Enhancement to crankcase heater #9949

yujiex · 2023-04-11T20:52:03Z

Pull request overview

Crankcase heaters use a simple electrical circuit to create heat within the crankcase when the compressor of the chiller or heat pump is not in use. The heat keeps the refrigerant from condensing and prevents the refrigerant from migrating through the seals into the oil. Poor control of the crankcase heater could result in excessive energy consumption. Some of the existing products start to provide variable heater power based on different outdoor temperature conditions. Currently, EnergyPlus can only model a constant power crankcase heater with a temperature cutoff. This feature proposes to enhance the crankcase heater in EnergyPlus to allow for variable heater power, which enables to model realistic performance of heat pumps.

Fixes Non-matching field name and value in error messages #10137

testing with a testfile

Running HeatPump_variableCrankcaseHeaterCapacity.idf, with a crankcase heater capacity curve of y = 60 - 2x. The following plot shows the relationship between outdoor temperature and heating coil crankcase heater electricity rate, limited to the time period with runtime fraction = 0.

The following is the simulation result of HeatPumpVSAS_variableCrankcaseHeaterCapacity.idf with variable speed coils using the same crankcase heater capacity curve. Column C computes the crankcase heater power before adjusting for the runtime fraction

Comparing output of a HeatPumpVSAS.idf and HeatPumpVSAS_variableCrankcaseHeaterCapacity.idf with constant curve

!- crankcase heater capacity in HeatPumpVSAS.idf 
  Coil:Heating:DX:VariableSpeed,
    Heat Pump DX Heating Coil 1,  !- Name
    Heating Coil Air Inlet Node,  !- Indoor Air Inlet Node Name
    SuppHeating Coil Air Inlet Node,  !- Indoor Air Outlet Node Name
    10.0,                    !- Number of Speeds {dimensionless}
    10.0,                    !- Nominal Speed Level {dimensionless}
    35000,                   !- Rated Heating Capacity At Selected Nominal Speed Level {W}
    1.7,                     !- Rated Air Flow Rate At Selected Nominal Speed Level {m3/s}
    HPACCOOLPLFFPLR,         !- Energy Part Load Fraction Curve Name
    ,                        !- Defrost Energy Input Ratio Function of Temperature Curve Name
    -5.0,                    !- Minimum Outdoor Dry-Bulb Temperature for Compressor Operation {C}
    ,                        !- Outdoor Dry-Bulb Temperature to Turn On Compressor {C}
    5.0,                     !- Maximum Outdoor Dry-Bulb Temperature for Defrost Operation {C}
    200.0,                   !- Crankcase Heater Capacity {W}


!- curve in HeatPumpVSAS_variableCrankcaseHeaterCapacity.idf
  Curve:Linear,
    heaterCapCurve,          !- Name
    200.0,                    !- Coefficient1 Constant
    0.0,                     !- Coefficient2 x
    -80,                     !- Minimum Value of x
    80;                      !- Maximum Value of x

As anticipated, the crankcase heater power are the same for the two cases

Comparing a curve with a constant capacity of 200 and a curve with a constant capacity of 100

Summary of some identified issues

1. The crankcase heater for the variable speed heat pump water heater might be off all the time

In the file VariableSpeedCoils.cc, the following chunk of code (in the function CalcVarSpeedHPWH) here modifies the temporary variable CrankcaseHeatingPower which is then used in the calculation of state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).CrankcaseHeaterPower later on. It seems that the check of whether the temperature is appropriate for the crankcase heater to operate is only executed when EvapInletNode is 0. But this variable gets value from state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).AirInletNodeNum which is from a required field. So it can’t be 0 in normal cases. This might mean the crankcase heater power will always be 0

        // check if indoor evaporator or outdoor evaporator
        CrankcaseHeatingPower = 0.0;
        if (EvapInletNode != 0) {
            state.dataVariableSpeedCoils->LoadSideInletDBTemp = state.dataLoopNodes->Node(EvapInletNode).Temp;
            state.dataVariableSpeedCoils->LoadSideInletHumRat = state.dataLoopNodes->Node(EvapInletNode).HumRat;
            LoadPressure = state.dataLoopNodes->Node(EvapInletNode).Press;
            // prevent the air pressure not given
            if (LoadPressure < 10.0) LoadPressure = state.dataEnvrn->OutBaroPress;

            state.dataVariableSpeedCoils->LoadSideInletWBTemp = state.dataLoopNodes->Node(EvapInletNode).OutAirWetBulb;
            state.dataVariableSpeedCoils->LoadSideInletEnth = state.dataLoopNodes->Node(EvapInletNode).Enthalpy;
        } else {
            state.dataVariableSpeedCoils->LoadSideInletDBTemp = state.dataEnvrn->OutDryBulbTemp;
            state.dataVariableSpeedCoils->LoadSideInletHumRat = state.dataEnvrn->OutHumRat;
            LoadPressure = state.dataEnvrn->OutBaroPress;
            state.dataVariableSpeedCoils->LoadSideInletWBTemp = state.dataEnvrn->OutWetBulbTemp;
            state.dataVariableSpeedCoils->LoadSideInletEnth = state.dataEnvrn->OutEnthalpy;

