Fix chiller chilling when it is off #10793

mjwitte · 2024-10-17T19:01:13Z

Pull request overview

Added some temporary warnings 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:

   ** 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).
Temporary warning code removed.

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mjwitte · 2024-10-17T19:16:35Z

@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 · 2024-10-17T19:17:08Z

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

github-actions · 2024-10-17T19:48:52Z

⚠️ Regressions detected on macos-14 for commit `ce1be3e`

Regression Summary

ERR: 1

rraustad · 2024-10-17T20:16:53Z

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 · 2024-10-17T20:23:18Z

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 · 2024-10-17T20:37:36Z

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 · 2024-10-17T20:51:26Z

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 · 2024-10-17T21:06:38Z

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

github-actions · 2024-10-17T21:53:44Z

⚠️ Regressions detected on macos-14 for commit `41d5e18`

Regression Summary

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

github-actions · 2024-10-18T20:05:25Z

⚠️ Regressions detected on macos-14 for commit `c9e51bd`

Regression Summary

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

rraustad · 2024-10-19T02:11:05Z

src/EnergyPlus/ChillerElectricEIR.cc

@@ -1962,6 +1962,8 @@ void ElectricEIRChillerSpecs::calculate(EnergyPlusData &state, Real64 &MyLoad, b
            state, this->CWPlantLoc, this->CondMassFlowIndex, this->CDPlantLoc, DataPlant::CriteriaType::MassFlowRate, this->CondMassFlowRate);

        if (this->CondMassFlowRate < DataBranchAirLoopPlant::MassFlowTolerance) {
+            // Shut chiller off if there is no condenser water flow
+            MyLoad = 0.0;


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 }

mjwitte · 2024-10-29T01:12:36Z

With the same fix applied to all chiller types, annual regression results:

  "diffs": {
    "big_math": [ 37 files ]
      "5ZoneCoolBeam", eso
      "5ZoneDetailedIceStorageSimpleCtrl", eso and mtr
      "5ZoneDetailedIceStorage", eso and mtr
      "5ZoneDetailedIceStorage2", eso and mtr
      "5ZoneDetailedIceStorageCubicLinear", eso and mtr
      "5ZoneIceStorage", eso and mtr
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205", eso
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205_Detailed", eso
      "ASHRAE901_OfficeLarge_STD2019_Denver_ChillerEIR", eso
      "CompSetPtControl", eso and mtr
      "FourPipeBeamLargeOffice", eso
      "FreeCoolingChiller_wWaterSideEconomizer", eso
      "IceStorage-Series-ChillerUpstream", eso
      "IceStorage-Series-ChillerDownstream", eso
      "RadLoTempHydrCtrlOpt", eso
      "RadLoTempHydrHeatCool", eso and mtr
      "RadLoTempHydrCtrlOpt2", eso
      "RadLoTempHydrHeatCoolDry", eso and mtr
      "RadLoTempHydrISOPipeHT", eso
      "SeriesActiveBranch", eso and mtr
      "RadLoTempHydrHeatCoolDryCondFD", eso
      "RadLoTempCFloHeatCoolCondFD", eso
      "TermReheatPri-SecLoop", eso
      "WaterSideEconomizer_NonIntegrated", eso and mtr
      "WaterCooledChillerWithVSCondenserControl", eso
      "RadLoTempHydrCtrlOpt3" eso and mtr
    ],
    "small_math": [ 61 files ]
    "big_table": [ 18 files ]
      "5ZoneDetailedIceStorageSimpleCtrl", 0.8% cooling electricity
      "5ZoneDetailedIceStorage", 0.8% cooling electricity
      "5ZoneDetailedIceStorage2", 0.8% cooling electricity
      "5ZoneDetailedIceStorageCubicLinear", 0.8% cooling electricity
      "5ZoneIceStorage", 0.8% cooling electricity, 1% pumps
      "ASHRAE901_OfficeLarge_STD2019_Denver", no big diffs in ABUPS, some <1% diffs in resilience and OA limits
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205", 1% heat rejection water
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205_Detailed", 1.1% heat rejection elec, 0.6% heat rejection water
      "ASHRAE901_OfficeLarge_STD2019_Denver_ChillerEIR", no big diffs in ABUPS, some 1-2% diffs in resilience and OA limits
      "CompSetPtControl", 2% cooling electricity, pumps, and heat rejection
      "ASHRAE901_Hospital_STD2019_Denver", no big diffs in ABUPS, some 1-2% diffs in resilience and OA limits
      "EMSPlantLoopOverrideControl", no big diffs in ABUPS, some 1-2% diffs in resilience and OA limits
      "FourPipeBeamLargeOffice", no big diffs in ABUPS, <1% diff in cooling electricity at peak demand
      "PythonPluginPlantLoopOverrideControl", no big diffs in ABUPS, some <1% diffs in Monthly Roof Irrigation(?)
      "RadLoTempHydrHeatCool", 3% district cooling, 0.1% cooling electricity
      "RadLoTempHydrHeatCoolDry", 3% district cooling, 0.1% cooling electricity
      "SeriesActiveBranch", no big diffs in ABUPS, some big diffs in peak electricity time bins
      "WaterSideEconomizer_NonIntegrated", 3% natural gas, 6% fans, 10% pumps, 
                       7% Setpoint Not Met During Occupied Cooling (increase from 144 to 512, hmmmmmm)
    ],
    "small_table": [ 16 files ]
    "textual": [ 30 files, some eio, some err, some both ]
      "5ZoneCoolBeam",
      "5ZoneDetailedIceStorageSimpleCtrl",
      "5ZoneDetailedIceStorage",
      "5ZoneDetailedIceStorage2",
      "5ZoneDetailedIceStorageCubicLinear",
      "5ZoneIceStorage",
      "ASHRAE901_OfficeLarge_STD2019_Denver",
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205",
      "ASHRAE901_OfficeLarge_STD2019_Denver_Chiller205_Detailed",
      "ASHRAE901_OfficeLarge_STD2019_Denver_ChillerEIR",
      "CompSetPtControl",
      "ASHRAE901_Hospital_STD2019_Denver",
      "FourPipeBeamLargeOffice",
      "IceStorage-Series-ChillerDownstream",
      "HospitalLowEnergy",
      "PlantApplicationsGuide_Example1",
      "RadLoTempHydrHeatCool",
      "RadLoTempHydrHeatCoolDry",
      "SeriesActiveBranch",
      "RadLoTempHydrHeatCoolDryCondFD",
      "WaterSideEconomizer_NonIntegrated",
      "WaterCooledChillerWithVSCondenserControl",
      "RadLoTempHydrCtrlOpt3"
    ]

