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Fix #10663 - Fan runtime fraction < 1 when flow rate scaling using DesignSpecification:ZoneHVAC:Sizing #10673

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@jmarrec jmarrec commented Aug 21, 2024

Pull request overview

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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
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@jmarrec jmarrec added Defect Includes code to repair a defect in EnergyPlus NotIDDChange Code does not impact IDD (can be merged after IO freeze) labels Aug 21, 2024
@jmarrec jmarrec self-assigned this Aug 21, 2024
@@ -1011,7 +1011,7 @@ namespace WindowAC {
zoneEqSizing.SizingMethod(SizingMethod) = CapSizingMethod;
if (CapSizingMethod == CoolingDesignCapacity || CapSizingMethod == CapacityPerFloorArea ||
CapSizingMethod == FractionOfAutosizedCoolingCapacity) {
if (CapSizingMethod == HeatingDesignCapacity) {
if (CapSizingMethod == CoolingDesignCapacity) {
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This was an existing logic error that I noticed

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Good catch. Without example files or unit tests these are hard to find.

Comment on lines +1061 to +1063
// Make the Fan be sized by this
zoneEqSizing.CoolingAirFlow = true;
zoneEqSizing.CoolingAirVolFlow = windowAC.MaxAirVolFlow;
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This will size the Fan to match.

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} else if (this->zoneEqSizing(this->curZoneEqNum).CoolingAirFlow && !this->zoneEqSizing(this->curZoneEqNum).HeatingAirFlow) {
this->autoSizedValue = this->dataFracOfAutosizedCoolingAirflow * this->zoneEqSizing(this->curZoneEqNum).CoolingAirVolFlow;

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In SystemAirFlowSizing, if CoolingAirVolFlow = windowAC.MaxAirVolFlow (which should be already adjusted?) and dataFracOfAutosizedCoolingAirflow = the target fraction, then how does this get the right answer? I would think this would either be 1 * adjusted air flow or fraction * design air flow. This looks like it's fraction * adjusted air flow. Maybe windowAC.MaxAirVolFlow is the design air flow which gets multiplied by the fraction. In any event you are getting the right answer now.

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Apologies, I linked to the wrong bit in SystemAirFlowSizing. The correct bit is:

if (this->zoneEqSizing(this->curZoneEqNum).CoolingAirFlow && !this->zoneEqSizing(this->curZoneEqNum).HeatingAirFlow) {
this->autoSizedValue = this->zoneEqSizing(this->curZoneEqNum).CoolingAirVolFlow;

Process 2757796 stopped
* thread #1, name = 'energyplus', stop reason = step over
    frame #0: 0x00007ffff50d4370 libenergyplusapi.so.24.2.0`EnergyPlus::SystemAirFlowSizer::size(this=0x00007fffffff4d88, state=0x00007fffffffa980, _originalValue=-99999, errorsFound=0x00007fffffff529f) at SystemAirFlowSizing.cc:620:54
   617 	                    }
   618 	                } else {
   619 	                    if (this->zoneEqSizing(this->curZoneEqNum).CoolingAirFlow && !this->zoneEqSizing(this->curZoneEqNum).HeatingAirFlow) {
-> 620 	                        this->autoSizedValue = this->zoneEqSizing(this->curZoneEqNum).CoolingAirVolFlow;
   621 	                        if (this->finalZoneSizing(this->curZoneEqNum).CoolDDNum > 0 &&
   622 	                            this->finalZoneSizing(this->curZoneEqNum).CoolDDNum <= state.dataEnvrn->TotDesDays) {
   623 	                            DDNameFanPeak = state.dataWeather->DesDayInput(this->finalZoneSizing(this->curZoneEqNum).CoolDDNum).Title;
(lldb) p this->zoneEqSizing(this->curZoneEqNum).CoolingAirVolFlow
(Real64) 0.28246116346780509

Comment on lines +586 to +609
" WindowACSizing; !- Design Specification ZoneHVAC Sizing Object Name",

