Update AirTerminal:SingleDuct:Mixer to report primary air node condition when air flow = 0 (when ATMixer is off)

[rraustad]

Pull request overview

• Fixes AirTerminal:SingleDuct:Mixer reports odd mixed air condition during off cycle #11021
• This correction sets the mixed air condition of the ATMixer to be equal to the primary inlet node when air flow rate = 0. Since this occurs during the off condition it doesn't really matter what condition is reported so it was chosen to report the mixed air condition the same as the primary inlet node. This is the same methodology used when calculating CO2 or contaminants.

    if (state.dataContaminantBalance->Contaminant.CO2Simulation) {
        if (state.dataSingleDuct->SysATMixer(SysNum).MixedAirMassFlowRate <= HVAC::VerySmallMassFlow) {
            state.dataLoopNodes->Node(MixedAirOutNode).CO2 = state.dataLoopNodes->Node(PriInNode).CO2;
        } else {
            state.dataLoopNodes->Node(MixedAirOutNode).CO2 =
                (state.dataLoopNodes->Node(SecInNode).MassFlowRate * state.dataLoopNodes->Node(SecInNode).CO2 +
                 state.dataLoopNodes->Node(PriInNode).MassFlowRate * state.dataLoopNodes->Node(PriInNode).CO2) /
                state.dataLoopNodes->Node(MixedAirOutNode).MassFlowRate;
        }
    }

Description of the purpose of this PR

This change reports the off condition of the ATMixer to be equal to the primary inlet node condition to replicate other node properties.

Pull Request Author

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[rraustad]

The same figure as shown in the issue description is shown here as a comparison. The supply air mixer now shows a more reasonable result where the mixed air condition is not outside the boundary of the inlet nodes (i.e., it does not look strange).

[github-actions]

⚠️ Regressions detected on macos-14 for commit 0dd0c1c

Regression Summary

• ESO Big Diffs: 4

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on macos-14 for commit 9ea6307

Regression Summary

• ESO Big Diffs: 4

• View Results
• Download Regressions

[rraustad]

A unit test failure showed that the changes to CalcATMixer could lead to incorrect CompOnMassFlow calculation since the outlet of the inlet side ATMixer is the inlet to the VRF TU and that node condition affects the operating air mass flow rate. This code calculates a new CompOnMassFlow when an inlet side ATMixer exists.

[rraustad]

Update CalcATMixer according to changes in #11004. This change causes diffs and this branch was created to isolate those diffs associated with the refactor of this function.

[rraustad]

Eliminate state variables used only in function CalcATMixer.

[Myoldmopar]

This is very very very nice. Thanks.

[rraustad]

This unit test highlighted the fact that the inlet side ATMixer can affect the operating air mass flow rate of the VRF_FluidTCtrl model.

[github-actions]

⚠️ Regressions detected on macos-14 for commit 857b718

Regression Summary

• ESO Big Diffs: 4

• View Results
• Download Regressions

[rraustad]

Diffs on this branch are a subset of DOATo* diffs on #11004 and do not match exactly.

DOAToUnitVentilator
DOAToWaterToAirHPInlet
DOAToWaterToAirHPInlet_MultispeedFan
DOAToWaterToAirHPSupply

Example absolute diffs for DOAToUnitVentilator:

[Myoldmopar]

This is very very very nice. Thanks.

[Myoldmopar]

This is a great fix. I know you mentioned the diffs showing up here did not exactly match or complete the diffs showing in the other branch, so it will be interesting to see what the diffs look like once I merge this and develop gets pulled in there. Anyway, thanks @rraustad, always very exciting to see variables get removed from state!