Outdoor Air Schedule Name in DesignSpecification:OutdoorAir does not work

[keigo-nomura]

Issue overview

As per the title. Outdoor Air Schedule Name in DesignSpecification:OutdoorAir does not change outdoor air flow rate. Please refer to the Unmethours link below for more details on the issue.

Details

Some additional details for this issue (if relevant):

• Version of EnergyPlus: V23-1-0
• Unmethours link: Outdoor Air Schedule Name in DesignSpecification:OutdoorAir does not work

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• Defect file added (list location of defect file here)
• 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)

[jmarrec]

Taking the 5ZoneFanCoilDOASCool_rev.idf example you shared:

AirTerminal:SingleDuct:VAV:NoReheat,
    SPACE1-1 DOAS Air Terminal,  !- Name
    ,                        !- Availability Schedule Name
    SPACE1-1 DOAS Supply Inlet,  !- Air Outlet Node Name
    SPACE1-1 Zone Equip Inlet,  !- Air Inlet Node Name
    autosize,                !- Maximum Air Flow Rate {m3/s}
-   Constant,                !- Zone Minimum Air Flow Input Method
-   1.0,                     !- Constant Minimum Air Flow Fraction
    ,                        !- Fixed Minimum Air Flow Rate {m3/s}
    ,                        !- Minimum Air Flow Fraction Schedule Name
+   SZ DSOA SPACE1-1;        !- Design Specification Outdoor Air Object Name

EnergyPlus/src/EnergyPlus/SingleDuct.cc

Lines 3953 to 3962 in 07b51a2

	// calculate supply air flow rate based on user specified OA requirement
	this->CalcOAMassFlow(state, MassFlowBasedOnOA, AirLoopOAFrac);
	MassFlow = max(MassFlow, MassFlowBasedOnOA);
	// Check to see if the flow is < the Min or > the Max air Fraction to the zone; then set to min or max
	if (MassFlow <= this->sd_airterminalInlet.AirMassFlowRateMinAvail) {
	MassFlow = this->sd_airterminalInlet.AirMassFlowRateMinAvail;
	} else if (MassFlow >= this->sd_airterminalInlet.AirMassFlowRateMaxAvail) {
	MassFlow = this->sd_airterminalInlet.AirMassFlowRateMaxAvail;
	}

CalcOAMassFlow correctly calculates it to be zero because of the OutdoorAirAvailSched. But:

(lldb) p MassFlow
(Real64) $10 = 0.12210386490935213
(lldb) p MassFlowBasedOnOA
(Real64) $11 = 0
(lldb) p this->sd_airterminalInlet.AirMassFlowRateMinAvail
(Real64) $12 = 0.12210386490935213
(lldb) p this->sd_airterminalInlet.AirMassFlowRateMaxAvail
(Real64) $13 = 0.12210386490935213

So it's always going to be 0.12 anyways because the Minimum Air Flow Fraction is constant at 1.0.

You'll see a change in results (but still not what you probably expect) if you set this to 0.0. If you want to model this properly, you also probably want to add a Controller:MechanicalVentilation object on the AirLoopHVAC's Controller:OutdoorAir, and list the zones + DSOAs onto that Controller:MV.

[mjwitte]

This is working as designed, but could probably use some documentation updates to help clarify (I/O Reference and IDD notes).
See answer here for more details.