Add thermosiphon to Chiller:Electric

idd/Energy+.idd.in

@@ -73968,11 +73968,24 @@ Chiller:Electric,
        \note Using this triggers a model more suited to series bundle and chillers with higher temperature heat recovery
        \note If this field is not used, the bundles are modeled as being in parallel
        \type node
-  A13; \field End-Use Subcategory
+  A13, \field End-Use Subcategory
        \note Any text may be used here to categorize the end-uses in the ABUPS End Uses by Subcategory table.
        \type alpha
        \retaincase
        \default General
+  A14, \field Thermosiphon Temperature Difference Curve Name
+       \type object-list
+       \object-list UniVariateFunctions
+       \note quadratic curve = a + b * (Tevap, out - Tcond, in) is typical, other univariate curves may be used
+       \note Tevap, out = evaporator outlet temperature
+       \note Tcond, in = condenser inlet temperature
+       \note If this field is blank the thermosiphon model is disabled.
+  N26; \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.
 
 Chiller:Absorption:Indirect,
    \min-fields 17
@@ -75307,8 +75320,9 @@ HeatPump:PlantLoop:EIR:Cooling,
    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
-        \note dT = evaporator outlet temperature minus condenser inlet temperature
+        \note quadratic curve = a + b * (Tevap, out - Tcond, in) is typical, other univariate curves may be used
+        \note Tevap, out = evaporator outlet temperature
+        \note Tcond, in = condenser inlet temperature
         \note If this field is blank the thermosiphon model is disabled.
    N13; \field Thermosiphon Minimum Temperature Difference
         \type real

src/EnergyPlus/PlantChillers.cc

@@ -595,19 +595,24 @@ namespace PlantChillers {
             if (!state.dataIPShortCut->lAlphaFieldBlanks(10)) {
                 thisChiller.BasinHeaterSchedulePtr = ScheduleManager::GetScheduleIndex(state, state.dataIPShortCut->cAlphaArgs(10));
                 if (thisChiller.BasinHeaterSchedulePtr == 0) {
-                    ShowWarningError(state,
-                                     format("{}, \"{}\" TRIM(state.dataIPShortCut->cAlphaFieldNames(10)) \"{}\" was not found. Basin heater "
-                                            "operation will not be modeled and the simulation continues",
-                                            state.dataIPShortCut->cCurrentModuleObject,
-                                            thisChiller.Name,
-                                            state.dataIPShortCut->cAlphaArgs(10)));
+                    ShowWarningError(
+                        state,
+                        format("{}, \"{}\" {} \"{}\" was not found. Basin heater operation will not be modeled and the simulation continues",
+                               state.dataIPShortCut->cCurrentModuleObject,
+                               thisChiller.Name,
+                               state.dataIPShortCut->cAlphaFieldNames(10),
+                               state.dataIPShortCut->cAlphaArgs(10)));
                 }
             }
             if (NumAlphas > 12) {
                 thisChiller.EndUseSubcategory = state.dataIPShortCut->cAlphaArgs(13);
             } else {
                 thisChiller.EndUseSubcategory = "General";
             }
+            if (!state.dataIPShortCut->lAlphaFieldBlanks(14)) {
+                thisChiller.thermosiphonTempCurveIndex = Curve::GetCurveIndex(state, Util::makeUPPER(state.dataIPShortCut->cAlphaArgs(14)));
+            }
+            thisChiller.thermosiphonMinTempDiff = state.dataIPShortCut->rNumericArgs(26);
         }
 
         if (ErrorsFound) {
@@ -705,6 +710,13 @@ namespace PlantChillers {
                             OutputProcessor::TimeStepType::System,
                             OutputProcessor::StoreType::Average,
                             this->Name);
+        SetupOutputVariable(state,
+                            "Thermosiphon Status",
+                            Constant::Units::None,
+                            this->thermosiphonStatus,
+                            OutputProcessor::TimeStepType::System,
+                            OutputProcessor::StoreType::Average,
+                            this->Name);
 
         // Condenser mass flow and outlet temp are valid for water cooled
         if (this->CondenserType == DataPlant::CondenserType::WaterCooled) {
@@ -1385,6 +1397,7 @@ namespace PlantChillers {
         this->EvaporatorEnergy = 0.0;
         this->QHeatRecovered = 0.0;
         this->ActualCOP = 0.0;
+        this->thermosiphonStatus = 0;
 
         //   calculate end time of current time step
         Real64 CurrentEndTime = state.dataGlobal->CurrentTime + state.dataHVACGlobal->SysTimeElapsed;
@@ -1574,6 +1587,7 @@ namespace PlantChillers {
         } else {
             OperPartLoadRat = 0.0;
         }
+        this->CyclingRatio = OperPartLoadRat;
 
         Real64 Cp = FluidProperties::GetSpecificHeatGlycol(state,
                                                            state.dataPlnt->PlantLoop(this->CWPlantLoc.loopNum).FluidName,
@@ -1587,13 +1601,15 @@ namespace PlantChillers {
             this->PossibleSubcooling =
                 DataPlant::CompData::getPlantComponent(state, this->CWPlantLoc).CurOpSchemeType != DataPlant::OpScheme::CompSetPtBased;
             this->QEvaporator = AvailChillerCap * OperPartLoadRat;
-            Real64 FRAC;
+            Real64 FRAC = 0.0;
             if (OperPartLoadRat < this->MinPartLoadRat) {
                 FRAC = min(1.0, (OperPartLoadRat / this->MinPartLoadRat));
             } else {
                 FRAC = 1.0;
             }
-            this->Power = FracFullLoadPower * FullLoadPowerRat * AvailChillerCap / this->COP * FRAC;
+            if (this->thermosiphonDisabled(state)) {
+                this->Power = FracFullLoadPower * FullLoadPowerRat * AvailChillerCap / this->COP * FRAC;
+            }
 