// NOTE: Only difference here is that I'm settting a DesignSpecification:ZoneHVAC:Sizing
" DesignSpecification:ZoneHVAC:Sizing,",
" WindowACSizing, !- Name",
" FractionOfAutosizedCoolingAirflow, !- Cooling Supply Air Flow Rate Method",
" , !- Cooling Supply Air Flow Rate {m3/s}",
" , !- Cooling Supply Air Flow Rate Per Floor Area {m3/s-m2}",
" 0.5, !- Cooling Fraction of Autosized Cooling Supply Air Flow Rate",
" , !- Cooling Supply Air Flow Rate Per Unit Cooling Capacity {m3/s-W}",
" FractionOfAutosizedCoolingAirflow, !- No Load Supply Air Flow Rate Method",
" , !- No Load Supply Air Flow Rate {m3/s}",
" , !- No Load Supply Air Flow Rate Per Floor Area {m3/s-m2}",
" 0.5, !- No Load Fraction of Cooling Supply Air Flow Rate",
" , !- No Load Fraction of Heating Supply Air Flow Rate",
" None, !- Heating Supply Air Flow Rate Method",
" , !- Heating Supply Air Flow Rate {m3/s}",
" , !- Heating Supply Air Flow Rate Per Floor Area {m3/s-m2}",
" , !- Heating Fraction of Heating Supply Air Flow Rate",
" , !- Heating Supply Air Flow Rate Per Unit Heating Capacity {m3/s-W}",
" FractionOfAutosizedCoolingCapacity, !- Cooling Design Capacity Method",
" , !- Cooling Design Capacity {W}",
" , !- Cooling Design Capacity Per Floor Area {W/m2}",
" 0.5; !- Fraction of Autosized Cooling Design Capacity",
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New unit test that uses a DesignSpecification:ZoneHVAC:Sizing

Comment on lines +948 to +976
double constexpr expected_full_airflow = 0.041484382187390034;
double constexpr scaler_cooling_saf = 0.5;
double constexpr scaler_cooling_cap = 0.5;
double constexpr expected_full_cap = 622.50474573886743;

auto const &windowAC = state->dataWindowAC->WindAC(compIndex);

ASSERT_GT(windowAC.FanIndex, 0);
auto const &fan = state->dataFans->fans(windowAC.FanIndex);

auto const &finalZoneSizing = state->dataSize->FinalZoneSizing(1);

EXPECT_NEAR(expected_full_airflow, finalZoneSizing.DesCoolVolFlow, 0.0001);

ASSERT_GT(windowAC.HVACSizingIndex, 0);
auto const &zoneHVACSizing = state->dataSize->ZoneHVACSizing(windowAC.HVACSizingIndex);

EXPECT_EQ(DataSizing::FractionOfAutosizedCoolingAirflow, zoneHVACSizing.CoolingSAFMethod);
EXPECT_EQ(scaler_cooling_saf, zoneHVACSizing.MaxCoolAirVolFlow);
EXPECT_EQ(DataSizing::FractionOfAutosizedCoolingCapacity, zoneHVACSizing.CoolingCapMethod);
EXPECT_EQ(scaler_cooling_cap, zoneHVACSizing.ScaledCoolingCapacity);

EXPECT_EQ(windowAC.DXCoilType_Num, HVAC::Coil_CoolingAirToAirVariableSpeed);
ASSERT_GT(windowAC.DXCoilIndex, 0);
auto const &varSpeedCoil = state->dataVariableSpeedCoils->VarSpeedCoil(windowAC.DXCoilIndex);

// check Sizing
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, windowAC.MaxAirVolFlow, 0.0001);
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, fan->maxAirFlowRate, 0.0001);
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Check that the Fan too is size at 0.5 of full flow

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From my previous comment about SystemAirFlowSizing, windowAC.MaxAirVolFlow is already adjusted. Now I'm confused.

EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, windowAC.MaxAirVolFlow, 0.0001);
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, fan->maxAirFlowRate, 0.0001);

EXPECT_NEAR(622.505, varSpeedCoil.RatedCapCoolTotal, 0.001);
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Note that the Coil:Cooling:DX:VariableSpeed is not affected.

