Description: "Package with interfaces for fluid models"

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## Buildings.Fluid.Interfaces

Package with interfaces for fluid models

### Information

This package contains basic classes that are used to build component models that change the state of the fluid. The classes are not directly usable, but can be extended when building a new model.

Extends from Modelica.Icons.InterfacesPackage (Icon for packages containing interfaces).

### Package Content

Name | Description
--- | ---
UsersGuide | User's Guide
ConservationEquation | Lumped volume with mass and energy balance
FourPort | Partial model with four ports
FourPortHeatMassExchanger | Model transporting two fluid streams between four ports with storing mass or energy
PartialFourPortInterface | Partial model transporting fluid between two ports without storing mass or energy
PartialTwoPort | Partial component with two ports
PartialTwoPortInterface | Partial model transporting fluid between two ports without storing mass or energy
PartialTwoPortTransport | Partial element transporting fluid between two ports without storage of mass or energy
PrescribedOutletState | Component that assigns the outlet fluid property at port_a based on an input signal
StaticFourPortHeatMassExchanger | Partial model transporting two fluid streams between four ports without storing mass or energy
StaticTwoPortConservationEquation | Partial model for static energy and mass conservation equations
StaticTwoPortHeatMassExchanger | Partial model transporting fluid between two ports without storing mass or energy
TwoPortHeatMassExchanger | Partial model transporting one fluid stream with storing mass or energy
FourPortFlowResistanceParameters | Parameters for flow resistance for models with four ports
LumpedVolumeDeclarations | Declarations for lumped volumes
PrescribedOutletStateParameters | Parameters for models with prescribed outlet state
TwoPortFlowResistanceParameters | Parameters for flow resistance for models with two ports
Examples | Collection of models that illustrate model use and test models

## Buildings.Fluid.Interfaces.ConservationEquation

Lumped volume with mass and energy balance

### Information

Basic model for an ideally mixed fluid volume with the ability to store mass and energy. It implements a dynamic or a steady-state conservation equation for energy and mass fractions. The model has zero pressure drop between its ports.

#### Implementation

When extending or instantiating this model, the input `fluidVolume`, which is the actual volume occupied by the fluid, needs to be assigned. For most components, this can be set to a parameter.

Input connectors of the model are

- `Q_flow`, which is the sensible plus latent heat flow rate added to the medium, and
- `mWat_flow`, which is the moisture mass flow rate added to the medium.

The model can be used as a dynamic model or as a steady-state model. However, for a steady-state model with exactly two fluid ports connected, the model Buildings.Fluid.Interfaces.StaticTwoPortConservationEquation provides a more efficient implementation.

For a model that instantiates this model, see Buildings.Fluid.MixingVolumes.MixingVolume.

Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Volume | fluidVolume |  | Volume [m3]
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
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.)

### Connectors

Type | Name | Description
--- | --- | ---
VesselFluidPorts_b | ports[nPorts] | Fluid inlets and outlets
input RealInput | Q_flow | Sensible plus latent heat flow rate transferred into the medium [W]
input RealInput | mWat_flow | Moisture mass flow rate added to the medium [kg/s]
output RealOutput | hOut | Leaving enthalpy of the component [J/kg]
output RealOutput | XiOut[Medium.nXi] | Leaving species concentration of the component [1]
output RealOutput | COut[Medium.nC] | Leaving trace substances of the component

### Modelica definition

model ConservationEquation "Lumped volume with mass and energy balance" extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations; constant Boolean initialize_p = not Medium.singleState "= true to set up initial equations for pressure"; // Port definitions parameter Integer nPorts=0 "Number of ports"; Modelica.Fluid.Vessels.BaseClasses.VesselFluidPorts_b ports[nPorts]( redeclare each final package Medium = Medium) "Fluid inlets and outlets"; // Set nominal attributes where literal values can be used. Medium.BaseProperties medium( preferredMediumStates= not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState), p(start=p_start, stateSelect=if not (massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) then StateSelect.prefer else StateSelect.default), h(start=hStart), T(start=T_start), Xi(start=X_start[1:Medium.nXi], each stateSelect=if (not (substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState)) then StateSelect.prefer else StateSelect.default), X(start=X_start), d(start=rho_nominal)) "Medium properties"; Modelica.SIunits.Energy U "Internal energy of fluid"; Modelica.SIunits.Mass m "Mass of fluid"; Modelica.SIunits.Mass[Medium.nXi] mXi "Masses of independent components in the fluid"; Modelica.SIunits.Mass[Medium.nC] mC "Masses of trace substances in the fluid"; // C need to be added here because unlike for Xi, which has medium.Xi, // there is no variable medium.C Medium.ExtraProperty C[Medium.nC](nominal=C_nominal) "Trace substance mixture content"; Modelica.SIunits.MassFlowRate mb_flow "Mass flows across boundaries"; Modelica.SIunits.MassFlowRate[Medium.nXi] mbXi_flow "Substance mass flows across boundaries"; Medium.ExtraPropertyFlowRate[Medium.nC] mbC_flow "Trace substance mass flows across boundaries"; Modelica.SIunits.EnthalpyFlowRate Hb_flow "Enthalpy flow across boundaries or energy source/sink"; // Inputs that need to be defined by an extending class parameter Modelica.SIunits.Volume fluidVolume "Volume"; final parameter Modelica.SIunits.HeatCapacity CSen= (mSenFac - 1)*rho_default*cp_default*fluidVolume "Aditional heat capacity for implementing mFactor"; Modelica.Blocks.Interfaces.RealInput Q_flow(unit="W") "Sensible plus latent heat flow rate transferred into the medium"; Modelica.Blocks.Interfaces.RealInput mWat_flow(unit="kg/s") "Moisture mass flow rate added to the medium"; // Outputs that are needed in models that extend this model Modelica.Blocks.Interfaces.RealOutput hOut(unit="J/kg", start=hStart) "Leaving enthalpy of the component"; Modelica.Blocks.Interfaces.RealOutput XiOut[Medium.nXi](each unit="1", each min=0, each max=1) "Leaving species concentration of the component"; Modelica.Blocks.Interfaces.RealOutput COut[Medium.nC](each min=0) "Leaving trace substances of the component"; protected Medium.EnthalpyFlowRate ports_H_flow[nPorts]; Modelica.SIunits.MassFlowRate ports_mXi_flow[nPorts,Medium.nXi]; Medium.ExtraPropertyFlowRate ports_mC_flow[nPorts,Medium.nC]; parameter Modelica.SIunits.SpecificHeatCapacity cp_default= Medium.specificHeatCapacityCp(state=state_default) "Heat capacity, to compute additional dry mass"; parameter Modelica.SIunits.Density rho_nominal=Medium.density( Medium.setState_pTX( T=T_start, p=p_start, X=X_start[1:Medium.nXi])) "Density, used to compute fluid mass"; // Parameter for avoiding extra overhead calculations when CSen==0 final parameter Boolean computeCSen = CSen > Modelica.Constants.eps; final parameter Medium.ThermodynamicState state_default = Medium.setState_pTX( T=Medium.T_default, p=Medium.p_default, X=Medium.X_default[1:Medium.nXi]) "Medium state at default values"; // Density at medium default values, used to compute the size of control volumes final parameter Modelica.SIunits.Density rho_default=Medium.density( state=state_default) "Density, used to compute fluid mass"; // Parameter that is used to construct the vector mXi_flow final parameter Real s[Medium.nXi] = {if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i], string2="Water", caseSensitive=false) then 1 else 0 for i in 1:Medium.nXi} "Vector with zero everywhere except where species is"; parameter Modelica.SIunits.SpecificEnthalpy hStart= Medium.specificEnthalpy_pTX(p_start, T_start, X_start) "Start value for specific enthalpy"; initial equation // Assert that the substance with name 'water' has been found. assert(Medium.nXi == 0 or abs(sum(s)-1) < 1e-5, "If Medium.nXi > 1, then substance 'water' must be present for one component.'" + Medium.mediumName + "'.\n" + "Check medium model."); // Make sure that if energyDynamics is SteadyState, then // massDynamics is also SteadyState. // Otherwise, the system of ordinary differential equations may be inconsistent. if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then assert(massDynamics == energyDynamics, " If 'massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState', then it is required that 'energyDynamics==Modelica.Fluid.Types.Dynamics.SteadyState'. Otherwise, the system of equations may not be consistent. You need to select other parameter values."); end if; // initialization of balances if energyDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then medium.T = T_start; else if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then der(medium.T) = 0; end if; end if; if massDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then if initialize_p then medium.p = p_start; end if; else if massDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then if initialize_p then der(medium.p) = 0; end if; end if; end if; if substanceDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then medium.Xi = X_start[1:Medium.nXi]; else if substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then der(medium.Xi) = zeros(Medium.nXi); end if; end if; if traceDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then C = C_start[1:Medium.nC]; else if traceDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then der(C) = zeros(Medium.nC); end if; end if; equation // Total quantities if massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then m = fluidVolume*rho_nominal; else m = fluidVolume*medium.d; end if; mXi = m*medium.Xi; if computeCSen then U = m*medium.u + CSen*(medium.T-Medium.reference_T); else U = m*medium.u; end if; mC = m*C; hOut = medium.h; XiOut = medium.Xi; COut = C; for i in 1:nPorts loop ports_H_flow[i] = ports[i].m_flow * actualStream(ports[i].h_outflow) "Enthalpy flow"; ports_mXi_flow[i,:] = ports[i].m_flow * actualStream(ports[i].Xi_outflow) "Component mass flow"; ports_mC_flow[i,:] = ports[i].m_flow * actualStream(ports[i].C_outflow) "Trace substance mass flow"; end for; for i in 1:Medium.nXi loop mbXi_flow[i] = sum(ports_mXi_flow[:,i]); end for; for i in 1:Medium.nC loop mbC_flow[i] = sum(ports_mC_flow[:,i]); end for; mb_flow = sum(ports.m_flow); Hb_flow = sum(ports_H_flow); // Energy and mass balances if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then 0 = Hb_flow + Q_flow; else der(U) = Hb_flow + Q_flow; end if; if massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then 0 = mb_flow + mWat_flow; else der(m) = mb_flow + mWat_flow; end if; if substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then zeros(Medium.nXi) = mbXi_flow + mWat_flow * s; else der(mXi) = mbXi_flow + mWat_flow * s; end if; if traceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then zeros(Medium.nC) = mbC_flow; else der(mC) = mbC_flow; end if; // Properties of outgoing flows for i in 1:nPorts loop ports[i].p = medium.p; ports[i].h_outflow = medium.h; ports[i].Xi_outflow = medium.Xi; ports[i].C_outflow = C; end for; end ConservationEquation;

