min(thisPIU.PriAirMassFlow, PriAirMassFlowMax); |
There was a problem hiding this comment.
Primary flow rate cannot be larger than the maximum value.
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| if (state.dataHeatBal->Zone(zoneNum).isSourceForParallelPIU) { | ||
| for (int iExhNode = 1; iExhNode <= state.dataZoneEquip->ZoneEquipConfig(zoneNum).NumExhaustNodes; ++iExhNode) { | ||
| int piuNum = | ||
| PoweredInductionUnits::getParallelPIUNumFromSecNodeNum(state, state.dataZoneEquip->ZoneEquipConfig(zoneNum).ExhaustNode(iExhNode)); | ||
| if (piuNum > 0) { | ||
| auto &thisPIU = state.dataPowerInductionUnits->PIU(piuNum); | ||
| MoistureMassFlowRate += (thisPIU.leakFlow * state.dataLoopNodes->Node(thisPIU.PriAirInNode).HumRat) / ZoneMult; | ||
| ZoneMassFlowRate += thisPIU.leakFlow / ZoneMult; | ||
| } | ||
| } | ||
| } | ||
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Impact of leaks on the zone conditions. Here, humidity, below temperature and sensible load.
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| state.dataDefineEquipment->AirDistUnit(ADUNum).MassFlowRateDnStrLk + | ||
| state.dataDefineEquipment->AirDistUnit(ADUNum) | ||
| .massFlowRateParallelPIULk; // Even though the PIU leakage flow rate doesn't necessarily go through the plenum, the same amount | ||
| // ends-up being returned |
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Account for PIU leaks separately from SDLM downstream leaks.
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| if ((airDistUnit.UpStreamLeak || airDistUnit.DownStreamLeak || airDistUnit.parallelPIUTerminalLeakFrac > 0.0) && | ||
| MassFlowRateMaxAvail > 0.0) { | ||
| airDistUnit.MassFlowRateTU = state.dataLoopNodes->Node(InNodeNum).MassFlowRate; | ||
| airDistUnit.MassFlowRateZSup = airDistUnit.MassFlowRateTU * (1.0 - airDistUnit.DownStreamLeakFrac); | ||
| airDistUnit.MassFlowRateZSup = | ||
| max(airDistUnit.MassFlowRateTU * (1.0 - airDistUnit.DownStreamLeakFrac - airDistUnit.parallelPIUTerminalLeakFrac), 0.0); | ||
| airDistUnit.MassFlowRateDnStrLk = airDistUnit.MassFlowRateTU * airDistUnit.DownStreamLeakFrac; | ||
| airDistUnit.massFlowRateParallelPIULk = airDistUnit.MassFlowRateTU * airDistUnit.parallelPIUTerminalLeakFrac; | ||
| airDistUnit.MassFlowRateSup = airDistUnit.MassFlowRateTU + airDistUnit.MassFlowRateUpStrLk; | ||
| state.dataLoopNodes->Node(InNodeNum).MassFlowRate = airDistUnit.MassFlowRateSup; | ||
| state.dataLoopNodes->Node(OutNodeNum).MassFlowRate = airDistUnit.MassFlowRateZSup; | ||
| state.dataLoopNodes->Node(OutNodeNum).MassFlowRateMaxAvail = | ||
| max(0.0, MassFlowRateMaxAvail - airDistUnit.MassFlowRateDnStrLk - airDistUnit.MassFlowRateUpStrLk); | ||
| max(0.0, | ||
| MassFlowRateMaxAvail - airDistUnit.MassFlowRateDnStrLk - airDistUnit.MassFlowRateUpStrLk - | ||
| airDistUnit.massFlowRateParallelPIULk); | ||
| state.dataLoopNodes->Node(OutNodeNum).MassFlowRateMinAvail = | ||
| max(0.0, MassFlowRateMinAvail - airDistUnit.MassFlowRateDnStrLk - airDistUnit.MassFlowRateUpStrLk); | ||
| max(0.0, | ||
| MassFlowRateMinAvail - airDistUnit.MassFlowRateDnStrLk - airDistUnit.MassFlowRateUpStrLk - | ||
| airDistUnit.massFlowRateParallelPIULk); |
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Leaks are "removed" from terminal outlet here.