            // Initialize crankcase heater, operates below OAT defined in input deck for HP DX heating coil
            if (state.dataEnvrn->OutDryBulbTemp < state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).MaxOATCrankcaseHeater) {
                CrankcaseHeatingPower = state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).CrankcaseHeaterCapacity;
                if (state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).CrankcaseHeaterCapacityCurveIndex > 0) {
                    CrankcaseHeatingPower = Curve::CurveValue(state,
                                                              state.dataVariableSpeedCoils->VarSpeedCoil(DXCoilNum).CrankcaseHeaterCapacityCurveIndex,
                                                              state.dataEnvrn->OutDryBulbTemp);
                }
            };
        }

2. Some inconsistency in what temperature should be compared to the maximum temperature threshold below which the crankcase heater should operate

See this issue: #10052

NOTE: ENHANCEMENTS MUST FOLLOW A SUBMISSION PROCESS INCLUDING A FEATURE PROPOSAL AND DESIGN DOCUMENT PRIOR TO SUBMITTING CODE

Pull Request Author

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

Reviewer

This will not be exhaustively relevant to every PR.

mjwitte

@yujiex A few comments below. Also, I don't see any doc changes yet.

mjwitte · 2023-04-28T17:05:28Z

idd/Energy+.idd.in

@@ -51383,6 +51383,10 @@ Coil:Cooling:DX:CurveFit:Performance,
       \note is used as Reheat mode.
       \type object-list
       \object-list DXCoolingOperatingModeNames
+   A8; \field Outdoor Temperature Dependent Crankcase Heater Capacity Curve Name


To be consistent with other curve names this should be
"Crankcase Heater Capacity Function of Temperature Curve Name"
ref.
Coil:Cooling:DX:SingleSpeed, Total Cooling Capacity Function of Temperature Curve Name
Coil:Cooling:DX:CurveFit:Speed, Total Cooling Capacity Modifier Function of Temperature Curve Name

Also this should be tagged with

\type object-list \object-list UnivariateFunctions

Right, I'll change the name to "Crankcase Heater Capacity Function of Temperature Curve Name" to match the existing patterns and add the object-list tag.

Right, I'll change the name to "Crankcase Heater Capacity Function of Temperature Curve Name" to match the existing patterns and add the object-list tag.

These changes are still needed. Also, for each affected object, \min-fields should be increased by one (unless the new field is already beyond the current min-fields value).

right right, I'll change min-fields too for ones too for those with the new curve field not beyond the current min-field.

mjwitte · 2023-04-28T17:09:34Z

idd/Energy+.idd.in

        \type object-list
        \object-list UnivariateFunctions
        \note quadratic curve = a + b*ffa + c*ffa**2
        \note cubic curve = a + b*ffa + c*ffa**2 + d*ffa**3
        \note ffa = Fraction of the full load Air Flow
+   A50; \field Outdoor Temperature Dependent Crankcase Heater Capacity Curve Name


Hmm, the group of speed fields is currently not extensible, so technically, this is ok to add at the end of the object, but it just seems lost here. @Myoldmopar do we care?

Yeah, I'm not certain whether I should put it at the end or near the other crankcase heater fields.

mjwitte · 2023-04-28T17:12:00Z

src/EnergyPlus/Coils/CoilCoolingDXCurveFitPerformance.hh

@@ -117,6 +118,7 @@ struct CoilCoolingDXCurveFitPerformance
    std::string name;
    Real64 crankcaseHeaterCap = 0.0;
    Real64 crankcaseHeaterPower = 0.0;
+    Real64 crankcaseHeaterCapacityCurveIndex = 0.0;


It was fixed in another commit. I'll push it soon. I was trying to figure out some issues with the variable speed coils curve application.

It was fixed in another commit.

This is still not an integer. Did you by chance forget to push a commit?

mjwitte · 2023-04-28T17:15:06Z

tst/EnergyPlus/unit/Coils/CoilCoolingDXCurveFitOperatingMode.unit.cc

+    EXPECT_EQ("COIL COOLING DX 1", thisCoil.name);
+    EXPECT_EQ("COIL COOLING DX CURVE FIT PERFORMANCE 1", thisCoil.performance.name);
+    EXPECT_EQ("HEATERCAPCURVE", Curve::GetCurveName(*state, thisCoil.performance.crankcaseHeaterCapacityCurveIndex));
+}


Add a return to the last line.

an explicit return like this return;? @mjwitte

Sorry, no, a return. Look at the display in the PR and you'll see a red circle at the end, because the last line of the file is not terminated fully.