## Buildings.Fluid.Interfaces.FourPort

Partial model with four ports

### Information

This model defines an interface for components with four ports. The parameters `allowFlowReversal1` and `allowFlowReversal2` may be used by models that extend this model to treat flow reversal.

This model is identical to Modelica.Fluid.Interfaces.PartialTwoPort, except that it has four ports.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium1 | Modelica.Media.Interfaces.Pa... | Medium 1 in the component
replaceable package Medium2 | Modelica.Media.Interfaces.Pa... | Medium 2 in the component
Assumptions
Boolean | allowFlowReversal1 | true | = true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean | allowFlowReversal2 | true | = true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy | h_outflow_a1_start | Medium1.h_default | Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy | h_outflow_b1_start | Medium1.h_default | Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy | h_outflow_a2_start | Medium2.h_default | Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy | h_outflow_b2_start | Medium2.h_default | Start value for enthalpy flowing out of port b2 [J/kg]

### Connectors

Type | Name | Description
--- | --- | ---
replaceable package Medium1 | Medium 1 in the component
replaceable package Medium2 | Medium 2 in the component
FluidPort_a | port_a1 | Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b | port_b1 | Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a | port_a2 | Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b | port_b2 | Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

### Modelica definition

model FourPort "Partial model with four ports" replaceable package Medium1 = Modelica.Media.Interfaces.PartialMedium "Medium 1 in the component"; replaceable package Medium2 = Modelica.Media.Interfaces.PartialMedium "Medium 2 in the component"; parameter Boolean allowFlowReversal1 = true "= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)"; parameter Boolean allowFlowReversal2 = true "= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)"; parameter Modelica.SIunits.SpecificEnthalpy h_outflow_a1_start = Medium1.h_default "Start value for enthalpy flowing out of port a1"; parameter Modelica.SIunits.SpecificEnthalpy h_outflow_b1_start = Medium1.h_default "Start value for enthalpy flowing out of port b1"; parameter Modelica.SIunits.SpecificEnthalpy h_outflow_a2_start = Medium2.h_default "Start value for enthalpy flowing out of port a2"; parameter Modelica.SIunits.SpecificEnthalpy h_outflow_b2_start = Medium2.h_default "Start value for enthalpy flowing out of port b2"; Modelica.Fluid.Interfaces.FluidPort_a port_a1( redeclare final package Medium = Medium1, m_flow(min=if allowFlowReversal1 then -Modelica.Constants.inf else 0), h_outflow(start=h_outflow_a1_start)) "Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)"; Modelica.Fluid.Interfaces.FluidPort_b port_b1( redeclare final package Medium = Medium1, m_flow(max=if allowFlowReversal1 then +Modelica.Constants.inf else 0), h_outflow(start=h_outflow_b1_start)) "Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)"; Modelica.Fluid.Interfaces.FluidPort_a port_a2( redeclare final package Medium = Medium2, m_flow(min=if allowFlowReversal2 then -Modelica.Constants.inf else 0), h_outflow(start=h_outflow_a2_start)) "Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)"; Modelica.Fluid.Interfaces.FluidPort_b port_b2( redeclare final package Medium = Medium2, m_flow(max=if allowFlowReversal2 then +Modelica.Constants.inf else 0), h_outflow(start=h_outflow_b2_start)) "Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)"; end FourPort;

## Buildings.Fluid.Interfaces.FourPortHeatMassExchanger

Model transporting two fluid streams between four ports with storing mass or energy

### Information

This component transports two fluid streams between four ports. It provides the basic model for implementing a dynamic heat exchanger.

The model can be used as-is, although there will be no heat or mass transfer between the two fluid streams. To add heat transfer, heat flow can be added to the heat port of the two volumes. See for example Buildings.Fluid.Chillers.Carnot. To add moisture input into (or moisture output from) volume `vol2`, the model can be replaced as shown in Buildings.Fluid.HeatExchangers.BaseClasses.HexElement.

#### Implementation

The variable names follow the conventions used in Modelica.Fluid.HeatExchangers.BasicHX.

Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters (Parameters for flow resistance for models with four ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium1 | PartialMedium | Medium 1 in the component
replaceable package Medium2 | PartialMedium | Medium 2 in the component
MixingVolume | vol2 | redeclare Buildings.Fluid.Mi... | Volume for fluid 2
Nominal condition
MassFlowRate | m1_flow_nominal |  | Nominal mass flow rate [kg/s]
MassFlowRate | m2_flow_nominal |  | Nominal mass flow rate [kg/s]
Pressure | dp1_nominal |  | Pressure difference [Pa]
Pressure | dp2_nominal |  | Pressure difference [Pa]
Initialization
MassFlowRate | m1_flow.start | 0 | Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction) [kg/s]
Pressure | dp1.start | 0 | Pressure difference between port_a1 and port_b1 [Pa]
MassFlowRate | m2_flow.start | 0 | Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction) [kg/s]
Pressure | dp2.start | 0 | Pressure difference between port_a2 and port_b2 [Pa]
Assumptions
Boolean | allowFlowReversal1 | true | = true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean | allowFlowReversal2 | true | = true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy | h_outflow_a1_start | h1_outflow_start | Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy | h_outflow_b1_start | h1_outflow_start | Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy | h_outflow_a2_start | h2_outflow_start | Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy | h_outflow_b2_start | h2_outflow_start | Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate | m1_flow_small | 1E-4*abs(m1_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate | m2_flow_small | 1E-4*abs(m2_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Boolean | homotopyInitialization | true | = true, use homotopy method
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed
Flow resistance
Medium 1
Boolean | computeFlowResistance1 | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp1 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance1 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM1 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean | computeFlowResistance2 | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp2 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance2 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM2 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time | tau1 | 30 | Time constant at nominal flow [s]
Time | tau2 | 30 | Time constant at nominal flow [s]
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance
Dynamics | massDynamics | energyDynamics | Formulation of mass balance
Initialization
Medium 1
AbsolutePressure | p1_start | Medium1.p_default | Start value of pressure [Pa]
Temperature | T1_start | Medium1.T_default | Start value of temperature [K]
MassFraction | X1_start[Medium1.nX] | Medium1.X_default | Start value of mass fractions m_i/m [kg/kg]
ExtraProperty | C1_start[Medium1.nC] | fill(0, Medium1.nC) | Start value of trace substances
ExtraProperty | C1_nominal[Medium1.nC] | fill(1E-2, Medium1.nC) | Nominal value of trace substances. (Set to typical order of magnitude.)
Medium 2
AbsolutePressure | p2_start | Medium2.p_default | Start value of pressure [Pa]
Temperature | T2_start | Medium2.T_default | Start value of temperature [K]
MassFraction | X2_start[Medium2.nX] | Medium2.X_default | Start value of mass fractions m_i/m [kg/kg]
ExtraProperty | C2_start[Medium2.nC] | fill(0, Medium2.nC) | Start value of trace substances
ExtraProperty | C2_nominal[Medium2.nC] | fill(1E-2, Medium2.nC) | Nominal value of trace substances. (Set to typical order of magnitude.)

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a1 | Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b | port_b1 | Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a | port_a2 | Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b | port_b2 | Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

### Modelica definition

model FourPortHeatMassExchanger "Model transporting two fluid streams between four ports with storing mass or energy" extends Buildings.Fluid.Interfaces.PartialFourPortInterface( final h_outflow_a1_start = h1_outflow_start, final h_outflow_b1_start = h1_outflow_start, final h_outflow_a2_start = h2_outflow_start, final h_outflow_b2_start = h2_outflow_start); extends Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters( final computeFlowResistance1=true, final computeFlowResistance2=true); parameter Modelica.SIunits.Time tau1 = 30 "Time constant at nominal flow"; parameter Modelica.SIunits.Time tau2 = 30 "Time constant at nominal flow"; // Advanced parameter Boolean homotopyInitialization = true "= true, use homotopy method"; // Assumptions parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial "Formulation of energy balance"; parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics "Formulation of mass balance"; // Initialization parameter Medium1.AbsolutePressure p1_start = Medium1.p_default "Start value of pressure"; parameter Medium1.Temperature T1_start = Medium1.T_default "Start value of temperature"; parameter Medium1.MassFraction X1_start[Medium1.nX] = Medium1.X_default "Start value of mass fractions m_i/m"; parameter Medium1.ExtraProperty C1_start[Medium1.nC]( quantity=Medium1.extraPropertiesNames)=fill(0, Medium1.nC) "Start value of trace substances"; parameter Medium1.ExtraProperty C1_nominal[Medium1.nC]( quantity=Medium1.extraPropertiesNames) = fill(1E-2, Medium1.nC) "Nominal value of trace substances. (Set to typical order of magnitude.)"; parameter Medium2.AbsolutePressure p2_start = Medium2.p_default "Start value of pressure"; parameter Medium2.Temperature T2_start = Medium2.T_default "Start value of temperature"; parameter Medium2.MassFraction X2_start[Medium2.nX] = Medium2.X_default "Start value of mass fractions m_i/m"; parameter Medium2.ExtraProperty C2_start[Medium2.nC]( quantity=Medium2.extraPropertiesNames)=fill(0, Medium2.nC) "Start value of trace substances"; parameter Medium2.ExtraProperty C2_nominal[Medium2.nC]( quantity=Medium2.extraPropertiesNames) = fill(1E-2, Medium2.nC) "Nominal value of trace substances. (Set to typical order of magnitude.)"; Buildings.Fluid.MixingVolumes.MixingVolume vol1( redeclare final package Medium = Medium1, nPorts = 2, V=m1_flow_nominal*tau1/rho1_nominal, final m_flow_nominal=m1_flow_nominal, energyDynamics=if tau1 > Modelica.Constants.eps then energyDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, massDynamics=if tau1 > Modelica.Constants.eps then massDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, final p_start=p1_start, final T_start=T1_start, final X_start=X1_start, final C_start=C1_start, final C_nominal=C1_nominal, final mSenFac=1) "Volume for fluid 1"; replaceable Buildings.Fluid.MixingVolumes.MixingVolume vol2 constrainedby Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume( redeclare final package Medium = Medium2, nPorts = 2, V=m2_flow_nominal*tau2/rho2_nominal, final mSenFac=1, final m_flow_nominal = m2_flow_nominal, energyDynamics=if tau2 > Modelica.Constants.eps then energyDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, massDynamics=if tau2 > Modelica.Constants.eps then massDynamics else Modelica.Fluid.Types.Dynamics.SteadyState, final p_start=p2_start, final T_start=T2_start, final X_start=X2_start, final C_start=C2_start, final C_nominal=C2_nominal) "Volume for fluid 2"; Modelica.SIunits.HeatFlowRate Q1_flow = vol1.heatPort.Q_flow "Heat flow rate into medium 1"; Modelica.SIunits.HeatFlowRate Q2_flow = vol2.heatPort.Q_flow "Heat flow rate into medium 2"; Buildings.Fluid.FixedResistances.FixedResistanceDpM preDro1( redeclare final package Medium = Medium1, final use_dh=false, final m_flow_nominal=m1_flow_nominal, final deltaM=deltaM1, final allowFlowReversal=allowFlowReversal1, final show_T=false, final from_dp=from_dp1, final linearized=linearizeFlowResistance1, final homotopyInitialization=homotopyInitialization, final dp_nominal=dp1_nominal, final dh=1, final ReC=4000) "Pressure drop model for fluid 1"; Buildings.Fluid.FixedResistances.FixedResistanceDpM preDro2( redeclare final package Medium = Medium2, final use_dh=false, final m_flow_nominal=m2_flow_nominal, final deltaM=deltaM2, final allowFlowReversal=allowFlowReversal2, final show_T=false, final from_dp=from_dp2, final linearized=linearizeFlowResistance2, final homotopyInitialization=homotopyInitialization, final dp_nominal=dp2_nominal, final dh=1, final ReC=4000) "Pressure drop model for fluid 2"; protected parameter Medium1.ThermodynamicState sta1_nominal=Medium1.setState_pTX( T=Medium1.T_default, p=Medium1.p_default, X=Medium1.X_default); parameter Modelica.SIunits.Density rho1_nominal=Medium1.density(sta1_nominal) "Density, used to compute fluid volume"; parameter Medium2.ThermodynamicState sta2_nominal=Medium2.setState_pTX( T=Medium2.T_default, p=Medium2.p_default, X=Medium2.X_default); parameter Modelica.SIunits.Density rho2_nominal=Medium2.density(sta2_nominal) "Density, used to compute fluid volume"; parameter Medium1.ThermodynamicState sta1_start=Medium1.setState_pTX( T=T1_start, p=p1_start, X=X1_start); parameter Modelica.SIunits.SpecificEnthalpy h1_outflow_start = Medium1.specificEnthalpy(sta1_start) "Start value for outflowing enthalpy"; parameter Medium2.ThermodynamicState sta2_start=Medium2.setState_pTX( T=T2_start, p=p2_start, X=X2_start); parameter Modelica.SIunits.SpecificEnthalpy h2_outflow_start = Medium2.specificEnthalpy(sta2_start) "Start value for outflowing enthalpy"; initial algorithm // Check for tau1 assert((energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau1 > Modelica.Constants.eps, "The parameter tau1, or the volume of the model from which tau may be derived, is unreasonably small. You need to set energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau1 = " + String(tau1) + "\n"); assert((massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau1 > Modelica.Constants.eps, "The parameter tau1, or the volume of the model from which tau may be derived, is unreasonably small. You need to set massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau1 = " + String(tau1) + "\n"); // Check for tau2 assert((energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau2 > Modelica.Constants.eps, "The parameter tau2, or the volume of the model from which tau may be derived, is unreasonably small. You need to set energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau2 = " + String(tau2) + "\n"); assert((massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau2 > Modelica.Constants.eps, "The parameter tau2, or the volume of the model from which tau may be derived, is unreasonably small. You need to set massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau2 = " + String(tau2) + "\n"); equation connect(vol1.ports[2], port_b1); connect(vol2.ports[2], port_b2); connect(port_a1, preDro1.port_a); connect(preDro1.port_b, vol1.ports[1]); connect(port_a2, preDro2.port_a); connect(preDro2.port_b, vol2.ports[1]); end FourPortHeatMassExchanger;

## Buildings.Fluid.Interfaces.PartialFourPortInterface

Partial model transporting fluid between two ports without storing mass or energy

### Information

This component defines the interface for models that transport two fluid streams between four ports. It is similar to Buildings.Fluid.Interfaces.PartialTwoPortInterface, but it has four ports instead of two.