  • I don't know if we would want that.
  • SizeVarSpeedCoil seem to not call the Autosizing modules. Instead, it uses the FinalZoneSizing's DesCoolVolFlow / DesCoolHeatFlow. cf
    CheckZoneSizing(state, format("COIL:{}{}", varSpeedCoil.CoolHeatType, CurrentObjSubfix), varSpeedCoil.Name);
    RatedAirVolFlowRateDes = max(state.dataSize->FinalZoneSizing(state.dataSize->CurZoneEqNum).DesCoolVolFlow,
    state.dataSize->FinalZoneSizing(state.dataSize->CurZoneEqNum).DesHeatVolFlow);

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The VS coil should be adjusted but it was never converted to use the sizing routines. That begs an open issue to adjust VS coil sizing when DesignSpecification:ZoneHVAC:Sizing is used.

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Filed at #10699

Comment on lines +1008 to +1011
// capacity sizing methods (HeatingDesignCapacity, CapacityPerFloorArea, FractionOfAutosizedCoolingCapacity, and
// FractionOfAutosizedHeatingCapacity )
int const CapSizingMethod = zoneHVACSizing.CoolingCapMethod;
zoneEqSizing.SizingMethod(SizingMethod) = CapSizingMethod;
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Note: I'm not sure if this is right... (this is pre-existing)

At this point in time, SizingMethod is either HVAC::CoolingAirflowSizing, or HVAC::CoolingCapacitySizing if the SAFMethod is FlowPerCoolingCapacity.

I think the intent here is to set the CoolingCapacitySizing method specifically, so it should be HVAC::CoolingCapacitySizing, right?

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The intent for FlowPerCoolingCapacity is:

  • calc design capacity using zone design air flow rate
  • set fraction that will adjust zone design air flow when air flow is sized (which will also adjust capacity when capacity is sized)

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just to be clear, you're saying this is currently correct right?

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Then the next time you call using HVAC::CoolingCapacitySizing the adjusted air flow rate would be used. It appears to me that the capacity sizer should be called here using SizingMethod = HVAC::CoolingCapacitySizing;. It looks like 1) state.dataSize->DataFlowUsedForSizing was not reset above to be an air flow rate (and DataFlowPerCoolingCapacity should be reset to 0), and 2) the sizing method should be explicitly set for capacity sizing (right now is looks to still be fraction of capacity).

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If you single step this a couple times you should see the capacity getting set using zone design air flow, the air flow being adjusted based on capacity, and the capacity being calculated again using the new air flow rate.

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jmarrec commented Aug 21, 2024

Note: these files are on DefectFiles support repo.

Taking the WindACAuto.idf and a modified Version WindACAutoScaled.idf that adds a DesignSpecification:ZoneHVAC:Sizing for the Zone1WindAC

image

I also added

  Output:Variable,Zone1WindACAirOutletNode,System Node Standard Density Volume Flow Rate,Detailed;
  Output:Variable,Zone1WindACFan,Fan Runtime Fraction,Detailed;

image

There is zero change for the WindACAuto.idf, as expected.

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jmarrec commented Aug 21, 2024

Comparing the component sizes

image

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This does look right except that 1 question with SystemAirFlowSizing.

Comment on lines +1008 to +1011
// capacity sizing methods (HeatingDesignCapacity, CapacityPerFloorArea, FractionOfAutosizedCoolingCapacity, and
// FractionOfAutosizedHeatingCapacity )
int const CapSizingMethod = zoneHVACSizing.CoolingCapMethod;
zoneEqSizing.SizingMethod(SizingMethod) = CapSizingMethod;
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The intent for FlowPerCoolingCapacity is:

  • calc design capacity using zone design air flow rate
  • set fraction that will adjust zone design air flow when air flow is sized (which will also adjust capacity when capacity is sized)

@@ -1011,7 +1011,7 @@ namespace WindowAC {
zoneEqSizing.SizingMethod(SizingMethod) = CapSizingMethod;
if (CapSizingMethod == CoolingDesignCapacity || CapSizingMethod == CapacityPerFloorArea ||
CapSizingMethod == FractionOfAutosizedCoolingCapacity) {
if (CapSizingMethod == HeatingDesignCapacity) {
if (CapSizingMethod == CoolingDesignCapacity) {
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Good catch. Without example files or unit tests these are hard to find.

