LBL logo


Package with delay models


This package contains components models for transport delays in piping networks.

The model Buildings.Fluid.Delays.DelayFirstOrder approximates transport delays using a first order differential equation.

For a discretized model of a pipe or duct, see Buildings.Fluid.FixedResistances.Pipe.

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

Package Content

Buildings.Fluid.Delays.DelayFirstOrder DelayFirstOrder Delay element, approximated by a first order differential equation
Buildings.Fluid.Delays.Examples Examples Collection of models that illustrate model use and test models

Buildings.Fluid.Delays.DelayFirstOrder Buildings.Fluid.Delays.DelayFirstOrder

Delay element, approximated by a first order differential equation



This model approximates a transport delay using a first order differential equations.

The model consists of a mixing volume with two ports. The size of the mixing volume is such that at the nominal mass flow rate m_flow_nominal, the time constant of the volume is equal to the parameter tau.

The heat flux connector is optional, it need not be connnected.

Extends from Buildings.Fluid.MixingVolumes.MixingVolume (Mixing volume with inlet and outlet ports (flow reversal is allowed)).


replaceable package MediumPartialMediumMedium in the component
VolumeVV_nominalVolume [m3]
Nominal condition
MassFlowRatem_flow_nominal Nominal mass flow rate [kg/s]
DynamicsenergyDynamicsModelica.Fluid.Types.Dynamic...Formulation of energy balance
DynamicsmassDynamicsenergyDynamicsFormulation of mass balance
Nominal condition
Timetau60Time constant at nominal flow [s]
AbsolutePressurep_startMedium.p_defaultStart value of pressure [Pa]
TemperatureT_startMedium.T_defaultStart value of temperature [K]
MassFractionX_start[Medium.nX]Medium.X_defaultStart value of mass fractions m_i/m [kg/kg]
ExtraPropertyC_start[Medium.nC]fill(0, Medium.nC)Start value of trace substances
ExtraPropertyC_nominal[Medium.nC]fill(1E-2, Medium.nC)Nominal value of trace substances. (Set to typical order of magnitude.)
MassFlowRatem_flow_small1E-4*abs(m_flow_nominal)Small mass flow rate for regularization of zero flow [kg/s]
BooleanhomotopyInitializationtrue= true, use homotopy method
BooleanallowFlowReversalsystem.allowFlowReversal= true to allow flow reversal in medium, false restricts to design direction (ports[1] -> ports[2]). Used only if model has two ports.
Heat transfer
BooleanprescribedHeatFlowRatefalseSet to true if the model has a prescribed heat flow at its heatPort


VesselFluidPorts_bports[nPorts]Fluid inlets and outlets
HeatPort_aheatPortHeat port connected to outflowing medium

Modelica definition

model DelayFirstOrder 
  "Delay element, approximated by a first order differential equation"
  extends Buildings.Fluid.MixingVolumes.MixingVolume(final V=V_nominal);

  parameter Modelica.SIunits.Time tau = 60 "Time constant at nominal flow";

   parameter Modelica.SIunits.Volume V_nominal = m_flow_nominal*tau/rho_default 
    "Volume of delay element";
end DelayFirstOrder;

Automatically generated Thu Oct 24 15:08:27 2013.