The model is used by other models in this package that add heat transfer, mass transfer and pressure drop equations.

Extends from Buildings.Fluid.Interfaces.FourPort (Partial model with four ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium1 | PartialMedium | Medium 1 in the component
replaceable package Medium2 | PartialMedium | Medium 2 in the component
Nominal condition
MassFlowRate | m1_flow_nominal |  | Nominal mass flow rate [kg/s]
MassFlowRate | m2_flow_nominal |  | Nominal mass flow rate [kg/s]
Assumptions
Boolean | allowFlowReversal1 | true | = true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean | allowFlowReversal2 | true | = true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy | h_outflow_a1_start | Medium1.h_default | Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy | h_outflow_b1_start | Medium1.h_default | Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy | h_outflow_a2_start | Medium2.h_default | Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy | h_outflow_b2_start | Medium2.h_default | Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate | m1_flow_small | 1E-4*abs(m1_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate | m2_flow_small | 1E-4*abs(m2_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a1 | Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b | port_b1 | Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a | port_a2 | Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b | port_b2 | Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

### Modelica definition

partial model PartialFourPortInterface "Partial model transporting fluid between two ports without storing mass or energy" extends Buildings.Fluid.Interfaces.FourPort; parameter Modelica.SIunits.MassFlowRate m1_flow_nominal(min=0) "Nominal mass flow rate"; parameter Modelica.SIunits.MassFlowRate m2_flow_nominal(min=0) "Nominal mass flow rate"; parameter Medium1.MassFlowRate m1_flow_small(min=0) = 1E-4*abs(m1_flow_nominal) "Small mass flow rate for regularization of zero flow"; parameter Medium2.MassFlowRate m2_flow_small(min=0) = 1E-4*abs(m2_flow_nominal) "Small mass flow rate for regularization of zero flow"; // Diagnostics parameter Boolean show_T = false "= true, if actual temperature at port is computed"; Medium1.MassFlowRate m1_flow(start=0) = port_a1.m_flow "Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction)"; Modelica.SIunits.Pressure dp1(start=0, displayUnit="Pa") "Pressure difference between port_a1 and port_b1"; Medium2.MassFlowRate m2_flow(start=0) = port_a2.m_flow "Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction)"; Modelica.SIunits.Pressure dp2(start=0, displayUnit="Pa") "Pressure difference between port_a2 and port_b2"; Medium1.ThermodynamicState sta_a1= Medium1.setState_phX(port_a1.p, noEvent(actualStream(port_a1.h_outflow)), noEvent(actualStream(port_a1.Xi_outflow))) if show_T "Medium properties in port_a1"; Medium1.ThermodynamicState sta_b1= Medium1.setState_phX(port_b1.p, noEvent(actualStream(port_b1.h_outflow)), noEvent(actualStream(port_b1.Xi_outflow))) if show_T "Medium properties in port_b1"; Medium2.ThermodynamicState sta_a2= Medium2.setState_phX(port_a2.p, noEvent(actualStream(port_a2.h_outflow)), noEvent(actualStream(port_a2.Xi_outflow))) if show_T "Medium properties in port_a2"; Medium2.ThermodynamicState sta_b2= Medium2.setState_phX(port_b2.p, noEvent(actualStream(port_b2.h_outflow)), noEvent(actualStream(port_b2.Xi_outflow))) if show_T "Medium properties in port_b2"; protected Medium1.ThermodynamicState state_a1_inflow= Medium1.setState_phX(port_a1.p, inStream(port_a1.h_outflow), inStream(port_a1.Xi_outflow)) "state for medium inflowing through port_a1"; Medium1.ThermodynamicState state_b1_inflow= Medium1.setState_phX(port_b1.p, inStream(port_b1.h_outflow), inStream(port_b1.Xi_outflow)) "state for medium inflowing through port_b1"; Medium2.ThermodynamicState state_a2_inflow= Medium2.setState_phX(port_a2.p, inStream(port_a2.h_outflow), inStream(port_a2.Xi_outflow)) "state for medium inflowing through port_a2"; Medium2.ThermodynamicState state_b2_inflow= Medium2.setState_phX(port_b2.p, inStream(port_b2.h_outflow), inStream(port_b2.Xi_outflow)) "state for medium inflowing through port_b2"; equation dp1 = port_a1.p - port_b1.p; dp2 = port_a2.p - port_b2.p; end PartialFourPortInterface;

## Buildings.Fluid.Interfaces.PartialTwoPort

Partial component with two ports

### Information

This partial model defines an interface for components with two ports. The treatment of the design flow direction and of flow reversal are predefined based on the parameter `allowFlowReversal`. The component may transport fluid and may have internal storage for a given fluid `Medium`.

An extending model providing direct access to internal storage of mass or energy through `port_a` or `port_b` should redefine the protected parameters `port_a_exposesState` and `port_b_exposesState` appropriately. This will be visualized at the port icons, in order to improve the understanding of fluid model diagrams.

#### Implementation

This model is similar to Modelica.Fluid.Interfaces.PartialTwoPort but it does not use the `outer system` declaration. This declaration is omitted as in building energy simulation, many models use multiple media, an in practice, users have not used this global definition to assign parameters.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | Modelica.Media.Interfaces.Pa... | Medium in the component
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

### Connectors

Type | Name | Description
--- | --- | ---
replaceable package Medium | Medium in the component
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b)

### Modelica definition

partial model PartialTwoPort "Partial component with two ports" import Modelica.Constants; replaceable package Medium = Modelica.Media.Interfaces.PartialMedium "Medium in the component"; parameter Boolean allowFlowReversal = true "= true to allow flow reversal, false restricts to design direction (port_a -> port_b)"; Modelica.Fluid.Interfaces.FluidPort_a port_a( redeclare final package Medium = Medium, m_flow(min=if allowFlowReversal then -Constants.inf else 0)) "Fluid connector a (positive design flow direction is from port_a to port_b)"; Modelica.Fluid.Interfaces.FluidPort_b port_b( redeclare final package Medium = Medium, m_flow(max=if allowFlowReversal then +Constants.inf else 0)) "Fluid connector b (positive design flow direction is from port_a to port_b)"; // Model structure, e.g., used for visualization protected parameter Boolean port_a_exposesState = false "= true if port_a exposes the state of a fluid volume"; parameter Boolean port_b_exposesState = false "= true if port_b.p exposes the state of a fluid volume"; parameter Boolean showDesignFlowDirection = true "= false to hide the arrow in the model icon"; end PartialTwoPort;

## Buildings.Fluid.Interfaces.PartialTwoPortInterface

Partial model transporting fluid between two ports without storing mass or energy

### Information

This component defines the interface for models that transports a fluid between two ports. It is similar to Modelica.Fluid.Interfaces.PartialTwoPortTransport, but it does not include the species balance

      port_b.Xi_outflow = inStream(port_a.Xi_outflow);

Thus, it can be used as a base class for a heat and mass transfer component

The model is used by other models in this package that add heat transfer, mass transfer and pressure drop equations. See for example Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger.