Comment on lines +1061 to +1063
// Make the Fan be sized by this
zoneEqSizing.CoolingAirFlow = true;
zoneEqSizing.CoolingAirVolFlow = windowAC.MaxAirVolFlow;
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In SystemAirFlowSizing, if CoolingAirVolFlow = windowAC.MaxAirVolFlow (which should be already adjusted?) and dataFracOfAutosizedCoolingAirflow = the target fraction, then how does this get the right answer? I would think this would either be 1 * adjusted air flow or fraction * design air flow. This looks like it's fraction * adjusted air flow. Maybe windowAC.MaxAirVolFlow is the design air flow which gets multiplied by the fraction. In any event you are getting the right answer now.

Comment on lines +948 to +976
double constexpr expected_full_airflow = 0.041484382187390034;
double constexpr scaler_cooling_saf = 0.5;
double constexpr scaler_cooling_cap = 0.5;
double constexpr expected_full_cap = 622.50474573886743;

auto const &windowAC = state->dataWindowAC->WindAC(compIndex);

ASSERT_GT(windowAC.FanIndex, 0);
auto const &fan = state->dataFans->fans(windowAC.FanIndex);

auto const &finalZoneSizing = state->dataSize->FinalZoneSizing(1);

EXPECT_NEAR(expected_full_airflow, finalZoneSizing.DesCoolVolFlow, 0.0001);

ASSERT_GT(windowAC.HVACSizingIndex, 0);
auto const &zoneHVACSizing = state->dataSize->ZoneHVACSizing(windowAC.HVACSizingIndex);

EXPECT_EQ(DataSizing::FractionOfAutosizedCoolingAirflow, zoneHVACSizing.CoolingSAFMethod);
EXPECT_EQ(scaler_cooling_saf, zoneHVACSizing.MaxCoolAirVolFlow);
EXPECT_EQ(DataSizing::FractionOfAutosizedCoolingCapacity, zoneHVACSizing.CoolingCapMethod);
EXPECT_EQ(scaler_cooling_cap, zoneHVACSizing.ScaledCoolingCapacity);

EXPECT_EQ(windowAC.DXCoilType_Num, HVAC::Coil_CoolingAirToAirVariableSpeed);
ASSERT_GT(windowAC.DXCoilIndex, 0);
auto const &varSpeedCoil = state->dataVariableSpeedCoils->VarSpeedCoil(windowAC.DXCoilIndex);

// check Sizing
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, windowAC.MaxAirVolFlow, 0.0001);
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, fan->maxAirFlowRate, 0.0001);
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From my previous comment about SystemAirFlowSizing, windowAC.MaxAirVolFlow is already adjusted. Now I'm confused.

EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, windowAC.MaxAirVolFlow, 0.0001);
EXPECT_NEAR(expected_full_airflow * scaler_cooling_saf, fan->maxAirFlowRate, 0.0001);

EXPECT_NEAR(622.505, varSpeedCoil.RatedCapCoolTotal, 0.001);
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The VS coil should be adjusted but it was never converted to use the sizing routines. That begs an open issue to adjust VS coil sizing when DesignSpecification:ZoneHVAC:Sizing is used.

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Thanks for the review on this @rraustad, seems like this is very close, just maybe one remaining issue.

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This data shows that the single speed DX coil air flow was adjusted so it follows that the VS DX coil air flow should also be adjusted. Also in this data, why is the window AC scaled-ori and scaled-new values both equal to 0.02832 and the single speed DX coil air flow rate different?

