Inconsistent maximum flow rate for fans and terminals when sizing on ventilation needs

[lymereJ]

Issue overview

While working on #10368 I noticed that in the PlantLoopHeatPump_EIR_Large-Office-2-AWHP-DedHR-AuxBoiler-Pri-Sec-HW.idf test file that the maximum flow rate for the fan terminal is actually sized (based on ventilation needs) to be larger than the maximum terminal flow rate. For PIUs, this was previously not much of an issue because only constant volume fan operation were allowed.

Running the file in the debugger shows that the terminal is sized first and the fan second. Both of them are sized to the largest of the design heating/cooling zone air flow, but the terminal is further adjusted, or scaled, in UpdateSysSizing based on the zone OA to maximum terminal flow rate. The fan maximum flow rate is never adjusted accordingly. Fan sizing is done based on data in FinalZoneSizing whereas the adjustment to the terminal is done in data in TermUnitFinalZoneSizing.

EnergyPlus/src/EnergyPlus/SimAirServingZones.cc

Lines 6857 to 6862 in 7ee8539

	if ((SysHeatSizingRat != 1.0) && (finalSysSizing.loadSizingType == DataSizing::LoadSizing::Ventilation) &&
	(termUnitFinalZoneSizing.MinOA > 0.0)) {
	// size on ventilation load
	ZoneOARatio = termUnitFinalZoneSizing.MinOA / max(termUnitFinalZoneSizing.DesHeatVolFlow, termUnitFinalZoneSizing.MinOA);
	ZoneOARatio *= (1.0 + state.dataSize->TermUnitSizing(TermUnitSizingIndex).InducRat);
	termUnitFinalZoneSizing.scaleZoneHeating(ZoneOARatio);

Details

Some additional details for this issue (if relevant):

• Platform: Windows
• Version of EnergyPlus: 24.1

Checklist

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• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)