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

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

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9d0bef8
Improve an existing unit test (I plan to use a variation of this)
jmarrec Aug 20, 2024
dddaa5a
New unit test for #10663
jmarrec Aug 20, 2024
52ffb00
Take a reference directly
jmarrec Aug 19, 2024
5dbc7b1
Revamp the routine to take more references to shorten the code, scope…
jmarrec Aug 20, 2024
f472e96
Fix existing logic error related to Cooling Capacity sizing
jmarrec Aug 19, 2024
a5d32de
Set CoolingAirFlow flag in WindowAC so fan is sized by the WindowAC
jmarrec Aug 20, 2024
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5 changes: 4 additions & 1 deletion src/EnergyPlus/WindowAC.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -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.

if (zoneHVACSizing.ScaledCoolingCapacity > 0.0) {
zoneEqSizing.CoolingCapacity = true;
zoneEqSizing.DesCoolingLoad = zoneHVACSizing.ScaledCoolingCapacity;
Expand Down Expand Up @@ -1058,6 +1058,9 @@ namespace WindowAC {

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

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EnergyPlus/src/EnergyPlus/Autosizing/SystemAirFlowSizing.cc

Lines 237 to 238 in f274ccb

} 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:

EnergyPlus/src/EnergyPlus/Autosizing/SystemAirFlowSizing.cc

Lines 619 to 620 in 54f875d

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

}

state.dataSize->DataScalableCapSizingON = false;
Expand Down
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