github-actions · 2024-10-29T02:02:49Z

⚠️ Regressions detected on macos-14 for commit `31375e7`

Regression Summary

EIO: 16
ESO Big Diffs: 12
MTR Small Diffs: 14
Table Small Diffs: 7
Table Big Diffs: 9
ERR: 8
Table String Diffs: 4
ESO Small Diffs: 11
MTR Big Diffs: 3

mjwitte · 2024-10-29T16:02:46Z

@rraustad I'm doubting this approach now due to these results:

"WaterSideEconomizer_NonIntegrated", 3% natural gas, 6% fans, 10% pumps, 7% Setpoint Not Met During Occupied Cooling (increase from 144 to 512, hmmmmmm)

Maybe this needs to check for (gasp) flowlock before setting MyLoad=0.0? Or skip that on FirstHVACIteration?

rraustad · 2024-10-29T16:25:15Z

Well, it looked good when I reviewed this. MyLoad is disconnected from water flow rate so, for now, I think no need to look at flowlock and this is just a way to tell the plant that this component did not meet a load or what was actually met (and probably should not exceed original MyLoad?). Since this does look like the correct approach I think verifying a components operation in 1 of these files. Was this component meeting a load that it shouldn't have, or is now passing that load to another component, or is off now and the plant load increases on the next iteration? Too hard to think this through without some hard data.

mjwitte · 2024-10-29T20:28:43Z

For WaterSideEconomizer_NonIntegrated-Chiller, here are some hours where the chiller is showing evap outlet temp < evap inlet temp when the chiller is off. Develop is on the left, this branch on the right.

This file has 652 hours like that with develop, zero hours with this branch, so maybe this is fixing a real problem.
WaterSideEconomizer_NonIntegrated-Develop.zip
WaterSideEconomizer_NonIntegrated.zip

rraustad · 2024-10-29T21:13:24Z

I do think this is fixing something. Note the integrated economizer inlet now tracks the correct water temp. Why this temp changed from 10 C to 16 C is a bit of a mystery but without that free cooling the plant temps have risen. What are the plant outlet node temps wrt set point? maybe a plant outlet temp vs plant mass flow rate plot. And if the plant return water temp is > 12 C, why isn't the chiller on? is there a bypass pipe that has flow? There was no mass flow rate at the chiller before so it seems it should be off, but why? Availability Manager?

mjwitte · 2024-10-30T20:56:03Z

So, the waterside economizer HX hardly ever runs, and I haven't figured out why the chiller is off when there's a high loop demand. There's no plant availability manager, and a simple plant operating scheme with the chiller always available. There is flow through the HX on the chilled water side, but no flow on the other side of the HX. Not sure why the HX has flow if it's not contributing.

Hmmm, this is a water cooled Chiller:EngineDriven. Looking at 02/23 10:00-15:00, in both branches, the CENTRAL CHILLER:Chiller Evaporator Mass Flow Rate kg/s is zero, but there is flow on the Central Chiller Inlet/Outlet Nodes(!). The chiller is LeavingSetpointModulated, maybe that's not working right?

rraustad · 2024-10-30T21:53:05Z

@EnergyArchmage has found a few places in code where the WWHX is not passing information correctly (i.e., SafeCopyPlantNode is needed in a few places). I can't recall exactly what the details are so maybe he could comment on what you are seeing.

mjwitte added 2 commits October 17, 2024 13:49

Warn if chiller chills when off

0e0005b

Warn if chiller chills when off

e827c62

mjwitte added the Defect Includes code to repair a defect in EnergyPlus label Oct 17, 2024

Fix chiller off when condenser flow is zero

394a2c7

Revert Warn if chiller chills when off

172283a

rraustad reviewed Oct 19, 2024

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Fix chiller off when condenser flow is zero for all other chillers

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Fix chiller chilling when it is off #10793

Fix chiller chilling when it is off #10793

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Fix chiller chilling when it is off #10793

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⚠️ Regressions detected on macos-14 for commit ce1be3e

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⚠️ Regressions detected on macos-14 for commit 41d5e18

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⚠️ Regressions detected on macos-14 for commit c9e51bd

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⚠️ Regressions detected on macos-14 for commit 31375e7

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⚠️ Regressions detected on macos-14 for commit `ce1be3e`

⚠️ Regressions detected on macos-14 for commit `41d5e18`

⚠️ Regressions detected on macos-14 for commit `c9e51bd`

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⚠️ Regressions detected on macos-14 for commit `31375e7`

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