Update NFP and implement/test thermosiphon model

design/FY2024/NFP-Refrigerant-Migration-Decarbonization.md

@@ -7,6 +7,7 @@ New Feature for Plant Decarbonization
 **Florida Solar Energy Center***
 
  - Original Date: Feb 27, 2024
+ - Final NFP - updated Apr 9, 2024
 
 ## Justification for Feature Update
 
@@ -37,35 +38,36 @@ Figure 1. Operating envelope and conditions for refrigerant migration
 
 ### Approach
 
-This feature proposes to add 2 optional fields to chillers representing the refrigerant migration empirical model. Tentatively at the end of the object but these fields could be inserted near the capacity and COP inputs if that seems better placement. The curve is likely the only required input field to denote the use of this equipment enhancement (i.e., the resulting curve fraction will determine if the chiller can meet the load using only refrigerant migration), however, the zero crossing of the performance curve may not accurately represent the actual operating range and an additional field is suggested as Refrigerant Migration Minimum Temperature Difference (see following example for HeatPump:PlantLoop:EIR:Cooling). It is anticipated that both of these fields will be implemented in each chiller type.
+This feature proposes to add 2 optional fields to chillers representing the refrigerant migration (or generically a thermosiphon for passive heat exchange) empirical model. Tentatively at the end of the object but these fields could be inserted near the capacity and COP inputs if that seems better placement. The curve is likely the only required input field to denote the use of this equipment enhancement (i.e., the resulting curve fraction will determine if the chiller can meet the load using only refrigerant migration), however, the zero crossing of the performance curve may not accurately represent the actual operating range and an additional field is suggested as Refrigerant Migration Minimum Temperature Difference (see following example for HeatPump:PlantLoop:EIR:Cooling). It is anticipated that both of these fields will be implemented in each chiller type.
 
 ```
 HeatPump:PlantLoop:EIR:Cooling,
-  A13, \field Refrigerant Migration Temperature Difference Curve Name
+  A13, \field Thermosiphon Temperature Difference Curve Name
        \type object-list
        \object-list UniVariateFunctions
        \note quadratic curve = a + b * dT is typical, other univariate curves may be used
-  N10; \field Refrigerant Migration Minimum Temperature Difference
+       \note dT = evaporator outlet temperature minus condenser inlet temperature
+  N10; \field Thermosiphon Minimum Temperature Difference
        \type real
-       \minimum>=0
+       \minimum 0.0
        \default 0.0
-       \note refirgerant migration is disabled below this minimum limit and
+       \note thermosiphon model is disabled below this minimum limit and
        \note when the load is greater than calculated using the prevoius field.
 
 Chiller:Electric,
-  A14; \field Refrigerant Migration Temperature Difference Curve Name
+  A14; \field Thermosiphon Temperature Difference Curve Name
        \type object-list
        \object-list UniVariateFunctions
        \note quadratic curve = a + b * dT is typical, other univariate curves may be used
 
 Chiller:Electric:EIR,
-  A17; \field Refrigerant Migration Temperature Difference Curve Name
+  A17; \field Thermosiphon Temperature Difference Curve Name
        \type object-list
        \object-list UniVariateFunctions
        \note quadratic curve = a + b * dT is typical, other univariate curves may be used
 
 Chiller:Electric:Reformulated:EIR,
-  A16; \field Refrigerant Migration Temperature Difference Curve Name
+  A16; \field Thermosiphon Temperature Difference Curve Name
        \type object-list