Extends from Buildings.Fluid.Interfaces.PartialTwoPort (Partial component with two ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate [kg/s]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed

### Modelica definition

partial model PartialTwoPortInterface "Partial model transporting fluid between two ports without storing mass or energy" extends Buildings.Fluid.Interfaces.PartialTwoPort( port_a(p(start=Medium.p_default)), port_b(p(start=Medium.p_default))); parameter Modelica.SIunits.MassFlowRate m_flow_nominal "Nominal mass flow rate"; parameter Modelica.SIunits.MassFlowRate m_flow_small(min=0) = 1E-4*abs(m_flow_nominal) "Small mass flow rate for regularization of zero flow"; // Diagnostics parameter Boolean show_T = false "= true, if actual temperature at port is computed"; Modelica.SIunits.MassFlowRate m_flow(start=0) = port_a.m_flow "Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction)"; Modelica.SIunits.Pressure dp(start=0, displayUnit="Pa") "Pressure difference between port_a and port_b"; Medium.ThermodynamicState sta_a= Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) if show_T "Medium properties in port_a"; Medium.ThermodynamicState sta_b= Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) if show_T "Medium properties in port_b"; equation dp = port_a.p - port_b.p; end PartialTwoPortInterface;

## Buildings.Fluid.Interfaces.PartialTwoPortTransport

Partial element transporting fluid between two ports without storage of mass or energy

### Information

This component transports fluid between its two ports, without storing mass or energy. Energy may be exchanged with the environment though, e.g., in the form of work. `PartialTwoPortTransport` is intended as base class for devices like orifices, valves and simple fluid machines.

Three equations need to be added by an extending class using this component:

- The momentum balance specifying the relationship between the pressure drop `dp` and the mass flow rate `m_flow`,
- `port_b.h_outflow` for flow in design direction, and
- `port_a.h_outflow` for flow in reverse direction.

Moreover appropriate values shall be assigned to the following parameters:

- `dp_start` for a guess of the pressure drop
- `m_flow_small` for regularization of zero flow.

#### Implementation

This is similar to Modelica.Fluid.Interfaces.PartialTwoPortTransport except that it does not use the `outer system` declaration. This declaration is omitted as in building energy simulation, many models use multiple media, an in practice, users have not used this global definition to assign parameters.

Extends from Buildings.Fluid.Interfaces.PartialTwoPort (Partial component with two ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
AbsolutePressure | dp_start | 0 | Guess value of dp = port_a.p - port_b.p [Pa]
MassFlowRate | m_flow_start | 0 | Guess value of m_flow = port_a.m_flow [kg/s]
MassFlowRate | m_flow_small |  | Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean | show_T | true | = true, if temperatures at port_a and port_b are computed
Boolean | show_V_flow | true | = true, if volume flow rate at inflowing port is computed

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b)

### Modelica definition

partial model PartialTwoPortTransport "Partial element transporting fluid between two ports without storage of mass or energy" extends Buildings.Fluid.Interfaces.PartialTwoPort( final port_a_exposesState=false, final port_b_exposesState=false); // Advanced // Note: value of dp_start shall be refined by derived model, // based on local dp_nominal parameter Medium.AbsolutePressure dp_start = 0 "Guess value of dp = port_a.p - port_b.p"; parameter Medium.MassFlowRate m_flow_start = 0 "Guess value of m_flow = port_a.m_flow"; // Note: value of m_flow_small shall be refined by derived model, // based on local m_flow_nominal parameter Medium.MassFlowRate m_flow_small "Small mass flow rate for regularization of zero flow"; // Diagnostics parameter Boolean show_T = true "= true, if temperatures at port_a and port_b are computed"; parameter Boolean show_V_flow = true "= true, if volume flow rate at inflowing port is computed"; // Variables Medium.MassFlowRate m_flow( min=if allowFlowReversal then -Modelica.Constants.inf else 0, start = m_flow_start) "Mass flow rate in design flow direction"; Modelica.SIunits.Pressure dp(start=dp_start) "Pressure difference between port_a and port_b (= port_a.p - port_b.p)"; Modelica.SIunits.VolumeFlowRate V_flow= m_flow/Modelica.Fluid.Utilities.regStep(m_flow, Medium.density(state_a), Medium.density(state_b), m_flow_small) if show_V_flow "Volume flow rate at inflowing port (positive when flow from port_a to port_b)"; Medium.Temperature port_a_T= Modelica.Fluid.Utilities.regStep(port_a.m_flow, Medium.temperature(state_a), Medium.temperature(Medium.setState_phX(port_a.p, port_a.h_outflow, port_a.Xi_outflow)), m_flow_small) if show_T "Temperature close to port_a, if show_T = true"; Medium.Temperature port_b_T= Modelica.Fluid.Utilities.regStep(port_b.m_flow, Medium.temperature(state_b), Medium.temperature(Medium.setState_phX(port_b.p, port_b.h_outflow, port_b.Xi_outflow)), m_flow_small) if show_T "Temperature close to port_b, if show_T = true"; protected Medium.ThermodynamicState state_a = Medium.setState_phX( port_a.p, inStream(port_a.h_outflow), inStream(port_a.Xi_outflow)) if show_T or show_V_flow "State for medium inflowing through port_a"; Medium.ThermodynamicState state_b = Medium.setState_phX( port_b.p, inStream(port_b.h_outflow), inStream(port_b.Xi_outflow)) if show_T or show_V_flow "State for medium inflowing through port_b"; equation // Pressure drop in design flow direction dp = port_a.p - port_b.p; // Design direction of mass flow rate m_flow = port_a.m_flow; assert(m_flow > -m_flow_small or allowFlowReversal, "Reverting flow occurs even though allowFlowReversal is false"); // Mass balance (no storage) port_a.m_flow + port_b.m_flow = 0; // Transport of substances port_a.Xi_outflow = inStream(port_b.Xi_outflow); port_b.Xi_outflow = inStream(port_a.Xi_outflow); port_a.C_outflow = inStream(port_b.C_outflow); port_b.C_outflow = inStream(port_a.C_outflow); end PartialTwoPortTransport;

## Buildings.Fluid.Interfaces.PrescribedOutletState

Component that assigns the outlet fluid property at port_a based on an input signal

### Information

This model sets the temperature of the medium that leaves `port_a` to the value given by the input `TSet`, subject to optional limitations on the heating and cooling capacity.

In case of reverse flow, the set point temperature is still applied to the fluid that leaves `port_b`.

If the parameter `energyDynamics` is not equal to `Modelica.Fluid.Types.Dynamics.SteadyState`, the component models the dynamic response using a first order differential equation. The time constant of the component is equal to the parameter `tau`. This time constant is adjusted based on the mass flow rate using

τeff = τ |ṁ| ⁄ ṁnom

where τeff is the effective time constant for the given mass flow rate ṁ and τ is the time constant at the nominal mass flow rate ṁnom. This type of dynamics is equal to the dynamics that a completely mixed control volume would have.

