modelBoilerPolynomial

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

Extends from Buildings.BaseClasses.BaseIconLow, Buildings.DHC.BaseClasses.Steam.PartialTwoPortTwoMedium.

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.DHC.BaseClasses.Steam.PartialTwoPortTwoMedium interface model. The saturated mixing volume for an evaporation process Buildings.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

Parameters

Type	Name	Default	Description
Modelica.Units.SI.Power	Q_flow_nominal		Nominal heating power
Modelica.Units.SI.Temperature	T_nominal	373.15	Temperature used to compute nominal efficiency (only used if efficiency curve depends on temperature)
Buildings.Fluid.Types.EfficiencyCurves	effCur	Buildings.Fluid.Types.EfficiencyCurves.Constant	Curve used to compute the efficiency
Real[:]	a	{0.9}	Coefficients for efficiency curve
Buildings.Fluid.Data.Fuels.Generic	fue		Fuel type
Modelica.Units.SI.ThermalConductance	UA	0.05*Q_flow_nominal/30	Overall UA value
Initialization
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 condition
Modelica.Units.SI.PressureDifference	dp_nominal		Pressure drop at nominal mass flow rate
Dynamics
Modelica.Units.SI.Volume	V	1.5E-6*Q_flow_nominal	Total internal volume of boiler
Modelica.Units.SI.Mass	mDry	1.5E-3*Q_flow_nominal	Mass of boiler that will be lumped to water heat capacity

Components

Type	Name	Default	Description
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		Part load ratio
Modelica.Blocks.Interfaces.RealOutput	VLiq		Output liquid water volume
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	heatPort		Heat port, can be used to connect to ambient
Modelica.Thermal.HeatTransfer.Components.HeatCapacitor	heaCapDry		Heat capacity of boiler metal
Buildings.DHC.Plants.Steam.BaseClasses.ControlVolumeEvaporation	vol		Steam/water control volume
Buildings.Fluid.FixedResistances.PressureDrop	res		Flow resistance
Modelica.Blocks.Interfaces.RealOutput	QFueFlo		Heat flow rate of the fuel

Name	Description
MediumWat	Water medium - port_a (inlet)
MediumSte	Steam medium - port_b (oulet)

Revisions

September 15, 2023, by Kathryn Hinkelman:
Updated publication references.
February 25, 2022 by Kathryn Hinkelman:
Refactored base classes for improved extensibility and relocated models into Steam subpackages.
July 22, 2021 by Kathryn Hinkelman:
First implementation.