Buildings.Experimental.DHC.Plants.Steam.BaseClasses

Package with base classes for Buildings.Experimental.DHC.Plants.Steam

Information

This package contains base classes that are used to construct the models in Buildings.Experimental.DHC.Plants.Steam.

Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).

Package Content

Name	Description
BoilerPolynomial	A equilibrium boiler with water phase change from liquid to vapor, discharging saturated steam vapor, with the efficiency curve described by a polynomial.
ControlVolumeEvaporation	Control volume model exhibiting the evaporation process of water
Examples	Collection of models that illustrate model use and test models

Buildings.Experimental.DHC.Plants.Steam.BaseClasses.BoilerPolynomial

A equilibrium boiler with water phase change from liquid to vapor, discharging saturated steam vapor, with the efficiency curve described by a polynomial.

Buildings.Experimental.DHC.Plants.Steam.BaseClasses.BoilerPolynomial

Information

This model represents a steam boiler that discharges saturated steam and has an efficiency curve defined by a polynomial. The efficiency in this model represents the fuel-to-water efficiency (e.g., thermal efficiency). This model is similar to the Buildings.Fluid.Boilers.BoilerPolynomial for the efficiency and fuel mass flow rate computation with the following exceptions:

Water enters port_a in liquid state and exits port_b in vapor state.
The liquid and vapor phases are at equilibrium; thus, the steam boiler is constrained to saturated states only with the volume containing a wet steam mixture.
If the boiler is configured in steady state, several blocks involving the heat flow rate are conditionally removed to avoid overconstraining the model. This is because the discharging fluid is constrained at a saturated state. The blocks that are conditionally removed as a result are within the green region in the below figure:

Boiler polynomial steam with blocks in green conditionally removed if steady state

Implementation

In order to improve the numerical efficiency, this model follows the split-medium approach using the Buildings.Experimental.DHC.BaseClasses.Steam.PartialTwoPortTwoMedium interface model. The saturated mixing volume for an evaporation process Buildings.Experimental.DHC.Plants.Steam.BaseClasses.ControlVolumeEvaporation represents the phase change process of water from liquid to vapor at equilibrium.

References

Kathryn Hinkelman, Saranya Anbarasu, Michael Wetter, Antoine Gautier, Wangda Zuo. 2022. “A Fast and Accurate Modeling Approach for Water and Steam Thermodynamics with Practical Applications in District Heating System Simulation,” Energy, 254(A), pp. 124227. 10.1016/j.energy.2022.124227

Kathryn Hinkelman, Saranya Anbarasu, Michael Wetter, Antoine Gautier, Baptiste Ravache, Wangda Zuo 2022. “Towards Open-Source Modelica Models For Steam-Based District Heating Systems.” Proc. of the 1st International Workshop On Open Source Modelling And Simulation Of Energy Systems (OSMSES 2022), Aachen, German, April 4-5, 2022. 10.1109/OSMSES54027.2022.9769121

Extends from Buildings.BaseClasses.BaseIconLow (Base icon with model name below the icon), Buildings.Experimental.DHC.BaseClasses.Steam.PartialTwoPortTwoMedium (Partial model with two ports with two separate medium models without storing mass or energy).

