Description: "Package with boiler models"

- Home > Modelica

## Buildings.Fluid.Boilers

Package with boiler models

### Information

This package contains components models for boilers.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

### Package Content

Name | Description
--- | ---
BoilerPolynomial | Boiler with efficiency curve described by a polynomial of the temperature
Examples | Collection of models that illustrate model use and test models

## Buildings.Fluid.Boilers.BoilerPolynomial

Boiler with efficiency curve described by a polynomial of the temperature

### Information

This is a model of a boiler whose efficiency is described by a polynomial. The heat input into the medium is

Q̇ = y Q̇0 η ⁄ η0

where y ∈ [0, 1] is the control signal, Q̇0 is the nominal power, η is the efficiency at the current operating point, and η0 is the efficiency at y=1 and nominal temperature T=T0 as specified by the parameter `T_nominal`.

The parameter `effCur` determines what polynomial is used to compute the efficiency, which is defined as

η = Q̇ ⁄ Q̇f,

where Q̇ is the heat transferred to the working fluid (typically water or air), and Q̇f is the heat of combustion released by the fuel.

The following polynomials can be selected to compute the efficiency:

Parameter `effCur` | Efficiency curve
--- | ---
Buildings.Fluid.Types.EfficiencyCurves.Constant | η = a1
Buildings.Fluid.Types.EfficiencyCurves.Polynomial | η = a1 + a2 y + a3 y2 + ...
Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear | η = a1 + a2 y + a3 y2 + (a4 + a5 y + a6 y2) T

where T is the boiler outlet temperature in Kelvin. For `effCur = Buildings.Fluid.Types.EfficiencyCurves.Polynomial`, an arbitrary number of polynomial coefficients can be specified.

The parameter `Q_flow_nominal` is the power transferred to the fluid for `y=1` and, if the efficiency depends on temperature, for `T=T0`.

The fuel mass flow rate and volume flow rate are computed as

ṁf = Q̇f ⁄ hf

and

V̇f = ṁf ⁄ ρf,

where the fuel heating value hf and the fuel mass density ρf are obtained from the parameter `fue`. Note that if η is the efficiency relative to the lower heating value, then the fuel properties also need to be used for the lower heating value.

Optionally, the port `heatPort` can be connected to a heat port outside of this model to impose a boundary condition in order to model heat losses to the ambient. When using this `heatPort`, make sure that the efficiency curve `effCur` does not already account for this heat loss.

On the Assumptions tag, the model can be parameterized to compute a transient or steady-state response. The transient response of the boiler is computed using a first order differential equation to compute the boiler's water and metal temperature, which are lumped into one state. The boiler outlet temperature is equal to this water temperature.

Extends from Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Power | Q_flow_nominal |  | Nominal heating power [W]
Temperature | T_nominal | 353.15 | 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]
Pressure | dp_nominal |  | Pressure difference [Pa]
Initialization
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Boolean | homotopyInitialization | true | = true, use homotopy method
Diagnostics
Boolean | show_T | true | = true, if actual temperature at port is computed
Flow resistance
Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time | tau | VWat*rho_default/m_flow_nomi... | Time constant at nominal flow (if energyDynamics <> SteadyState) [s]
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance
Dynamics | massDynamics | energyDynamics | Formulation of mass balance
Volume | VWat | 1.5E-6*Q_flow_nominal | Water 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.p_default | Start value of pressure [Pa]
Temperature | T_start | Medium.T_default | Start value of temperature [K]
MassFraction | X_start[Medium.nX] | Medium.X_default | Start value of mass fractions m_i/m [kg/kg]
ExtraProperty | C_start[Medium.nC] | fill(0, Medium.nC) | Start value of trace substances

### Connectors

Type | Name | Description
--- | --- | ---
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)
input RealInput | y | Part load ratio
HeatPort_a | heatPort | Heat port, can be used to connect to ambient
output RealOutput | T | [K]

### Modelica definition

model BoilerPolynomial "Boiler with efficiency curve described by a polynomial of the temperature" extends Interfaces.TwoPortHeatMassExchanger( redeclare final Buildings.Fluid.MixingVolumes.MixingVolume vol, show_T = true, final tau=VWat*rho_default/m_flow_nominal); parameter Modelica.SIunits.Power Q_flow_nominal "Nominal heating power"; parameter Modelica.SIunits.Temperature T_nominal = 353.15 "Temperature used to compute nominal efficiency (only used if efficiency curve depends on temperature)"; // Assumptions 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.SIunits.ThermalConductance UA=0.05*Q_flow_nominal/30 "Overall UA value"; parameter Modelica.SIunits.Volume VWat = 1.5E-6*Q_flow_nominal "Water volume of boiler"; parameter Modelica.SIunits.Mass mDry = 1.5E-3*Q_flow_nominal "Mass of boiler that will be lumped to water heat capacity"; Real eta(min=0) "Boiler efficiency"; Modelica.SIunits.Power QFue_flow "Heat released by fuel"; Modelica.SIunits.Power QWat_flow "Heat transfer from gas into water"; Modelica.SIunits.MassFlowRate mFue_flow "Fuel mass flow rate"; Modelica.SIunits.VolumeFlowRate VFue_flow "Fuel volume flow rate"; Modelica.Blocks.Interfaces.RealInput y(min=0, max=1) "Part load ratio"; protected Real eta_nominal "Boiler efficiency at nominal condition"; Modelica.Thermal.HeatTransfer.Components.ThermalConductor UAOve(G=UA) "Overall thermal conductance (if heatPort is connected)"; public Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort "Heat port, can be used to connect to ambient"; Modelica.Thermal.HeatTransfer.Components.HeatCapacitor heaCapDry(C=500*mDry, T(start=T_start)) if not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) "heat capacity of boiler metal"; Modelica.Blocks.Interfaces.RealOutput T(final quantity="ThermodynamicTemperature", final unit = "K", displayUnit = "degC", min=0); protected Buildings.HeatTransfer.Sources.PrescribedHeatFlow preHeaFlo; Modelica.Blocks.Sources.RealExpression Q_flow_in(y=QWat_flow); Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensor temSen "Temperature of fluid"; equation if effCur ==Buildings.Fluid.Types.EfficiencyCurves.Constant then eta = a[1]; eta_nominal = a[1]; elseif effCur ==Buildings.Fluid.Types.EfficiencyCurves.Polynomial then eta = Buildings.Utilities.Math.Functions.polynomial( a=a, x=y); eta_nominal = Buildings.Utilities.Math.Functions.polynomial( a=a, x=1); elseif effCur ==Buildings.Fluid.Types.EfficiencyCurves.QuadraticLinear then eta = Buildings.Utilities.Math.Functions.quadraticLinear( a=a, x1=y, x2=T); eta_nominal = Buildings.Utilities.Math.Functions.quadraticLinear( a=a, x1=1, x2=T_nominal); else eta = 0; eta_nominal = 999; end if; assert(eta > 0.001, "Efficiency curve is wrong."); // Heat released by fuel QFue_flow = y * Q_flow_nominal/eta_nominal; // Heat input into water QWat_flow = eta * QFue_flow; // Fuel mass flow rate and volume flow rate mFue_flow = QFue_flow/fue.h; VFue_flow = mFue_flow/fue.d; connect(UAOve.port_b, vol.heatPort); connect(UAOve.port_a, heatPort); connect(heaCapDry.port, vol.heatPort); connect(temSen.T, T); connect(preHeaFlo.port, vol.heatPort); connect(Q_flow_in.y,preHeaFlo. Q_flow); connect(vol.heatPort, temSen.port); end BoilerPolynomial;