Oh! I understand now. I'll add a new line in the end.

mjwitte · 2023-04-28T17:17:05Z

tst/EnergyPlus/unit/DXCoils.unit.cc

+        ",",
+        ",",
+        ",",
+        ",",
+        ",",
+        ",",
+        ",",
+        ",",
+        "heaterCapCurve5;                          !- Outdoor Temperature Dependent Crankcase Heater Capacity Curve Name",


And this shows why the new field should be placed before the speed groups for variable speed and multi-speed coils, even if it forces a transition rule. @Myoldmopar ?

yeah, this is kind of tedious.

mjwitte · 2023-04-28T17:34:17Z

src/EnergyPlus/Coils/CoilCoolingDXCurveFitPerformance.cc

+    if (!input_data.outdoor_temperature_dependent_crankcase_heater_capacity_curve_name.empty()) {
+        this->crankcaseHeaterCapacityCurveIndex =
+            Curve::GetCurveIndex(state, input_data.outdoor_temperature_dependent_crankcase_heater_capacity_curve_name);
+    }


The input processing needs more steps here (and everywhere) to check if a valid curve was found and to check the curve dimensions. For example, see here. For this application, any uni-variate curve or table is acceptable.

good point. I'll add in the curve validations.

nrel-bot-2 · 2023-05-06T00:15:24Z

@yujiex it has been 7 days since this pull request was last updated.

nrel-bot-2b · 2023-05-13T00:30:21Z

@yujiex it has been 7 days since this pull request was last updated.

nrel-bot-2c · 2023-05-20T00:08:17Z

@yujiex it has been 7 days since this pull request was last updated.

nrel-bot-2 · 2023-05-20T00:17:07Z

@yujiex it has been 7 days since this pull request was last updated.

rraustad · 2023-08-04T20:37:34Z

src/EnergyPlus/DXCoils.cc

                } else {
                    ShowSevereError(state, format("{}{}=\"{}\", invalid", RoutineName, CurrentModuleObject, thisDXCoil.Name));
-                    ShowContinueError(state, format("...not found {}=\"{}\".", cAlphaFields(12 + (I - 1) * 6), Alphas(15 + (I - 1) * 6)));
+                    ShowContinueError(state, format("...not found {}=\"{}\".", cAlphaFields(13 + (I - 1) * 6), Alphas(13 + (I - 1) * 6)));


Was this a mistake in code and was corrected? I see an alpha index of 12 and 15 before, and now I see 13 and 13. If this fixes a mistake, which it looks like it does, then that should be added to the PR description.

It should probably be 13 as the error message was stating what the current value of this field is, so the cAlphaFields and Alphas should have the same index. The 12th (one before) and 14th (one after) fields also have similar formats. So I corrected it.

rraustad · 2023-08-04T20:45:44Z

src/EnergyPlus/DXCoils.cc

@@ -9319,6 +9401,9 @@ void CalcDoe2DXCoil(EnergyPlusData &state,
    // If used in a heat pump, the value of MaxOAT in the heating coil overrides that in the cooling coil (in GetInput)
    if (CompAmbTemp < thisDXCoil.MaxOATCrankcaseHeater) {
        CrankcaseHeatingPower = thisDXCoil.CrankcaseHeaterCapacity;
+        if (thisDXCoil.CrankcaseHeaterCapacityCurveIndex > 0) {
+            CrankcaseHeatingPower *= Curve::CurveValue(state, thisDXCoil.CrankcaseHeaterCapacityCurveIndex, CompAmbTemp);
+        }


This code could have probably been added to ReportDXCoil, instead of each calc funtion. It's OK as is, just noting an alternate way to account for the curve value.

yeah, I do see a lot of places with this type of calculation.

rraustad · 2023-08-04T20:50:19Z

src/EnergyPlus/DXCoils.hh

+        Real64 CrankcaseHeaterCapacity;        // total crankcase heater capacity [W]
+        Real64 CrankcaseHeaterPower;           // report variable for average crankcase heater power [W]
+        Real64 MaxOATCrankcaseHeater;          // maximum OAT for crankcase heater operation [C]
+        int CrankcaseHeaterCapacityCurveIndex; // Crankcase heater power-temperature curve or table index


I am not suggesting a change here, but when adding new struct varaiables, declare inline (i.e., = 0) instead of adding to the constructor. Better yet, delete the constructor and decalre everything inline.

make sense. Should probably gradually phase these out and use inline.

rraustad · 2023-08-04T20:53:56Z