Parameters

Type	Name	Default	Description
replaceable package Medium_a		PartialMedium	Medium model for port_a (inlet)
replaceable package Medium_b		PartialMedium	Medium model for port_b (outlet)
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
replaceable package MediumWat		Buildings.Media.Specialized....	Water medium - port_a (inlet)
replaceable package MediumSte		Buildings.Media.Steam	Steam medium - port_b (oulet)
Power	Q_flow_nominal		Nominal heating power [W]
Temperature	T_nominal	373.15	Temperature used to compute nominal efficiency (only used if efficiency curve depends on temperature) [K]
EfficiencyCurves	effCur	Buildings.Fluid.Types.Effici...	Curve used to compute the efficiency
Real	a[:]	{0.9}	Coefficients for efficiency curve
Generic	fue		Fuel type
ThermalConductance	UA	0.05*Q_flow_nominal/30	Overall UA value [W/K]
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
PressureDifference	dp_nominal		Pressure drop at nominal mass flow rate [Pa]
Advanced
Diagnostics
Boolean	show_T	false	= true, if actual temperature at port is computed
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal. Used only if model has two ports.
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Type of energy balance: dynamic (3 initialization options) or steady state
Dynamics	massDynamics	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state
Volume	V	1.5E-6*Q_flow_nominal	Total internal volume of boiler [m3]
Mass	mDry	1.5E-3*Q_flow_nominal	Mass of boiler that will be lumped to water heat capacity [kg]
Initialization
AbsolutePressure	p_start	Medium_b.p_default	Start value of pressure [Pa]
Temperature	T_start	MediumSte.saturationTemperat...	Start value of temperature [K]
Boolean	fixed_p_start	false	Set to true if p_start is to be used as an explicit initial equation, not an initial guess

Connectors

Type	Name	Description
replaceable package Medium_a		Medium model for port_a (inlet)
replaceable package Medium_b		Medium model for port_b (outlet)
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)
replaceable package MediumWat		Water medium - port_a (inlet)
replaceable package MediumSte		Steam medium - port_b (oulet)
input RealInput	y	Part load ratio
output RealOutput	VLiq	Output liquid water volume [m3]
HeatPort_a	heatPort	Heat port, can be used to connect to ambient
output RealOutput	QFueFlo	Heat flow rate of the fuel [W]

