Fix ITE Standard Density Air Volume Flow Rate and Outdoor Air Details OA by Airloop calculation error, should divide by air density

[yujiex]

Pull request overview

• Fixes ITE Standard Density Air Volume Flow Rate calculation error #10567
• Fixes Outdoor Air Details report for Total Outdoor Air by Zone and AirLoop do not match #10112

In the code, the "ITE Standard Density Air Volume Flow Rate" is calculated as follows.

state.dataHeatBal->ZoneITEq(Loop).AirVolFlowStdDensity = AirMassFlowRate * state.dataEnvrn->StdRhoAir;

However, the volume flow rate should be the air mass flow rate divided by the air density, rather than multiplied by. This PR fixes this calculation error.

In the example file

before fixing, the calculated standard air pressure is around 0.8 kg/m3

after fixing, the calculated standard air pressure is around 1.2 kg/m3 (the correct value).

Regression diffs

ESO diff

1ZoneDataCenterCRAC_wApproachTemp
1ZoneDataCenterCRAC_wApproachTemp_ClassH1
1ZoneDataCenterCRAC_wPumpedDXCoolingCoil
2ZoneDataCenterHVAC_wEconomizer
2ZoneDataCenterHVAC_wEconomizer_ClassA1A2

The diffs are like this (the following is from 1ZoneDataCenterCRAC_wApproachTemp_ClassH1). These diffs are expected as we've changed the calculation of the ITE Standard Density Air Volume Flow Rate.

"Max absolute diff: 0.6383225713838598, field: DATA CENTER SERVERS:ITE Standard Density Air Volume Flow Rate [m3/s](Hourly), time:  12/21  01:00:00, relative: 0.07367292303016482"
"Max relative diff: 0.07367292303016501, field: DATA CENTER SERVERS:ITE Standard Density Air Volume Flow Rate [m3/s](Hourly), time:  07/21  24:00:00, absolute: 0.46079143420247703"

MTD, AUD diffs

1ZoneDataCenterCRAC_wApproachTemp
These are due to the following two added output:variables in the example file:
Output:Variable,,Zone ITE Standard Density Air Volume Flow Rate,Hourly;
Output:Variable,,Zone ITE Air Mass Flow Rate,Hourly;

Table big diffs

These appear in 329 files. See this csv file attached.
reg_diff_summary.csv
reg_diff_summary_label_table_diff_var.csv

• The diffs are mostly on "Mechanical Ventilation" and "Total Ventilaiton". These are expected.
• Some are on "Limits and Scheduled Limits", like in 5ZoneAirCooled.idf

The value for this table entry is calculated here in `avgFlowRate(iSys, MixedAir::OALimitFactor::Limits)`

 PreDefTableEntry(
                state, state.dataOutRptPredefined->pdchOaAvFctLimit, thisPrimaryAirSys.Name, avgFlowRate(iSys, MixedAir::OALimitFactor::Limits), 4);

The avgFlowRate definition is as follow.

auto avgFlowRate = [&state](int sysNum, MixedAir::OALimitFactor limitingFactorType) {
                int time = state.dataSysRpts->SysPreDefRep(sysNum).TimeAtOALimitOcc[static_cast<int>(limitingFactorType)];
                if (time > 0) {
                    return state.dataSysRpts->SysPreDefRep(sysNum).MechVentTotAtLimitOcc[static_cast<int>(limitingFactorType)] /
                           (time * Constant::SecInHour);
                } else {
                    return 0.0;
                }
            };

The MechVentToAtLimitOcc calculation involves mechVentFlow, which is impacted by this bug fix.

        // set time at OA limiting factors
        if (mechVentFlow > HVAC::SmallAirVolFlow) {
            int thisOAControlNum = state.dataAirLoop->AirLoopControlInfo(sysNum).OACtrlNum;
            if (thisOAControlNum > 0) {
                int limitFactorIndex = static_cast<int>(state.dataMixedAir->OAController(thisOAControlNum).OALimitingFactor);
                thisSysPreDefRep.TimeAtOALimit[limitFactorIndex] += TimeStepSys;
                if (thisSysVentRepVars.AnyZoneOccupied) {
                    thisSysPreDefRep.TimeAtOALimitOcc[limitFactorIndex] += TimeStepSys;
                    thisSysPreDefRep.MechVentTotAtLimitOcc[limitFactorIndex] += mechVentFlow * TimeStepSysSec;
                }
            }
        }

