Buildings.Fluid.Delays

Package with delay models

Information

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

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

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

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

Delay element, approximated by a first order differential equation

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.

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

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...	Type of energy balance: dynamic (3 initialization options) or steady state
Dynamics	massDynamics	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state
Real	mSenFac	1	Factor for scaling the sensible thermal mass of the volume
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
Boolean	use_C_flow	false	Set to true to enable input connector for trace substance
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal. Used only if model has two ports.

Connectors

Type	Name	Description
VesselFluidPorts_b	ports[nPorts]	Fluid inlets and outlets
HeatPort_a	heatPort	Heat port for sensible heat input
output RealOutput	U	Internal energy of the component [J]
output RealOutput	m	Mass of the component [kg]
output RealOutput	mXi[Medium.nXi]	Species mass of the component [kg]
output RealOutput	mC[Medium.nC]	Trace substance mass of the component [kg]
input RealInput	C_flow[Medium.nC]	Trace substance mass flow rate added to the medium

Modelica definition

model DelayFirstOrder "Delay element, approximated by a first order differential equation" extends Buildings.Fluid.MixingVolumes.MixingVolume(final V=V_nominal, final mSenFac=1); 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;