Fix chiller chilling when it is off

[mjwitte]

Pull request overview

• Throw warning for chiller condition where the chiller has been shut off due to zero condenser water flow, but produces phantom cooling if the evaporator flow is > zero (probably because it's on a series-active branch). e.g. from local annual simulation for

   ** Warning ** Chiller should be off, evap flow rate=1.4389689535199999, but EvapInletTemp=7.38915769242907 is != EvapOutletTemp=6.900575452477234, EvapInletNodeNum.Temp =7.38915769242907, EvapOutletNodeNum).Temp=6.900575452477234
   **   ~~~   ** MyLoad=-833.961772284167, RunFlag=true, QEvaporator=0, QCondenser=0, EvapMassFlowRate=1.4389689535199999, CondMassFlowRate = 0, Power=0 
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=05/16 09:15 - 09:30
   ** Warning ** Chiller should be off, evap flow rate=1.4389689535199999, but EvapInletTemp=7.396212077191015 is != EvapOutletTemp=6.6766091195480035, EvapInletNodeNum.Temp =7.396212077191015, EvapOutletNodeNum).Temp=6.6766091195480035
   **   ~~~   ** MyLoad=-868.746569242984, RunFlag=true, QEvaporator=0, QCondenser=0, EvapMassFlowRate=1.4389689535199999, CondMassFlowRate = 0, Power=0 
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=05/16 09:23 - 09:30
   ** Warning ** Chiller should be off, evap flow rate=1.4389689535199999, but EvapInletTemp=7.440021886600333 is != EvapOutletTemp=6.1678902101263375, EvapInletNodeNum.Temp =7.440021886600333, EvapOutletNodeNum).Temp=6.1678902101263375
   **   ~~~   ** MyLoad=-1084.7813548033087, RunFlag=true, QEvaporator=0, QCondenser=0, EvapMassFlowRate=1.4389689535199999, CondMassFlowRate = 0, Power=0 
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=05/20 09:00 - 09:15

• Next commit fixes the issue by setting MyLoad to zero if lack of condenser water flow causes the chiller to be off. No more of the above warnings are produced (with a full annual regression).

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[mjwitte]

@rraustad @EnergyArchmage This condition occurs when the chiller has a load, but the chiller shuts down here due to zero condenser water flow and leaves calculate with

EnergyPlus/src/EnergyPlus/ChillerElectricEIR.cc

Lines 1957 to 1972 in ec7398a

	// Set initial mass flow rates
	if (this->CondenserType == DataPlant::CondenserType::WaterCooled) {
	this->CondMassFlowRate = this->CondMassFlowRateMax;
	PlantUtilities::SetComponentFlowRate(state, this->CondMassFlowRate, this->CondInletNodeNum, this->CondOutletNodeNum, this->CDPlantLoc);
	PlantUtilities::PullCompInterconnectTrigger(
	state, this->CWPlantLoc, this->CondMassFlowIndex, this->CDPlantLoc, DataPlant::CriteriaType::MassFlowRate, this->CondMassFlowRate);
	if (this->CondMassFlowRate < DataBranchAirLoopPlant::MassFlowTolerance) {
	if (this->EvapMassFlowRate < DataBranchAirLoopPlant::MassFlowTolerance) {
	// Use PlantUtilities::SetComponentFlowRate to decide actual flow
	PlantUtilities::SetComponentFlowRate(
	state, this->EvapMassFlowRate, this->EvapInletNodeNum, this->EvapOutletNodeNum, this->CWPlantLoc);
	}
	return;
	}
	}

This has been set before this exit:

EnergyPlus/src/EnergyPlus/ChillerElectricEIR.cc

Line 1939 in ec7398a

this->EvapOutletTemp = state.dataLoopNodes->Node(this->EvapOutletNodeNum).Temp;

(which seems wrong, wouldn't you want to intialize outlet=inlet before that actual calcs happen?)