Modelica definition

model BoilerPolynomial "A equilibrium boiler with water phase change from liquid to vapor, discharging saturated steam vapor, with the efficiency curve described by a polynomial." extends Buildings.BaseClasses.BaseIconLow; extends Buildings.Experimental.DHC.BaseClasses.Steam.PartialTwoPortTwoMedium( redeclare final package Medium_a=MediumWat, redeclare final package Medium_b=MediumSte, final T_start=MediumSte.saturationTemperature(p_start)); // Medium declarations replaceable package MediumWat = Buildings.Media.Specialized.Water.TemperatureDependentDensity "Water medium - port_a (inlet)"; replaceable package MediumSte = Buildings.Media.Steam "Steam medium - port_b (oulet)"; // Initialization parameter Boolean fixed_p_start=false "Set to true if p_start is to be used as an explicit initial equation, not an initial guess"; // Nominal conditions parameter Modelica.Units.SI.PressureDifference dp_nominal(displayUnit="Pa") "Pressure drop at nominal mass flow rate"; parameter Modelica.Units.SI.Power Q_flow_nominal "Nominal heating power"; parameter Modelica.Units.SI.Temperature T_nominal = 373.15 "Temperature used to compute nominal efficiency (only used if efficiency curve depends on temperature)"; // Efficiency, fuel, and boiler properties parameter Buildings.Fluid.Types.EfficiencyCurves effCur= Buildings.Fluid.Types.EfficiencyCurves.Constant "Curve used to compute the efficiency"; parameter Real a[:] = {0.9} "Coefficients for efficiency curve"; parameter Buildings.Fluid.Data.Fuels.Generic fue "Fuel type"; parameter Modelica.Units.SI.ThermalConductance UA=0.05*Q_flow_nominal/30 "Overall UA value"; parameter Modelica.Units.SI.Volume V = 1.5E-6*Q_flow_nominal "Total internal volume of boiler"; parameter Modelica.Units.SI.Mass mDry = 1.5E-3*Q_flow_nominal "Mass of boiler that will be lumped to water heat capacity"; // Variables Modelica.Units.SI.Efficiency eta= if effCur == Buildings.Fluid.Types.EfficiencyCurves.Constant then a[1] elseif effCur == Buildings.Fluid.Types.EfficiencyCurves.Polynomial then Buildings.Utilities.Math.Functions.polynomial(a=a, x=y_internal) elseif effCur == Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear then Buildings.Utilities.Math.Functions.quadraticLinear( a=aQuaLin, x1=y_internal, x2=MediumSte.saturationTemperature(port_a.p)) else 0 "Boiler efficiency"; Modelica.Units.SI.Power QFue_flow = y_internal * Q_flow_nominal/eta_nominal "Heat released by fuel"; Modelica.Units.SI.Power QWat_flow = eta * QFue_flow "Heat transfer from gas into water"; Modelica.Units.SI.MassFlowRate mFue_flow = QFue_flow/fue.h "Fuel mass flow rate"; Modelica.Units.SI.VolumeFlowRate VFue_flow = mFue_flow/fue.d "Fuel volume flow rate"; Modelica.Blocks.Interfaces.RealInput y(min=0, max=1) if not steadyDynamics "Part load ratio"; Modelica.Blocks.Interfaces.RealOutput VLiq( final quantity="Volume", final unit="m3", min=0) "Output liquid water volume"; Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort if not steadyDynamics "Heat port, can be used to connect to ambient"; Modelica.Thermal.HeatTransfer.Components.HeatCapacitor heaCapDry( C=500*mDry, T(start=T_start)) if not steadyDynamics "Heat capacity of boiler metal"; Buildings.Experimental.DHC.Plants.Steam.BaseClasses.ControlVolumeEvaporation vol( redeclare final package MediumSte = MediumSte, redeclare final package MediumWat = MediumWat, final allowFlowReversal=allowFlowReversal, final energyDynamics=energyDynamics, final massDynamics=massDynamics, final p_start=p_start, final m_flow_nominal=m_flow_nominal, final show_T=show_T, final V=V, final fixed_p_start=fixed_p_start) "Steam/water control volume"; Buildings.Fluid.FixedResistances.PressureDrop res( redeclare final package Medium = MediumWat, final allowFlowReversal=allowFlowReversal, final m_flow_nominal=m_flow_nominal, final show_T=show_T, final dp_nominal=dp_nominal) "Flow resistance"; Modelica.Blocks.Interfaces.RealOutput QFueFlo( final quantity="HeatFlowRate", final unit="W", min=0) "Heat flow rate of the fuel"; protected final parameter Boolean steadyDynamics= if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then true else false "= true, if steady state formulation"; parameter Real eta_nominal(fixed=false) "Boiler efficiency at nominal condition"; parameter Real aQuaLin[6] = if size(a, 1) == 6 then a else fill(0, 6) "Auxiliary variable for efficiency curve because quadraticLinear requires exactly 6 elements"; Modelica.Blocks.Interfaces.RealInput y_internal(min=0, max=1) "Internal block needed for conditional input part load ratio"; Buildings.HeatTransfer.Sources.PrescribedHeatFlow preHeaFlo if not steadyDynamics "Prescribed heat flow (if heatPort is connected)"; Modelica.Blocks.Sources.RealExpression Q_flow_in(y=QWat_flow) if not steadyDynamics "Heat transfer from gas into water (if heatPort is connected)"; Modelica.Thermal.HeatTransfer.Components.ThermalConductor UAOve(G=UA) if not steadyDynamics "Overall thermal conductance (if heatPort is connected)"; Modelica.Blocks.Sources.RealExpression QFue_flow_out(y=QFue_flow) "Heat flow rate of the fuel"; initial equation if effCur == Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear then assert(size(a, 1) == 6, "The boiler has the efficiency curve set to 'Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear', and hence the parameter 'a' must have exactly 6 elements. However, only " + String(size(a, 1)) + " elements were provided."); end if; if effCur == Buildings.Fluid.Types.EfficiencyCurves.Constant then eta_nominal = a[1]; elseif effCur == Buildings.Fluid.Types.EfficiencyCurves.Polynomial then eta_nominal = Buildings.Utilities.Math.Functions.polynomial( a=a, x=1); elseif effCur == Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear then // For this efficiency curve, a must have 6 elements. eta_nominal = Buildings.Utilities.Math.Functions.quadraticLinear( a=aQuaLin, x1=1, x2=T_nominal); else eta_nominal = 999; end if; equation assert(eta > 0.001, "Efficiency curve is wrong."); connect(y,y_internal); if steadyDynamics then if allowFlowReversal then -QWat_flow = port_a.m_flow*actualStream(port_a.h_outflow) + port_b.m_flow*actualStream(port_b.h_outflow); else -QWat_flow = port_a.m_flow*inStream(port_a.h_outflow) + port_b.m_flow*port_b.h_outflow; end if; end if; connect(UAOve.port_a, heatPort); connect(Q_flow_in.y,preHeaFlo. Q_flow); connect(heaCapDry.port, UAOve.port_b); connect(preHeaFlo.port, UAOve.port_b); connect(vol.heatPort, UAOve.port_b); connect(vol.port_b, port_b); connect(port_a, res.port_a); connect(res.port_b, vol.port_a); connect(vol.VLiq,VLiq); connect(QFue_flow_out.y, QFueFlo); end BoilerPolynomial;