This model has no pressure drop. See Buildings.Fluid.HeatExchangers.HeaterCooler_T for a model that instantiates this model and that has a pressure drop.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortTransport (Partial element transporting fluid between two ports without storage of mass or energy), Buildings.Fluid.Interfaces.PrescribedOutletStateParameters (Parameters for models with prescribed outlet state).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
HeatFlowRate | Q_flow_maxHeat | Modelica.Constants.inf | Maximum heat flow rate for heating (positive) [W]
HeatFlowRate | Q_flow_maxCool | -Modelica.Constants.inf | Maximum heat flow rate for cooling (negative) [W]
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate, used for regularization near zero flow [kg/s]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
AbsolutePressure | dp_start | 0 | Guess value of dp = port_a.p - port_b.p [Pa]
MassFlowRate | m_flow_start | 0 | Guess value of m_flow = port_a.m_flow [kg/s]
MassFlowRate | m_flow_small |  | Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean | show_T | false | = true, if temperatures at port_a and port_b are computed
Boolean | show_V_flow | false | = true, if volume flow rate at inflowing port is computed
Dynamics
Time | tau | 10 | Time constant at nominal flow rate (used if energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState) [s]
Initialization
Temperature | T_start | Medium.T_default | Initial or guess value of set point [K]
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b)
input RealInput | TSet | Set point temperature of the fluid that leaves port_b [K]
output RealOutput | Q_flow | Heat added to the fluid (if flow is from port_a to port_b) [W]

### Modelica definition

model PrescribedOutletState "Component that assigns the outlet fluid property at port_a based on an input signal" extends Buildings.Fluid.Interfaces.PartialTwoPortTransport( final dp_start=0, show_T=false, show_V_flow=false); extends Buildings.Fluid.Interfaces.PrescribedOutletStateParameters( T_start=Medium.T_default); Modelica.Blocks.Interfaces.RealInput TSet(unit="K", displayUnit="degC") "Set point temperature of the fluid that leaves port_b"; Modelica.Blocks.Interfaces.RealOutput Q_flow(unit="W") "Heat added to the fluid (if flow is from port_a to port_b)"; protected parameter Modelica.SIunits.SpecificHeatCapacity cp_default= Medium.specificHeatCapacityCp( Medium.setState_pTX( p=Medium.p_default, T=Medium.T_default, X=Medium.X_default)) "Specific heat capacity at default medium state"; parameter Boolean restrictHeat = Q_flow_maxHeat <> Modelica.Constants.inf "Flag, true if maximum heating power is restricted"; parameter Boolean restrictCool = Q_flow_maxCool <> -Modelica.Constants.inf "Flag, true if maximum cooling power is restricted"; parameter Modelica.SIunits.SpecificEnthalpy deltah= cp_default*m_flow_small*0.01 "Small value for deltah used for regularization"; final parameter Boolean dynamic = tau > 1E-10 or tau < -1E-10 "Flag, true if the sensor is a dynamic sensor"; Modelica.SIunits.MassFlowRate m_flow_pos "Mass flow rate, or zero if reverse flow"; Modelica.SIunits.MassFlowRate m_flow_limited "Mass flow rate bounded away from zero"; Modelica.SIunits.SpecificEnthalpy hSet "Set point for enthalpy leaving port_b"; Modelica.SIunits.Temperature T "Temperature of outlet state assuming unlimited capacity and taking dynamics into account"; Modelica.SIunits.SpecificEnthalpy dhSetAct "Actual enthalpy difference from port_a to port_b"; Real k(start=1) "Gain to take flow rate into account for sensor time constant"; Real mNor_flow "Normalized mass flow rate"; initial equation if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then der(T) = 0; elseif energyDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then T = T_start; end if; if energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState then assert(tau > 1E-5, "Time constant tau is unreasonably small for dynamic balance. Check model parameters."); end if; equation if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then mNor_flow = 1; k = 1; T=TSet; else mNor_flow = port_a.m_flow/m_flow_nominal; k = Modelica.Fluid.Utilities.regStep(x=port_a.m_flow, y1= mNor_flow, y2=-mNor_flow, x_small=m_flow_small); der(T) = (TSet-T)*k/tau; end if; // Set point for outlet enthalpy without any capacity limitation hSet = Medium.specificEnthalpy( Medium.setState_pTX( p= port_a.p, T= T, X= inStream(port_a.Xi_outflow))); m_flow_pos = Buildings.Utilities.Math.Functions.smoothMax( x1=m_flow, x2=0, deltaX=m_flow_small); // Compute how much dH may need to be reduced. if not restrictHeat and not restrictCool then // No capacity limit dhSetAct = 0; port_b.h_outflow = hSet; m_flow_limited = 0; Q_flow = m_flow_pos*(hSet-inStream(port_a.h_outflow)); else m_flow_limited = Buildings.Utilities.Math.Functions.smoothMax( x1= port_a.m_flow, x2= m_flow_small, deltaX=m_flow_small/2); if restrictHeat and restrictCool then // Capacity limits for heating and cooling dhSetAct = Buildings.Utilities.Math.Functions.smoothLimit( x=hSet-inStream(port_a.h_outflow), l=Q_flow_maxCool / m_flow_limited, u=Q_flow_maxHeat / m_flow_limited, deltaX=deltah); elseif restrictHeat then // Capacity limit for heating only dhSetAct = Buildings.Utilities.Math.Functions.smoothMin( x1=hSet-inStream(port_a.h_outflow), x2=Q_flow_maxHeat / m_flow_limited, deltaX=deltah); else // Capacity limit for cooling only dhSetAct = Buildings.Utilities.Math.Functions.smoothMax( x1=hSet-inStream(port_a.h_outflow), x2=Q_flow_maxCool / m_flow_limited, deltaX=deltah); end if; port_b.h_outflow = inStream(port_a.h_outflow) + dhSetAct; Q_flow = m_flow_pos*dhSetAct; end if; // Outflowing property at port_a is unaffected by this model. port_a.h_outflow = inStream(port_b.h_outflow); // No pressure drop dp = 0; end PrescribedOutletState;

## Buildings.Fluid.Interfaces.StaticFourPortHeatMassExchanger

Partial model transporting two fluid streams between four ports without storing mass or energy

### Information

This component transports two fluid streams between four ports, without storing mass or energy. It is similar to Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger, but it has four ports instead of two.

If `dpN_nominal > Modelica.Constants.eps`, where `N` denotes the fluid 1 or 2, then the model computes pressure drop due to flow friction in the respective fluid stream. The pressure drop is defined by a quadratic function that goes through the point `(mN_flow_nominal, dpN_nominal)`. At `|mN_flow| < deltaMN * mN_flow_nominal`, the pressure drop vs. flow relation is linearized. If the parameter `linearizeFlowResistanceN` is set to true, then the whole pressure drop vs. flow resistance curve is linearized.

#### Implementation

This model uses inputs and constants that need to be set by models that extend or instantiate this model. The following inputs need to be assigned, where `N` denotes `1` or `2`:

- `QN_flow`, which is the heat flow rate added to the medium N.
- `mWatN_flow`, which is the moisture mass flow rate added to the medium N.

Set the constant `sensibleOnlyN=true` if the model that extends or instantiates this model sets `mWatN_flow = 0`.

Note that the model does not implement `0 = Q1_flow + Q2_flow` or `0 = mXi1_flow + mXi2_flow`. If there is no heat or mass transfer with the environment, then a model that extends this model needs to provide these equations.

Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters (Parameters for flow resistance for models with four ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium1 | PartialMedium | Medium 1 in the component
replaceable package Medium2 | PartialMedium | Medium 2 in the component
Boolean | sensibleOnly1 |  | Set to true if sensible exchange only for medium 1
Boolean | sensibleOnly2 |  | Set to true if sensible exchange only for medium 2
Nominal condition
MassFlowRate | m1_flow_nominal |  | Nominal mass flow rate [kg/s]
MassFlowRate | m2_flow_nominal |  | Nominal mass flow rate [kg/s]
Pressure | dp1_nominal |  | Pressure difference [Pa]
Pressure | dp2_nominal |  | Pressure difference [Pa]
Initialization
MassFlowRate | m1_flow.start | 0 | Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction) [kg/s]
Pressure | dp1.start | 0 | Pressure difference between port_a1 and port_b1 [Pa]
MassFlowRate | m2_flow.start | 0 | Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction) [kg/s]
Pressure | dp2.start | 0 | Pressure difference between port_a2 and port_b2 [Pa]
Assumptions
Boolean | allowFlowReversal1 | true | = true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean | allowFlowReversal2 | true | = true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy | h_outflow_a1_start | Medium1.h_default | Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy | h_outflow_b1_start | Medium1.h_default | Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy | h_outflow_a2_start | Medium2.h_default | Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy | h_outflow_b2_start | Medium2.h_default | Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate | m1_flow_small | 1E-4*abs(m1_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate | m2_flow_small | 1E-4*abs(m2_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Boolean | homotopyInitialization | true | = true, use homotopy method
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed
Flow resistance
Medium 1
Boolean | computeFlowResistance1 | (dp1_nominal > Modelica.Cons... | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp1 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance1 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM1 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean | computeFlowResistance2 | (dp2_nominal > Modelica.Cons... | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp2 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance2 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM2 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a1 | Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b | port_b1 | Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a | port_a2 | Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b | port_b2 | Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

