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.
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_ain liquid state and exitsport_bin 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:
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.
Reference
Hinkelman, Kathryn, Saranya Anbarasu, Michael Wetter, Antoine Gautier, and Wangda Zuo. 2022. “A Fast and Accurate Modeling Approach for Water and Steam Thermodynamics with Practical Applications in District Heating System Simulation.” Preprint. February 24. doi:10.13140/RG.2.2.20710.29762.
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
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.
Reference
Hinkelman, Kathryn, Saranya Anbarasu, Michael Wetter, Antoine Gautier, and Wangda Zuo. 2022. “A Fast and Accurate Modeling Approach for Water and Steam Thermodynamics with Practical Applications in District Heating System Simulation.” Preprint. February 24. doi:10.13140/RG.2.2.20710.29762.
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;