             // Either set the flow to the Constant value or calculate the flow for the variable volume
             if ((this->FlowMode == DataPlant::FlowMode::Constant) || (this->FlowMode == DataPlant::FlowMode::NotModulated)) {
@@ -1784,16 +1800,17 @@ namespace PlantChillers {
                     this->EvapOutletTemp = state.dataLoopNodes->Node(this->EvapInletNodeNum).Temp;
                 }
             }
-
-            Real64 FRAC;
+            Real64 FRAC = 0.0;
             if (OperPartLoadRat < this->MinPartLoadRat) {
                 FRAC = min(1.0, (OperPartLoadRat / this->MinPartLoadRat));
             } else {
                 FRAC = 1.0;
             }
 
             // Chiller is false loading below PLR = minimum unloading ratio, find PLR used for energy calculation
-            this->Power = FracFullLoadPower * FullLoadPowerRat * AvailChillerCap / this->COP * FRAC;
+            if (this->thermosiphonDisabled(state)) {
+                this->Power = FracFullLoadPower * FullLoadPowerRat * AvailChillerCap / this->COP * FRAC;
+            }
 
             if (this->EvapMassFlowRate == 0.0) {
                 this->QEvaporator = 0.0;
@@ -2120,6 +2137,26 @@ namespace PlantChillers {
             this->MyFlag = false;
         }
     }
+    bool ElectricChillerSpecs::thermosiphonDisabled(EnergyPlusData &state)
+    {
+        if (this->thermosiphonTempCurveIndex > 0) {
+            this->thermosiphonStatus = 0;
+            Real64 dT = this->EvapOutletTemp - this->CondInletTemp;
+            if (dT < this->thermosiphonMinTempDiff) {
+                return true;
+            }
+            Real64 thermosiphonCapFrac = Curve::CurveValue(state, this->thermosiphonTempCurveIndex, dT);
+            Real64 capFrac = this->CyclingRatio;
+            if (thermosiphonCapFrac >= capFrac) {
+                this->thermosiphonStatus = 1;
+                this->Power = 0.0;
+                return false;
+            }
+            return true;
+        } else {
+            return true;
+        }
+    }
 
     EngineDrivenChillerSpecs *EngineDrivenChillerSpecs::factory(EnergyPlusData &state, std::string const &chillerName)
     {

src/EnergyPlus/PlantChillers.hh

@@ -214,6 +214,12 @@ namespace PlantChillers {
         Real64 HeatRecInletTemp; // (HeatRecOutletTemp is in base already)
         Real64 HeatRecMdot;
         Real64 ChillerCondAvgTemp; // the effective condenser temperature for chiller performance [C]
+        Real64 CyclingRatio = 0.0;
+
+        // thermosiphon model
+        int thermosiphonTempCurveIndex = 0;
+        Real64 thermosiphonMinTempDiff = 0.0;
+        int thermosiphonStatus = 0;
 
         // Default Constructor
         ElectricChillerSpecs()
@@ -260,12 +266,14 @@ namespace PlantChillers {
         );
 
         void oneTimeInit(EnergyPlusData &state) override;
+
+        bool thermosiphonDisabled(EnergyPlusData &state);
     };
 
     struct EngineDrivenChillerSpecs : BaseChillerSpecs
     {
         // temperature at the chiller evaporator side outlet
-        Constant::eFuel FuelType;
+        Constant::eFuel FuelType = Constant::eFuel::Invalid;
         Array1D<Real64> CapRatCoef;                // (EngineDriven RCAVC() ) coeff of cap ratio poly fit
         Array1D<Real64> PowerRatCoef;              // (EngineDriven ADJEC() ) coeff of power rat poly fit
         Array1D<Real64> FullLoadCoef;              // (EngineDriven RPWRC() ) coeff of full load poly. fit
@@ -363,7 +371,7 @@ namespace PlantChillers {
     struct GTChillerSpecs : BaseChillerSpecs
     {
         // Members
-        Constant::eFuel FuelType;
+        Constant::eFuel FuelType = Constant::eFuel::Invalid;
         Array1D<Real64> CapRatCoef;   // (GT RCAVC() ) coeff of cap ratio poly fit
         Array1D<Real64> PowerRatCoef; // (GT ADJEC() ) coeff of power rat poly fit
         Array1D<Real64> FullLoadCoef; // (GT RPWRC() ) coeff of full load poly. fit

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

@@ -2234,7 +2234,7 @@ void EIRPlantLoopHeatPump::oneTimeInit(EnergyPlusData &state)
                                 OutputProcessor::EndUseCat::Cooling,
                                 "Heat Pump");
             SetupOutputVariable(state,
-                                "Heat Pump Thermosiphon Status",
+                                "Thermosiphon Status",
                                 Constant::Units::None,
                                 this->thermosiphonStatus,
                                 OutputProcessor::TimeStepType::System,