        \object-list UniVariateFunctions
        \note quadratic curve = a + b * dT is typical, other univariate curves may be used

doc/input-output-reference/src/overview/group-plant-equipment.tex

@@ -5451,6 +5451,14 @@ \subsubsection{Inputs}\label{plhp_eir_cooling_inputs}
 
 This optional alpha field specifies the name of a univariate curve or table that defines the maximum supply water temperature.
 
+\paragraph{Field: Thermosiphon Temperature Difference Curve Name}\label{plhp_eir_cooling_inputs_thermosiphon_temperature_difference_curve_name}
+
+This optional alpha field specifies the name of a univariate curve or table that defines the thermosiphon capacity fraction as a function of temperature difference between the load side outlet node and source side inlet node. If this field is blank, the thermosiphon model is disabled.
+
+\paragraph{Field: Thermosiphon Minimum Temperature Difference}\label{plhp_eir_cooling_inputs_thermosiphon_minimum_temperature_difference}
+
+This optional numeric field specifies the temperature difference above which the thermosiphon model is active. The default value is 0. Above this temperature difference the heat pump compressor will be off.
+
 \subsection{HeatPump:PlantLoop:EIR:Heating}\label{plhp_eir_heating}
 
 The EIR-formulated heating model objects are described.
@@ -5696,6 +5704,13 @@ \subsubsection{Outputs}\label{plhp_eir_outputs}
     HVAC,Average,Heat Pump Source Side Mass Flow Rate {[}kg/s{]}
 \end{itemize}
 
+Outputs specific to HeatPump:PlantLoop:EIR:Cooling
+
+\begin{itemize}
+    \item
+    HVAC,Average,Heat Pump Thermosiphon Status  {[}{]}
+\end{itemize}
+
 Outputs specific to HeatPump:PlantLoop:EIR:Heating
 
 \begin{itemize}

idd/Energy+.idd.in

@@ -74991,11 +74991,24 @@ HeatPump:PlantLoop:EIR:Cooling,
         \object-list UniVariateFunctions
         \note quadratic curve = a + b*OAT is typical, other univariate curves may be used
         \note OAT = Outdoor Dry-Bulb Temperature
-   N10; \field Maximum Supply Water Temperature Curve Name
+   N10, \field Maximum Supply Water Temperature Curve Name
         \type object-list
         \object-list UniVariateFunctions
         \note quadratic curve = a + b*OAT is typical, other univariate curves may be used
         \note OAT = Outdoor Dry-Bulb Temperature
+   A13, \field Thermosiphon Temperature Difference Curve Name
+        \type object-list
+        \object-list UniVariateFunctions
+        \note quadratic curve = a + b * dT is typical, other univariate curves may be used
+        \note dT = evaporator outlet temperature minus condenser inlet temperature
+        \note If this field is blank the thermosiphon model is disabled.
+   N11; \field Thermosiphon Minimum Temperature Difference
+        \type real
+        \minimum 0.0
+        \default 0.0
+        \note Thermosiphon model is disabled below this minimum limit and
+        \note when the load is greater than calculated using the prevoius field.
+
 
 HeatPump:PlantLoop:EIR:Heating,
         \memo An EIR formulated water to water heat pump model, heating operation

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

@@ -195,6 +195,7 @@ void EIRPlantLoopHeatPump::resetReportingVariables()
     this->partLoadRatio = 0.0;
     this->cyclingRatio = 0.0;
     this->defrostPowerMultiplier = 1.0;
+    this->thermosiphonStatus = 0;
 }
 
 void EIRPlantLoopHeatPump::setOperatingFlowRatesWSHP(EnergyPlusData &state, bool FirstHVACIteration)
@@ -375,6 +376,7 @@ void EIRPlantLoopHeatPump::doPhysicsASHP(EnergyPlusData &state, Real64 currentLo
 
 void EIRPlantLoopHeatPump::calcAvailableCapacity(EnergyPlusData &state, Real64 const currentLoad, Real64 &availableCapacity, Real64 &partLoadRatio)
 {
+    this->thermosiphonStatus = 0;
     // get setpoint on the load side outlet