Buildings.Experimental.DHC.Plants.Steam.BaseClasses.ControlVolumeEvaporation

Control volume model exhibiting the evaporation process of water

Buildings.Experimental.DHC.Plants.Steam.BaseClasses.ControlVolumeEvaporation

Information

This model represents an evaporation process of water with liquid and vapor phases in equilibrium and at a saturated state. Further information regarding the model formulation and assumptions are in the base class Buildings.Experimental.DHC.BaseClasses.Steam.PartialSaturatedControlVolume.

References

Extends from Buildings.Experimental.DHC.BaseClasses.Steam.PartialSaturatedControlVolume (Partial control volume for evaporation/condensation processes).

Parameters

Type	Name	Default	Description
replaceable package Medium_a		PartialMedium	Medium model for port_a (inlet)
replaceable package Medium_b		PartialMedium	Medium model for port_b (outlet)
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
replaceable package MediumWat		TemperatureDependentDensity	Liquid water medium
replaceable package MediumSte		Steam	Steam medium
Volume	V		Total volume [m3]
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Initialization
AbsolutePressure	p.start	p_start	Pressure inside volume [Pa]
VolumeFlowRate	VWat_flow.start	0	Volumetric flow rate of liquid water [m3/s]
SpecificEnthalpy	hSte.start	MediumSte.h_default	Specific enthalpy of steam vapor [J/kg]
SpecificEnthalpy	hWat.start	MediumWat.h_default	Specific enthalpy of liquid water [J/kg]
Advanced
Diagnostics
Boolean	show_T	false	= true, if actual temperature at port is computed
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal. Used only if model has two ports.
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Type of energy balance: dynamic (3 initialization options) or steady state
Dynamics	massDynamics	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state
Initialization
AbsolutePressure	p_start	MediumSte.p_default	Start value of pressure [Pa]
Volume	VWat_start	V/2	Start value of liquid volume [m3]
Boolean	fixed_p_start	false	Set to true if p_start is to be used as an explicit initial equation, not an initial guess

Connectors

Type	Name	Description
replaceable package Medium_a		Medium model for port_a (inlet)
replaceable package Medium_b		Medium model for port_b (outlet)
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)
HeatPort_a	heatPort	Heat port
output RealOutput	VLiq	Liquid volume [m3]

Modelica definition

model ControlVolumeEvaporation "Control volume model exhibiting the evaporation process of water" extends Buildings.Experimental.DHC.BaseClasses.Steam.PartialSaturatedControlVolume ( redeclare final package Medium_a=MediumWat, redeclare final package Medium_b=MediumSte, hSte(start = MediumSte.h_default), hWat(start = MediumWat.h_default), p(final fixed=fixed_p_start)); parameter Boolean fixed_p_start = false "Set to true if p_start is to be used as an explicit initial equation, not an initial guess"; equation // boundary conditions at the ports port_a.m_flow = mWat_flow; port_a.h_outflow = hWat; port_b.m_flow = mSte_flow; port_b.h_outflow = hSte; end ControlVolumeEvaporation;