}
bool errorsFound = false;
CoolingCapacitySizer sizerCoolingCapacity;
sizerCoolingCapacity.overrideSizingString(SizingString);
sizerCoolingCapacity.overrideSizingString("");
sizerCoolingCapacity.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
state.dataSize->DataCapacityUsedForSizing = sizerCoolingCapacity.size(state, TempSize, errorsFound);
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Yes, this does look correct. Call the cooling capacity sizer which uses zone design air flow.

sizerCoolingCapacity.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
state.dataSize->DataCapacityUsedForSizing = sizerCoolingCapacity.size(state, TempSize, errorsFound);
state.dataSize->DataFlowPerCoolingCapacity = state.dataSize->ZoneHVACSizing(zoneHVACIndex).MaxCoolAirVolFlow;
state.dataSize->DataFlowPerCoolingCapacity = zoneHVACSizing.MaxCoolAirVolFlow;
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Set the fraction of air flow here

sizingCoolingAirFlow.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
state.dataWindowAC->WindAC(WindACNum).MaxAirVolFlow = sizingCoolingAirFlow.size(state, TempSize, errorsFound);
windowAC.MaxAirVolFlow = sizingCoolingAirFlow.size(state, TempSize, errorsFound);
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And then size that new air flow rate here. You should also reset state.dataSize->DataFlowPerCoolingCapacity here to be a flow rate instead of a fraction.

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Final thoughts here @jmarrec ? Looks like @rraustad suggested at least one change to reset the DataFlowPerCoolingCapacity variable.

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@jmarrec these global fraction variables are hard to get right. It may be correct now, just check to make sure the final scaled values are as expected.

@Myoldmopar Myoldmopar added this to the EnergyPlus 25.1 IO Freeze milestone Sep 11, 2024
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jmarrec commented Sep 12, 2024

For some reason, probably lack of understanding, I'm severely confused about what's being asked here.

Code linting and unit test aside, I haven't touched the sections that are being commented. The actual changes are https://github.com/NREL/EnergyPlus/pull/10673/files/5dbc7b13c8597788540474a075a5eab678a3ce12..a5d32dea2e5a7ea6c68c38b6f073176a9cdc9ce1

I've been looking at other files to see if I could figure out what may be different here compared to other objects

} else if (SAFMethod == FlowPerCoolingCapacity) {
SizingMethod = HVAC::CoolingCapacitySizing;
TempSize = AutoSize;
PrintFlag = false;
state.dataSize->DataScalableSizingON = true;
state.dataSize->DataFlowUsedForSizing = state.dataSize->FinalZoneSizing(state.dataSize->CurZoneEqNum).DesCoolVolFlow;
if (zoneHVACSizing.CoolingCapMethod == FractionOfAutosizedCoolingCapacity) {
state.dataSize->DataFracOfAutosizedCoolingCapacity = zoneHVACSizing.ScaledCoolingCapacity;
}
bool errorsFound = false;
CoolingCapacitySizer sizerCoolingCapacity;
sizerCoolingCapacity.overrideSizingString("");
sizerCoolingCapacity.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
state.dataSize->DataCapacityUsedForSizing = sizerCoolingCapacity.size(state, TempSize, errorsFound);
state.dataSize->DataFlowPerCoolingCapacity = zoneHVACSizing.MaxCoolAirVolFlow;
PrintFlag = true;
TempSize = AutoSize;
errorsFound = false;
CoolingAirFlowSizer sizingCoolingAirFlow;
std::string stringOverride = "Maximum Supply Air Flow Rate [m3/s]";
if (state.dataGlobal->isEpJSON) {
stringOverride = "maximum_supply_air_flow_rate [m3/s]";
}
sizingCoolingAirFlow.overrideSizingString(stringOverride);
// sizingCoolingAirFlow.setHVACSizingIndexData(windowAC.HVACSizingIndex);
sizingCoolingAirFlow.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
windowAC.MaxAirVolFlow = sizingCoolingAirFlow.size(state, TempSize, errorsFound);

