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Fix ThirdOrderBackwardDifference Zone Air Heat Balance Storage Reporting #11871

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Merged
mitchute merged 1 commit into from
Oct 21, 2026
+24 −7
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Fix ThirdOrderBackwardDifference Zone Air Heat Balance Storage Reporting #11871

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11 changes: 4 additions & 7 deletions src/EnergyPlus/ZoneTempPredictorCorrector.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -5681,17 +5681,14 @@ void CalcZoneComponentLoadSums(EnergyPlusData &state,
}
}
}
// now calculate air energy storage source term.
// capacitance is volume * density * heat capacity
Real64 CpAir = Psychrometrics::PsyCpAirFnW(thisHB->airHumRat);
Real64 RhoAir = Psychrometrics::PsyRhoAirFnPbTdbW(state, state.dataEnvrn->OutBaroPress, thisHB->MAT, thisHB->airHumRat);

// Calculate the air energy storage term using the same capacitance and time integration method as the zone air temperature solver.
switch (state.dataHeatBal->ZoneAirSolutionAlgo) {
case DataHeatBalance::SolutionAlgo::ThirdOrder: {
thisAirRpt.CzdTdt = RhoAir * CpAir * thisZone.Volume * thisZone.ZoneVolCapMultpSens * (thisHB->MAT - thisHB->ZTM[0]) / TimeStepSysSec;
// Exact solution
thisAirRpt.CzdTdt =
thisHB->AirPowerCap * ((11.0 / 6.0) * thisHB->MAT - 3.0 * thisHB->ZTM[0] + (3.0 / 2.0) * thisHB->ZTM[1] - (1.0 / 3.0) * thisHB->ZTM[2]);
} break;
case DataHeatBalance::SolutionAlgo::AnalyticalSolution: {
// Exact solution
thisAirRpt.CzdTdt = thisHB->TempIndCoef - thisHB->TempDepCoef * thisHB->MAT;
} break;
case DataHeatBalance::SolutionAlgo::EulerMethod: {
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20 changes: 20 additions & 0 deletions tst/EnergyPlus/unit/ZoneTempPredictorCorrector.unit.cc
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Expand Up @@ -1117,6 +1117,26 @@ TEST_F(EnergyPlusFixture, ZoneTempPredictorCorrector_calcZoneOrSpaceSums_SurfCon
EXPECT_NEAR(7328.768356, thisZoneHB.SumSysMCpT, 0.0001);
}

TEST_F(EnergyPlusFixture, ZoneTempPredictorCorrector_ThirdOrderComponentLoadStorageTest)
{
state->init_state(*state);

state->dataHeatBal->Zone.allocate(1);
state->dataHeatBalFanSys->SumConvHTRadSys.allocate(1);
state->dataHeatBalFanSys->SumConvPool.allocate(1);

ZoneTempPredictorCorrector::ZoneHeatBalanceData zoneHB;
zoneHB.AirPowerCap = 100.0;
zoneHB.MAT = 23.0;
zoneHB.ZTM = {20.0, 19.0, 18.0, 0.0};

state->dataHeatBal->ZoneAirSolutionAlgo = DataHeatBalance::SolutionAlgo::ThirdOrder;
DataHeatBalance::AirReportVars airReport;
CalcZoneComponentLoadSums(*state, 1, &zoneHB, airReport);

EXPECT_NEAR(1400.0 / 3.0, airReport.CzdTdt, 1.0e-10);
}

TEST_F(EnergyPlusFixture, ZoneTempPredictorCorrector_EMSOverrideSetpointTest)
{
// AUTHOR: L. Gu, FSEC
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