Buildings.Fluid.Boilers

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

Information

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.

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.

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
TemperatureDifference	dT_nominal		Temperature difference of water loop at nominal load [K]
ThermalConductance	UA	0.05*Q_flow_nominal/30	Overall UA value [W/K]
Nominal condition
MassFlowRate	m_flow_nominal	Q_flow_nominal/dT_nominal/cp...	Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Time	tau	0	Time constant at nominal flow [s]
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	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Dynamics
Dynamics	energyDynamics	system.energyDynamics	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]
Advanced
MassFlowRate	m_flow_small	1E-4*m_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	true	= true, if volume flow rate at inflowing port is computed
Initialization
AbsolutePressure	p_a_start	system.p_start	Guess value for inlet pressure [Pa]
AbsolutePressure	p_b_start	p_a_start	Guess value for outlet pressure [Pa]
AbsolutePressure	p_start	system.p_start	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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
Flow resistance
Boolean	from_dp	true	= 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

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"
  // For the preDro(m_flow(nominal)), we use a constant specific heat capacity.
  // Otherwise, the nominal attribute won't be set by Dymola 7.1 because
  // cp_nominal is a non-literal value.
  // Since only the order of magnitude should be correct, using a constant
  // value for cp suffices.
  extends Interfaces.PartialDynamicTwoPortTransformer(
    m_flow_nominal=Q_flow_nominal/dT_nominal/cp_nominal, final tau=0,
    preDro(m_flow(nominal=Q_flow_nominal/dT_nominal/4200)),
    vol(final V =   VWat));

  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 Modelica.SIunits.TemperatureDifference dT_nominal(min=0) 
    "Temperature difference of water loop at nominal load";
  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 if 
        not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) 
    "Mass of boiler that will be lumped to water heat capacity";

  Real eta(min=0) "Boiler efficiency";

  Modelica.SIunits.Power QFue_flow "Sensible heat released by fuel";
  Modelica.SIunits.Power QWat_flow "Heat transfer from gas into water";

  Modelica.Blocks.Interfaces.RealInput y(min=0, max=1) "Part load ratio";
protected 
  Real eta_nominal "Boiler efficiency at nominal condition";

  parameter Modelica.SIunits.SpecificHeatCapacity cp_nominal=
      Medium.specificHeatCapacityCp(sta_nominal) 
    "Specific heat capacity of fluid in boiler";
protected 
  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);
public 
  Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow preHeaFlo;
  Modelica.Blocks.Sources.RealExpression Q_flow_in(y=QWat_flow);
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;
  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);
end BoilerPolynomial;