Buildings.Fluid.Delays

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	V0	Volume [m3]
Ports
Boolean	use_portsData	false	= false to neglect pressure loss and kinetic energy
VesselPortsData	portsData[nPorts]		Data of inlet/outlet ports
Nominal condition
Time	tau	60	Time constant at nominal flow [s]
MassFlowRate	m_flow_nominal		Mass flow rate [kg/s]
Assumptions
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
replaceable model HeatTransfer		IdealHeatTransfer	Wall heat transfer
Initialization
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
Advanced
Port properties
MassFlowRate	m_flow_small	system.m_flow_small	Regularization range at zero mass flow rate [kg/s]

Connectors

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

Modelica definition

model DelayFirstOrder 
  "Delay element, approximated by a first order differential equation"
  extends Buildings.Fluid.MixingVolumes.MixingVolume(final V=V0, nPorts=2);

  parameter Modelica.SIunits.Time tau = 60 "Time constant at nominal flow";
  parameter Modelica.SIunits.MassFlowRate m_flow_nominal(min=0) 
    "Mass flow rate";

protected 
   parameter Medium.ThermodynamicState sta0 = Medium.setState_pTX(T=T_start,
         p=p_start, X=X_start[1:Medium.nXi]);
   parameter Modelica.SIunits.Density rho_nominal=Medium.density(sta0) 
    "Density, used to compute fluid volume";
   parameter Modelica.SIunits.Volume V0 = m_flow_nominal*tau/rho_nominal 
    "Volume of delay element";
end DelayFirstOrder;