AirTerminal:SingleDuct:VAV:Reheat inputs for Constant and Fixed Minimum Air Flow Fraction/Rate do not get autosized for Method = Scheduled

[rraustad]

Issue overview

AirTerminal:SingleDuct:VAV:Reheat,
  N2 , \field Constant Minimum Air Flow Fraction
       \type real
       \autosizable
       \default autosize
       \note This field is used if the field Zone Minimum Air Flow Input Method is Constant
       \note If the field Zone Minimum Air Flow Input Method is Scheduled, then this field
       \note is optional; if a value is entered, then it is used for sizing normal-action reheat coils.
       \note If both this field and the following field are entered, the larger result is used.
       \note The values for autosizing are picked up from the Sizing:Zone input fields
       \note "Cooling Minimum Air Flow per Zone Floor Area", "Cooling Minimum Air Flow", and
       \note "Cooling Minimum Air Flow Fraction". If there is no sizing calculation a default of
       \note 0.000762 m3/s-m2 (0.15 cfm/ft2) is used.
  N3 , \field Fixed Minimum Air Flow Rate
       \type real
       \units m3/s
       \autosizable
       \default autosize

More than 1 issue here with these inputs for constant and fixed using the same variable DesignMinAirFrac when Zone Minimum Air Flow Input Method = Scheduled. I believe the fixed choice should use DesignFixedMinAir as used in the NoReheat version of this TU otherwise the constant choice input gets overwritten. A search for DesignMinAirFrac shows that this input is not autosized. A search for DesignFixedMinAir also shows that the Fixed input is never autosized. The variables ZoneMinAirFracDes and ZoneFixedMinAir are autosized but are not used when Method = Scheduled. Why is there an alternate variable describing these 2 input fields?

    CurrentModuleObject = "AirTerminal:SingleDuct:VAV:Reheat";

    state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).ZoneMinAirFracDes = Numbers(2);
    if (lNumericBlanks(2)) {
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).ConstantMinAirFracSetByUser = false;
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).DesignMinAirFrac = 0.0;
    } else {
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).ConstantMinAirFracSetByUser = true;
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).DesignMinAirFrac = Numbers(2);
    }

    state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).ZoneFixedMinAir = Numbers(3);
    if (lNumericBlanks(3)) {
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).FixedMinAirSetByUser = false;
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).DesignMinAirFrac = 0.0;
    } else {
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).FixedMinAirSetByUser = true;
        state.dataSingleDuct->sd_airterminal(state.dataSingleDuct->SysNumGSI).DesignMinAirFrac = Numbers(3);

This alternate variable for these 2 inputs fields are used when Method = Scheduled:

if (this->ZoneMinAirFracMethod == MinFlowFraction::Scheduled) {
    // need a value for sizing.
    if (this->ConstantMinAirFracSetByUser) {
        this->ZoneMinAirFracDes = this->DesignMinAirFrac;
        // if both inputs are defined, use the max
        if (this->FixedMinAirSetByUser) {
            this->ZoneMinAirFracDes = min(1.0, max(this->ZoneMinAirFracDes, SafeDivide(this->DesignFixedMinAir, this->MaxAirVolFlowRate)));
        }
        // if only fixed is defined, use the value
    } else if (this->FixedMinAirSetByUser) {
        this->ZoneMinAirFracDes = min(1.0, SafeDivide(this->DesignFixedMinAir, this->MaxAirVolFlowRate));
    } else {
        // use an average of min and max in schedule
        this->ZoneMinAirFracDes =
            (GetScheduleMinValue(state, this->ZoneMinAirFracSchPtr) + GetScheduleMaxValue(state, this->ZoneMinAirFracSchPtr)) / 2.0;
    }
}

Issue provided by Trane North America.

Details

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• Platform (Operating system, version)
• Version of EnergyPlus (if using an intermediate build, include SHA)
• Unmethours link or helpdesk ticket number

Checklist

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• Defect file added (5ZoneAirCooled-wConstantScheduledTU.txt, 5ZoneAirCooled-wFixedScheduledTU.txt)

• Ticket added to EnergyPlus Defect Complexity (Github Project)

• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)