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| // Nineth test - Cooling load TurnFansOn is false, yes primary flow - expecting secondary flow, leakage | ||
| state->dataLoopNodes->Node(PriNodeNum).MassFlowRate = state->dataPowerInductionUnits->PIU(SysNum).MaxPriAirMassFlow; | ||
| state->dataLoopNodes->Node(PriNodeNum).MassFlowRateMaxAvail = state->dataPowerInductionUnits->PIU(SysNum).MaxPriAirMassFlow; | ||
| state->dataLoopNodes->Node(PriNodeNum).MassFlowRateMinAvail = state->dataPowerInductionUnits->PIU(SysNum).MinPriAirMassFlow; | ||
| state->dataZoneEnergyDemand->ZoneSysEnergyDemand(1).RemainingOutputRequired = -2000.0; // Cooling load | ||
| state->dataZoneEnergyDemand->ZoneSysEnergyDemand(1).RemainingOutputReqToHeatSP = -2000.0; | ||
| state->dataZoneEnergyDemand->CurDeadBandOrSetback(1) = false; | ||
| state->dataHVACGlobal->TurnFansOn = false; | ||
| state->dataPowerInductionUnits->PIU(SysNum).leakFracCurve = Curve::GetCurveIndex(*state, "CONSTANT_LEAKAGE"); | ||
| PoweredInductionUnits::CalcParallelPIU(*state, SysNum, ZoneNum, ZoneNodeNum, FirstHVACIteration); | ||
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| Real64 SysOutputProvided = 0.0; | ||
| Real64 NonAirSysOutput = 0.0; | ||
| Real64 LatOutputProvided = 0.0; | ||
| int AirDistUnitNum = 1; | ||
| state->dataPowerInductionUnits->GetPIUInputFlag = false; | ||
| ZoneAirLoopEquipmentManager::SimZoneAirLoopEquipment(*state, | ||
| AirDistUnitNum, | ||
| SysOutputProvided, | ||
| NonAirSysOutput, | ||
| LatOutputProvided, | ||
| FirstHVACIteration, | ||
| state->dataPowerInductionUnits->PIU(SysNum).CtrlZoneNum); | ||
| EXPECT_TRUE(state->dataDefineEquipment->AirDistUnit(1).MassFlowRateTU > state->dataDefineEquipment->AirDistUnit(1).MassFlowRateZSup); | ||
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Piggy backing on existing test to test leak flow calculations.
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| // Check that parallel PIU leakage is accounted for | ||
| state->dataHeatBal->Zone(1).isSourceForParallelPIU = true; | ||
| state->dataPowerInductionUnits->GetPIUInputFlag = false; | ||
| state->dataPowerInductionUnits->NumPIUs = 1; | ||
| state->dataPowerInductionUnits->PIU.allocate(1); | ||
| state->dataPowerInductionUnits->PIU(1).SecAirInNode = 3; // exhaust node | ||
| state->dataPowerInductionUnits->PIU(1).PriAirInNode = 5; // primary air node | ||
| state->dataPowerInductionUnits->PIU(1).leakFlow = 0.1; | ||
| state->dataLoopNodes->Node(5).HumRat = 0.008; | ||
| state->dataLoopNodes->Node(5).Temp = 12.8; | ||
| thisZoneHB.calcZoneOrSpaceSums(*state, true, ZoneNum); | ||
| EXPECT_NEAR(402.67958, thisZoneHB.SumSysMCp, 0.0001); | ||
| EXPECT_NEAR(7328.768356, thisZoneHB.SumSysMCpT, 0.0001); |
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Same but for impacts of leaks to the zone conditions.
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Pull request overview
Add new inputs/outputs to model air leakage in parallel fan-powered terminal units.
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