• Some have diffs in Time Below Voz-sum-dyn, Time At Voz-sum-dyn, or Time Above Voz-sum-dyn. One example is the

The following shows the relevant code computing the table entry "Time At Voz-sum-dyn [hr]". The totMechNatVentVolFlowStdRho variable is computed using mechVentFlow, thus this regression diff is expected as well.

 s->pdchOaTaAlTmAt = newPreDefColumn(state, s->pdstOAtotAirByLoop, "Time At Voz-sum-dyn [hr]");
...
 PreDefTableEntry(state, state.dataOutRptPredefined->pdchOaTaAlTmAt, thisPrimaryAirSys.Name, thisSysPreDefRep.TimeAtVozDynTotal);
...
 Real64 totMechNatVentVolFlowStdRho = mechVentFlow + thisSysVentRepVars.NatVentFlow;
...
 } else if (totMechNatVentVolFlowStdRho > HVAC::SmallAirVolFlow) {
            thisSysVentRepVars.TimeAtVozDyn = TimeStepSys;
            thisSysPreDefRep.TimeAtVozDynTotal += TimeStepSys;
}

• Some have diffs in "Exhaust Flow". One example is the "5ZoneAirCooled_ZoneAirMassFlowBalance.idf"

The following are relevant code computing this table entry. As is explained above, the avgFlowRate calculation involves mechVentFlow, which is impacted by this bug fix. This regression diff is expected.

        s->pdchOaAvFctExhaust = newPreDefColumn(state, s->pdstOAavgFactorsDurOcc, "Exhaust Flow [m3/s]");              // todo
        PreDefTableEntry(state,
                          state.dataOutRptPredefined->pdchOaAvFctExhaust,
                          thisPrimaryAirSys.Name,
                          avgFlowRate(iSys, MixedAir::OALimitFactor::Exhaust),
                          4);

• Some diffs are in "Mixed Air Flow". One example is the "5ZoneCoolingPanelBaseboard.idf"

The following are relevant code computing this table entry. As is explained above, the avgFlowRate calculation involves mechVentFlow, which is impacted by this bug fix. This regression diff is expected.

        s->pdchOaAvFctMixedLimit = newPreDefColumn(state, s->pdstOAavgFactorsDurOcc, "Mixed Air Flow [m3/s]");         // todo
        PreDefTableEntry(state,
                          state.dataOutRptPredefined->pdchOaAvFctMixedLimit,
                          thisPrimaryAirSys.Name,
                          avgFlowRate(iSys, MixedAir::OALimitFactor::MixedAir),
                          4);

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[mjwitte]

@yujiex Have you searched the code for * state.dataEnvrn->StdRhoAir to see if there are any other similar mistakes?

[mjwitte]

But that will have lots of hits for converting volume to mass flow.

[yujiex]

@yujiex Have you searched the code for * state.dataEnvrn->StdRhoAir to see if there are any other similar mistakes?

Let me check

[yujiex]

But that will have lots of hits for converting volume to mass flow.

It seems most places convert volume to mass flow rate, not the other way, so "*" is correct in those places.

[yujiex]

I looked at ones using "* state.dataEnvrn->StdRhoAir".
The following are all volume flow rate multiplied by density (correct) (note DataAirFlowUsedForSizing, MinOA, SysOAuc are volume flow rate)

The following one might be wrong, as OAFlow is mass flow rate and MechVentFlow is "air loop mechanical vent total volume OA at standard density {m3/s}"

[mjwitte]

The following one might be wrong, as OAFlow is mass flow rate and MechVentFlow is "air loop mechanical vent total volume OA at standard density {m3/s}"

Yes, that one is wrong. It is being fixed in #10518

[mjwitte]

But I could close that and let the fix go in here. One less PR to review.

[yujiex]

But I could close that and let the fix go in here. One less PR to review.

that works =)

[Myoldmopar]

Lots of diffs here, but an obvious fix. I'm inclined to drop this fix right in. @mjwitte any hesitation at this point?

[mjwitte]

Lots of diffs here, but an obvious fix. I'm inclined to drop this fix right in. @mjwitte any hesitation at this point?

None here. Full speed ahead, cap'n!

[yujiex]

Thanks @Myoldmopar and @mjwitte =)