Description: "Package with delay models"

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## Buildings.Fluid.Delays

Package with delay models

### 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.

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

### 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... | Formulation of energy balance
Dynamics | massDynamics | energyDynamics | Formulation of mass balance
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
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 | = 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 for sensible heat input

### 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;