     Real64 loadSideOutletSetpointTemp = this->getLoadSideOutletSetPointTemp(state);
     Real64 originalLoadSideOutletSPTemp = loadSideOutletSetpointTemp;
@@ -507,8 +509,10 @@ void EIRPlantLoopHeatPump::calcPowerUsage(EnergyPlusData &state)
     this->eirModCurveCheck(state, eirModifierFuncTemp, eirModifierFuncPLR);
 
     // compute power usage
-    this->powerUsage = (this->loadSideHeatTransfer / this->referenceCOP) * eirModifierFuncPLR * eirModifierFuncTemp * this->defrostPowerMultiplier *
-                       this->cyclingRatio;
+    if (this->thermosiphonDisabled(state)) {
+        this->powerUsage = (this->loadSideHeatTransfer / this->referenceCOP) * eirModifierFuncPLR * eirModifierFuncTemp *
+                           this->defrostPowerMultiplier * this->cyclingRatio;
+    }
 }
 
 void EIRPlantLoopHeatPump::calcSourceSideHeatTransferWSHP(EnergyPlusData &state)
@@ -1450,6 +1454,16 @@ void EIRPlantLoopHeatPump::processInputForEIRPLHP(EnergyPlusData &state)
                     thisPLHP.maxSupplyWaterTempCurveIndex =
                         Curve::GetCurveIndex(state, Util::makeUPPER(maximumSupplyWaterTempCurveName.value().get<std::string>()));
                 }
+                // fields only in cooling object
+                if (thisPLHP.EIRHPType == DataPlant::PlantEquipmentType::HeatPumpEIRCooling) {
+                    auto const thermosiphonTempCurveName = fields.find("thermosiphon_temperature_difference_curve_name");
+                    if (thermosiphonTempCurveName != fields.end()) {
+                        thisPLHP.thermosiphonTempCurveIndex =
+                            Curve::GetCurveIndex(state, Util::makeUPPER(thermosiphonTempCurveName.value().get<std::string>()));
+                    }
+                    thisPLHP.thermosiphonMinTempDiff = state.dataInputProcessing->inputProcessor->getRealFieldValue(
+                        fields, schemaProps, "thermosiphon_minimum_temperature_difference");
+                }
 
                 std::string flowControlTypeName =
                     Util::makeUPPER(state.dataInputProcessing->inputProcessor->getAlphaFieldValue(fields, schemaProps, "flow_mode"));
@@ -1788,6 +1802,13 @@ void EIRPlantLoopHeatPump::oneTimeInit(EnergyPlusData &state)
                                 OutputProcessor::Group::Plant,
                                 OutputProcessor::EndUseCat::Cooling,
                                 "Heat Pump");
+            SetupOutputVariable(state,
+                                "Heat Pump Thermosiphon Status",
+                                Constant::Units::None,
+                                this->thermosiphonStatus,
+                                OutputProcessor::TimeStepType::System,
+                                OutputProcessor::StoreType::Average,
+                                this->name);
         } else if (this->EIRHPType == DataPlant::PlantEquipmentType::HeatPumpEIRHeating) { // energy from HeatPump:PlantLoop:EIR:Heating object
             SetupOutputVariable(state,
                                 "Heat Pump Electricity Energy",
@@ -1929,6 +1950,27 @@ void EIRPlantLoopHeatPump::oneTimeInit(EnergyPlusData &state)
     }
 }
 
+bool EIRPlantLoopHeatPump::thermosiphonDisabled(EnergyPlusData &state)
+{
+    if (this->thermosiphonTempCurveIndex > 0) {
+        this->thermosiphonStatus = 0;
+        Real64 dT = this->loadSideOutletTemp - this->sourceSideInletTemp;
+        if (dT < this->thermosiphonMinTempDiff) {
+            return true;
+        }
+        Real64 thermosiphonCapFrac = Curve::CurveValue(state, this->thermosiphonTempCurveIndex, dT);
+        Real64 capFrac = this->partLoadRatio * this->cyclingRatio;
+        if (thermosiphonCapFrac > capFrac && this->loadSideHeatTransfer > 0.0) {
+            this->thermosiphonStatus = 1;
+            this->powerUsage = 0.0;
