Buildings.Fluid.Delays

Information

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.

Package Content

Name	Description
DelayFirstOrder	Delay element, approximated by a first order differential equation
Examples	Collection of models that illustrate model use and test models

Buildings.Fluid.Delays.DelayFirstOrder

Information

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.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V	V_nominal	Volume [m3]
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Nominal condition
Time	tau	60	Time constant at nominal flow [s]
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
ExtraProperty	C_nominal[Medium.nC]	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)
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
Assumptions
Boolean	allowFlowReversal	system.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
Boolean	prescribedHeatFlowRate	false	Set to true if the model has a prescribed heat flow at its heatPort

Connectors

Type	Name	Description
VesselFluidPorts_b	ports[nPorts]	Fluid inlets and outlets
HeatPort_a	heatPort	Heat 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";

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