eg taking FanCoilUnits,

} else if (SAFMethod == DataSizing::FlowPerCoolingCapacity) {
SizingMethod = HVAC::CoolingCapacitySizing;
TempSize = DataSizing::AutoSize;
PrintFlag = false;
CoolingCapacitySizer sizerCoolingCapacity;
sizerCoolingCapacity.overrideSizingString(SizingString);
sizerCoolingCapacity.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
state.dataSize->DataAutosizedCoolingCapacity = sizerCoolingCapacity.size(state, TempSize, ErrorsFound);
if (state.dataSize->ZoneHVACSizing(zoneHVACIndex).CoolingCapMethod == DataSizing::FractionOfAutosizedCoolingCapacity) {
state.dataSize->DataFracOfAutosizedCoolingCapacity = state.dataSize->ZoneHVACSizing(zoneHVACIndex).ScaledCoolingCapacity;
}
state.dataSize->DataFlowPerCoolingCapacity = state.dataSize->ZoneHVACSizing(zoneHVACIndex).MaxCoolAirVolFlow;
PrintFlag = true;
TempSize = DataSizing::AutoSize;
state.dataSize->DataScalableSizingON = true;
CoolingAirFlowSizer sizingCoolingAirFlow;
sizingCoolingAirFlow.overrideSizingString(SizingString);
// sizingCoolingAirFlow.setHVACSizingIndexData(fanCoil.HVACSizingIndex);
sizingCoolingAirFlow.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
CoolingAirVolFlowDes = sizingCoolingAirFlow.size(state, TempSize, ErrorsFound);
}

Rewritting a bit the code to miminize diffs:

--- WindowAC.blob.cc	2024-09-12 12:17:47.094657049 +0200
+++ FanCoilUnits.blob.cc	2024-09-12 12:18:03.988792981 +0200
@@ -2,22 +2,21 @@
                     SizingMethod = HVAC::CoolingCapacitySizing;
                     TempSize = DataSizing::AutoSize;
                     PrintFlag = false;
-                    state.dataSize->DataScalableSizingON = true;
-                    state.dataSize->DataFlowUsedForSizing = state.dataSize->FinalZoneSizing(state.dataSize->CurZoneEqNum).DesCoolVolFlow;
-                    if (zoneHVACSizing.CoolingCapMethod == FractionOfAutosizedCoolingCapacity) {
-                        state.dataSize->DataFracOfAutosizedCoolingCapacity = zoneHVACSizing.ScaledCoolingCapacity;
-                    }
                     bool errorsFound = false;
                     CoolingCapacitySizer sizerCoolingCapacity;
                     sizerCoolingCapacity.overrideSizingString("");
                     sizerCoolingCapacity.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
-                    state.dataSize->DataCapacityUsedForSizing = sizerCoolingCapacity.size(state, TempSize, errorsFound);
+                    state.dataSize->DataAutosizedCoolingCapacity = sizerCoolingCapacity.size(state, TempSize, errorsFound);
+                    if (zoneHVACSizing.CoolingCapMethod == DataSizing::FractionOfAutosizedCoolingCapacity) {
+                        state.dataSize->DataFracOfAutosizedCoolingCapacity = zoneHVACSizing.ScaledCoolingCapacity;
+                    }
                     state.dataSize->DataFlowPerCoolingCapacity = zoneHVACSizing.MaxCoolAirVolFlow;
                     PrintFlag = true;
                     TempSize = DataSizing::AutoSize;
                     errorsFound = false;
+                    state.dataSize->DataScalableSizingON = true;
                     CoolingAirFlowSizer sizingCoolingAirFlow;
                     sizingCoolingAirFlow.overrideSizingString(SizingString);
                     sizingCoolingAirFlow.initializeWithinEP(state, CompType, CompName, PrintFlag, RoutineName);
-                    windowAC.MaxAirVolFlow = sizingCoolingAirFlow.size(state, TempSize, errorsFound);
+                    CoolingAirVolFlowDes = sizingCoolingAirFlow.size(state, TempSize, errorsFound);
                 }

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@jmarrec @Myoldmopar it has been 28 days since this pull request was last updated.

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@jmarrec @Myoldmopar it has been 28 days since this pull request was last updated.

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Fan runtime fraction < 1 when flow rate scaling using DesignSpecification:ZoneHVAC:Sizing
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