+            return false;
+        }
+        return true;
+    } else {
+        return true;
+    }
+}
+
 void EIRPlantLoopHeatPump::report(EnergyPlusData &state)
 {
 

src/EnergyPlus/PlantLoopHeatPumpEIR.hh

@@ -208,6 +208,11 @@ namespace EIRPlantLoopHeatPumps {
         Real64 maxOutdoorTemperatureDefrost = 0.0;
         Real64 defrostPowerMultiplier = 1.0; // defrost power adjustment factor
 
+        // thermosiphon model
+        int thermosiphonTempCurveIndex = 0;
+        Real64 thermosiphonMinTempDiff = 0.0;
+        int thermosiphonStatus = 0;
+
         // a couple worker functions to easily allow merging of cooling and heating operations
         std::function<Real64(Real64, Real64)> calcLoadOutletTemp;
         std::function<Real64(Real64, Real64)> calcQsource;
@@ -291,6 +296,8 @@ namespace EIRPlantLoopHeatPumps {
         void isPlantInletOrOutlet(EnergyPlusData &state);
 
         void oneTimeInit(EnergyPlusData &state) override;
+
+        bool thermosiphonDisabled(EnergyPlusData &state);
     };
 
     struct EIRFuelFiredHeatPump : public EIRPlantLoopHeatPump

testfiles/PlantLoopHeatPump_EIR_LargeOffice-2-AWHP-AuxBoiler-Pri-Sec-4PipeBeam.idf

@@ -8441,7 +8441,13 @@
     EIRCurveFuncPLR,         !- Electric Input to Output Ratio Modifier Function of Part Load Ratio Curve Name
     Setpoint,                    !- Control Type
     VariableSpeedPumping,            !- Flow Mode
-    0.2;                     !- Minimum Part Load Ratio
+    0.2,                     !- Minimum Part Load Ratio
+    ,                        !- Minimum Source Inlet Temperature
+    ,                        !- Maximum Source Inlet Temperature
+    ,                        !- Minimum Supply Water Temperature Curve Name
+    ,                        !- Maximum Supply Water Temperature Curve Name
+    ThermosiphonCurve,       !- Thermosiphon Temperature Difference Curve Name
+    2.0;                     !- Thermosiphon Minimum Temperature Difference
 
   OutdoorAir:Node,
     AWHP_1 Cooling Side Condenser Air Inlet Node,
@@ -8465,7 +8471,22 @@
     EIRCurveFuncPLR,         !- Electric Input to Output Ratio Modifier Function of Part Load Ratio Curve Name
     Setpoint,                    !- Control Type
     VariableSpeedPumping,            !- Flow Mode
-    0.2;                     !- Minimum Part Load Ratio
+    0.2,                     !- Minimum Part Load Ratio
+    ,                        !- Minimum Source Inlet Temperature
+    ,                        !- Maximum Source Inlet Temperature
+    ,                        !- Minimum Supply Water Temperature Curve Name
+    ,                        !- Maximum Supply Water Temperature Curve Name
+    ThermosiphonCurve,       !- Thermosiphon Temperature Difference Curve Name
+    2.0;                     !- Thermosiphon Minimum Temperature Difference
+
+  Curve:Linear,
+    ThermosiphonCurve,       !- Name
+    0,                       !- Coefficient1 Constant
+    0.06,                    !- Coefficient2 x
+    0,                       !- Minimum Value of x
+    30.0,                    !- Maximum Value of x
+    0.0,                     !- Minimum Curve Output
+    1.0;                     !- Maximum Curve Output
 
 !- ACX 140 Biquadratic cooling curves provided by Trane 
 Curve:Biquadratic,
@@ -10315,6 +10336,7 @@ Curve:Biquadratic,
   Output:Variable,*,Heat Pump Electricity Rate,hourly; !- HVAC Average [W]
   Output:Variable,*,Heat Pump Load Side Mass Flow Rate,hourly; !- HVAC Average [kg/s]
   Output:Variable,*,Heat Pump Source Side Mass Flow Rate,hourly; !- HVAC Average [kg/s]
+  Output:Variable,*,Heat Pump Thermosiphon Status,hourly; !- HVAC Average [kg/s]
 
   Output:Variable,*,Boiler Heating Rate,hourly; !- HVAC Average [W]
   Output:Variable,*,Boiler Inlet Temperature,hourly; !- HVAC Average [C]