After this, update thinks the chiller is on, because there is a load and the evap mass flow rate is >0 so it skips the chiller of block:

EnergyPlus/src/EnergyPlus/ChillerElectricEIR.cc

Lines 2585 to 2594 in ec7398a

	if (MyLoad >= 0 || !RunFlag) { // Chiller not running so pass inlet states to outlet states
	// Set node conditions
	state.dataLoopNodes->Node(this->EvapOutletNodeNum).Temp = state.dataLoopNodes->Node(this->EvapInletNodeNum).Temp;
	state.dataLoopNodes->Node(this->CondOutletNodeNum).Temp = state.dataLoopNodes->Node(this->CondInletNodeNum).Temp;
	if (this->CondenserType != DataPlant::CondenserType::WaterCooled) {
	state.dataLoopNodes->Node(this->CondOutletNodeNum).HumRat = state.dataLoopNodes->Node(this->CondInletNodeNum).HumRat;
	state.dataLoopNodes->Node(this->CondOutletNodeNum).Enthalpy = state.dataLoopNodes->Node(this->CondInletNodeNum).Enthalpy;
	state.dataLoopNodes->Node(this->CondInletNodeNum).MassFlowRate = 0.0;
	state.dataLoopNodes->Node(this->CondOutletNodeNum).MassFlowRate = 0.0;
	}

And those line setting condense mass flow rates to zero seem wrong, because the chiller could have flow forced through the condenser even when it's off. this is ok, it's for aircooled condenser.

[mjwitte]

Oh, never mind the condenser flow rate comment, those lines are for aircooled condenser.

[github-actions]

⚠️ Regressions detected on macos-14 for commit ce1be3e

Regression Summary

• ERR: 1

• View Results
• Download Regressions

[rraustad]

Line 1939 does seem wrong as something to do before a potential return at line 1970. Also, as an observation, if the return at 1970 happens I would think the calc routine would want to inform other later functions that the chiller RunFlag = false,

[mjwitte]

Line 1939 does seem wrong as something to do before a potential return at line 1970. Also, as an observation, if the return at 1970 happens I would think the calc routine would want to inform other later functions that the chiller RunFlag = false,

Given the arguments here

void ElectricEIRChillerSpecs::simulate(
    EnergyPlusData &state, const PlantLocation &calledFromLocation, bool FirstHVACIteration, Real64 &CurLoad, bool RunFlag)

ElectricEIRChillerSpecs::calculate(EnergyPlusData &state, Real64 &MyLoad, bool const RunFlag)

Perhaps MyLoad should be set to zero before returning?

[rraustad]

Perhaps MyLoad should be set to zero before returning?

Probably, because that return value for &CurLoad will be used by the calling routine (I think) to update the remaining load.

[rraustad]

If the calling routine does use &CurLoad then I would think that MyLoad should represent exactly what load the chiller met. I don't think I have ever considered that before.

[EnergyArchmage]

Yes, that is the idea. So it can update remaining load for dispatch to other machines if any.

[github-actions]

⚠️ Regressions detected on macos-14 for commit 41d5e18

Regression Summary

• EIO: 1
• ERR: 1
• ESO Big Diffs: 1
• Table Big Diffs: 1

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on macos-14 for commit c9e51bd

Regression Summary

• EIO: 1
• ERR: 1
• ESO Big Diffs: 1
• Table Big Diffs: 1

• View Results
• Download Regressions

[rraustad]

This does look like it boils down to this. I looked at PullCompInterconnectTrigger to see what that was trying to accomplish. This code looks like it can be deleted. I'm not asking for that to happen here but it's extra clock cycles. Removed in #10794,

    // Check to make sure we didn't reuse the index in multiple components
    if (CurCriteria.CallingCompLoopNum != plantLoc.loopNum || CurCriteria.CallingCompLoopSideNum != plantLoc.loopSideNum ||
        CurCriteria.CallingCompBranchNum != plantLoc.branchNum || CurCriteria.CallingCompCompNum != plantLoc.compNum) {
        // Diagnostic fatal: component does not properly utilize unique indexing
    }