### Modelica definition

model StaticFourPortHeatMassExchanger "Partial model transporting two fluid streams between four ports without storing mass or energy" extends Buildings.Fluid.Interfaces.PartialFourPortInterface; extends Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters( final computeFlowResistance1=(dp1_nominal > Modelica.Constants.eps), final computeFlowResistance2=(dp2_nominal > Modelica.Constants.eps)); parameter Boolean homotopyInitialization = true "= true, use homotopy method"; input Modelica.SIunits.HeatFlowRate Q1_flow "Heat transferred into the medium 1"; input Medium1.MassFlowRate mWat1_flow "Moisture mass flow rate added to the medium 1"; input Modelica.SIunits.HeatFlowRate Q2_flow "Heat transferred into the medium 2"; input Medium2.MassFlowRate mWat2_flow "Moisture mass flow rate added to the medium 2"; constant Boolean sensibleOnly1 "Set to true if sensible exchange only for medium 1"; constant Boolean sensibleOnly2 "Set to true if sensible exchange only for medium 2"; protected Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger bal1( final sensibleOnly = sensibleOnly1, redeclare final package Medium=Medium1, final m_flow_nominal = m1_flow_nominal, final dp_nominal = dp1_nominal, final allowFlowReversal = allowFlowReversal1, final m_flow_small = m1_flow_small, final homotopyInitialization = homotopyInitialization, final from_dp = from_dp1, final linearizeFlowResistance = linearizeFlowResistance1, final deltaM = deltaM1, final Q_flow = Q1_flow, final mWat_flow = mWat1_flow) "Model for heat, mass, species, trace substance and pressure balance of stream 1"; Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger bal2( final sensibleOnly = sensibleOnly2, redeclare final package Medium=Medium2, final m_flow_nominal = m2_flow_nominal, final dp_nominal = dp2_nominal, final allowFlowReversal = allowFlowReversal2, final m_flow_small = m2_flow_small, final homotopyInitialization = homotopyInitialization, final from_dp = from_dp2, final linearizeFlowResistance = linearizeFlowResistance2, final deltaM = deltaM2, final Q_flow = Q2_flow, final mWat_flow = mWat2_flow) "Model for heat, mass, species, trace substance and pressure balance of stream 2"; equation connect(bal1.port_a, port_a1); connect(bal1.port_b, port_b1); connect(bal2.port_a, port_a2); connect(bal2.port_b, port_b2); end StaticFourPortHeatMassExchanger;

## Buildings.Fluid.Interfaces.StaticTwoPortConservationEquation

Partial model for static energy and mass conservation equations

### Information

This model transports fluid between its two ports, without storing mass or energy. It implements a steady-state conservation equation for energy and mass fractions. The model has zero pressure drop between its ports.

#### Implementation

Input connectors of the model are

- `Q_flow`, which is the sensible plus latent heat flow rate added to the medium, and
- `mWat_flow`, which is the moisture mass flow rate added to the medium.

The model can only be used as a steady-state model with two fluid ports. For a model with a dynamic balance, and more fluid ports, use Buildings.Fluid.Interfaces.ConservationEquation.

Set the constant `sensibleOnly=true` if the model that extends or instantiates this model sets `mWat_flow = 0`.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Boolean | sensibleOnly |  | Set to true if sensible exchange only
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate [kg/s]
Initialization
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b)
input RealInput | Q_flow | Sensible plus latent heat flow rate transferred into the medium [W]
input RealInput | mWat_flow | Moisture mass flow rate added to the medium [kg/s]
output RealOutput | hOut | Leaving temperature of the component [J/kg]
output RealOutput | XiOut[Medium.nXi] | Leaving species concentration of the component [1]
output RealOutput | COut[Medium.nC] | Leaving trace substances of the component

### Modelica definition

model StaticTwoPortConservationEquation "Partial model for static energy and mass conservation equations" extends Buildings.Fluid.Interfaces.PartialTwoPortInterface( showDesignFlowDirection = false); constant Boolean sensibleOnly "Set to true if sensible exchange only"; Modelica.Blocks.Interfaces.RealInput Q_flow(unit="W") "Sensible plus latent heat flow rate transferred into the medium"; Modelica.Blocks.Interfaces.RealInput mWat_flow(unit="kg/s") "Moisture mass flow rate added to the medium"; // Outputs that are needed in models that extend this model Modelica.Blocks.Interfaces.RealOutput hOut(unit="J/kg", start=Medium.specificEnthalpy_pTX( p=Medium.p_default, T=Medium.T_default, X=Medium.X_default)) "Leaving temperature of the component"; Modelica.Blocks.Interfaces.RealOutput XiOut[Medium.nXi](each unit="1", each min=0, each max=1) "Leaving species concentration of the component"; Modelica.Blocks.Interfaces.RealOutput COut[Medium.nC](each min=0) "Leaving trace substances of the component"; constant Boolean use_safeDivision=true "Set to true to improve numerical robustness"; protected Real m_flowInv(unit="s/kg") "Regularization of 1/m_flow"; Modelica.SIunits.MassFlowRate mXi_flow[Medium.nXi] "Mass flow rates of independent substances added to the medium"; // Parameters that is used to construct the vector mXi_flow final parameter Real s[Medium.nXi] = {if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i], string2="Water", caseSensitive=false) then 1 else 0 for i in 1:Medium.nXi} "Vector with zero everywhere except where species is"; initial equation // Assert that the substance with name 'water' has been found. assert(Medium.nXi == 0 or abs(sum(s)-1) < 1e-5, "If Medium.nXi > 1, then substance 'water' must be present for one component.'" + Medium.mediumName + "'.\n" + "Check medium model."); equation // Species flow rate from connector mWat_flow mXi_flow = mWat_flow * s; // Regularization of m_flow around the origin to avoid a division by zero if use_safeDivision then m_flowInv = Buildings.Utilities.Math.Functions.inverseXRegularized(x=port_a.m_flow, delta=m_flow_small/1E3); else m_flowInv = 0; // m_flowInv is not used if use_safeDivision = false. end if; if allowFlowReversal then // Formulate hOut using spliceFunction. This avoids an event iteration. // The introduced error is small because deltax=m_flow_small/1e3 hOut = Buildings.Utilities.Math.Functions.spliceFunction(pos=port_b.h_outflow, neg=port_a.h_outflow, x=port_a.m_flow, deltax=m_flow_small/1E3); XiOut = Buildings.Utilities.Math.Functions.spliceFunction(pos=port_b.Xi_outflow, neg=port_a.Xi_outflow, x=port_a.m_flow, deltax=m_flow_small/1E3); COut = Buildings.Utilities.Math.Functions.spliceFunction(pos=port_b.C_outflow, neg=port_a.C_outflow, x=port_a.m_flow, deltax=m_flow_small/1E3); else hOut = port_b.h_outflow; XiOut = port_b.Xi_outflow; COut = port_b.C_outflow; end if; ////////////////////////////////////////////////////////////////////////////////////////// // Energy balance and mass balance if sensibleOnly then // Mass balance port_a.m_flow = -port_b.m_flow; // Energy balance if use_safeDivision then port_b.h_outflow = inStream(port_a.h_outflow) + Q_flow * m_flowInv; port_a.h_outflow = inStream(port_b.h_outflow) - Q_flow * m_flowInv; else port_a.m_flow * (inStream(port_a.h_outflow) - port_b.h_outflow) = -Q_flow; port_a.m_flow * (inStream(port_b.h_outflow) - port_a.h_outflow) = +Q_flow; end if; // Transport of species port_a.Xi_outflow = inStream(port_b.Xi_outflow); port_b.Xi_outflow = inStream(port_a.Xi_outflow); // Transport of trace substances port_a.C_outflow = inStream(port_b.C_outflow); port_b.C_outflow = inStream(port_a.C_outflow); else // Mass balance (no storage) port_a.m_flow + port_b.m_flow = -mWat_flow; // Energy balance. // This equation is approximate since m_flow = port_a.m_flow is used for the mass flow rate // at both ports. Since mWat_flow << m_flow, the error is small. if use_safeDivision then port_b.h_outflow = inStream(port_a.h_outflow) + Q_flow * m_flowInv; port_a.h_outflow = inStream(port_b.h_outflow) - Q_flow * m_flowInv; // Transport of species port_b.Xi_outflow = inStream(port_a.Xi_outflow) + mXi_flow * m_flowInv; port_a.Xi_outflow = inStream(port_b.Xi_outflow) - mXi_flow * m_flowInv; else port_a.m_flow * (inStream(port_a.h_outflow) - port_b.h_outflow) = -Q_flow; port_a.m_flow * (inStream(port_b.h_outflow) - port_a.h_outflow) = +Q_flow; // Transport of species port_a.m_flow * (inStream(port_a.Xi_outflow) - port_b.Xi_outflow) = -mXi_flow; port_a.m_flow * (inStream(port_b.Xi_outflow) - port_a.Xi_outflow) = +mXi_flow; end if; // Transport of trace substances port_a.m_flow*port_a.C_outflow = -port_b.m_flow*inStream(port_b.C_outflow); port_b.m_flow*port_b.C_outflow = -port_a.m_flow*inStream(port_a.C_outflow); end if; // sensibleOnly ////////////////////////////////////////////////////////////////////////////////////////// // No pressure drop in this model port_a.p = port_b.p; end StaticTwoPortConservationEquation;

## Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger

Partial model transporting fluid between two ports without storing mass or energy

### Information

This component transports fluid between its two ports, without storing mass or energy. It is based on Modelica.Fluid.Interfaces.PartialTwoPortTransport but it does use a different implementation for handling reverse flow because in this component, mass flow rate can be added or removed from the medium.

If `dp_nominal > Modelica.Constants.eps`, this component computes pressure drop due to flow friction. The pressure drop is defined by a quadratic function that goes through the point `(m_flow_nominal, dp_nominal)`. At `|m_flow| < deltaM * m_flow_nominal`, the pressure drop vs. flow relation is linearized. If the parameter `linearizeFlowResistance` is set to true, then the whole pressure drop vs. flow resistance curve is linearized.

#### Implementation

This model uses inputs and constants that need to be set by models that extend or instantiate this model. The following inputs need to be assigned:

- `Q_flow`, which is the heat flow rate added to the medium.
- `mWat_flow`, which is the moisture mass flow rate added to the medium.

Set the constant `sensibleOnly=true` if the model that extends or instantiates this model sets `mWat_flow = 0`.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
Boolean | sensibleOnly |  | Set to true if sensible exchange only
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate [kg/s]
Pressure | dp_nominal |  | Pressure difference [Pa]
Initialization
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
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
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed
Flow resistance
Boolean | computeFlowResistance | (abs(dp_nominal) > Modelica.... | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b)
output RealOutput | hOut | Leaving temperature of the component [J/kg]
output RealOutput | XiOut[Medium.nXi] | Leaving species concentration of the component [1]
output RealOutput | COut[Medium.nC] | Leaving trace substances of the component

### Modelica definition

model StaticTwoPortHeatMassExchanger "Partial model transporting fluid between two ports without storing mass or energy" extends Buildings.Fluid.Interfaces.PartialTwoPortInterface( showDesignFlowDirection = false); extends Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters( final computeFlowResistance=(abs(dp_nominal) > Modelica.Constants.eps)); parameter Boolean homotopyInitialization = true "= true, use homotopy method"; // Model inputs input Modelica.SIunits.HeatFlowRate Q_flow "Heat transferred into the medium"; input Modelica.SIunits.MassFlowRate mWat_flow "Moisture mass flow rate added to the medium"; // Models for conservation equations and pressure drop Buildings.Fluid.Interfaces.StaticTwoPortConservationEquation vol( sensibleOnly = sensibleOnly, use_safeDivision = use_safeDivision, redeclare final package Medium = Medium, final m_flow_nominal = m_flow_nominal, final allowFlowReversal=allowFlowReversal, final m_flow_small=m_flow_small) "Control volume for steady-state energy and mass balance"; Buildings.Fluid.FixedResistances.FixedResistanceDpM preDro( redeclare final package Medium = Medium, final use_dh=false, final m_flow_nominal=m_flow_nominal, final deltaM=deltaM, final allowFlowReversal=allowFlowReversal, final show_T=false, final from_dp=from_dp, final linearized=linearizeFlowResistance, final homotopyInitialization=homotopyInitialization, final dp_nominal=dp_nominal) "Pressure drop model"; // Outputs that are needed in models that extend this model Modelica.Blocks.Interfaces.RealOutput hOut(unit="J/kg") "Leaving temperature of the component"; Modelica.Blocks.Interfaces.RealOutput XiOut[Medium.nXi](each unit="1", each min=0, each max=1) "Leaving species concentration of the component"; Modelica.Blocks.Interfaces.RealOutput COut[Medium.nC](each min=0) "Leaving trace substances of the component"; constant Boolean sensibleOnly "Set to true if sensible exchange only"; constant Boolean use_safeDivision=true "Set to true to improve numerical robustness"; protected Modelica.Blocks.Sources.RealExpression heaInp(y=Q_flow) "Block to set heat input into volume"; Modelica.Blocks.Sources.RealExpression masExc(final y=mWat_flow) "Block to set moisture exchange in volume"; equation connect(vol.hOut, hOut); connect(vol.XiOut, XiOut); connect(vol.COut, COut); connect(port_a,preDro. port_a); connect(preDro.port_b, vol.port_a); connect(vol.port_b, port_b); connect(heaInp.y, vol.Q_flow); connect(masExc.y, vol.mWat_flow); end StaticTwoPortHeatMassExchanger;

## Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger

Partial model transporting one fluid stream with storing mass or energy

### Information

This component transports one fluid stream. It provides the basic model for implementing dynamic and steady-state models that exchange heat and water vapor with the fluid stream. The model also computes the pressure drop due to the flow resistance. By setting the parameter `dp_nominal=0`, the computation of the pressure drop can be avoided. The variable `vol.heatPort.T` always has the value of the temperature of the medium that leaves the component. For the actual temperatures at the port, the variables `sta_a.T` and `sta_b.T` can be used. These two variables are provided by the base class Buildings.Fluid.Interfaces.PartialTwoPortInterface.

For models that extend this model, see for example

- the ideal heater or cooler Buildings.Fluid.HeatExchangers.HeaterCooler_u, and
- the ideal humidifier Buildings.Fluid.MassExchangers.Humidifier_u.

#### Implementation

The variable names follow the conventions used in Modelica.Fluid.Examples.HeatExchanger.BaseClasses.BasicHX .

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
MixingVolume | vol | redeclare Buildings.Fluid.Mi... | Volume for fluid stream
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate [kg/s]
Pressure | dp_nominal |  | Pressure difference [Pa]
Initialization
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean | allowFlowReversal | true | = true to allow flow reversal, false restricts to design direction (port_a -> port_b)
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
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed
Flow resistance
Boolean | computeFlowResistance | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time | tau | 30 | Time constant at nominal flow (if energyDynamics <> SteadyState) [s]
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance
Dynamics | massDynamics | energyDynamics | Formulation of mass balance
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

### Modelica definition

model TwoPortHeatMassExchanger "Partial model transporting one fluid stream with storing mass or energy" extends Buildings.Fluid.Interfaces.PartialTwoPortInterface( port_a(h_outflow(start=h_outflow_start)), port_b(h_outflow(start=h_outflow_start))); extends Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters( final computeFlowResistance=true); parameter Modelica.SIunits.Time tau = 30 "Time constant at nominal flow (if energyDynamics <> SteadyState)"; // Advanced parameter Boolean homotopyInitialization = true "= true, use homotopy method"; // Dynamics parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial "Formulation of energy balance"; parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics "Formulation of mass balance"; // Initialization parameter Medium.AbsolutePressure p_start = Medium.p_default "Start value of pressure"; parameter Medium.Temperature T_start = Medium.T_default "Start value of temperature"; parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default "Start value of mass fractions m_i/m"; parameter Medium.ExtraProperty C_start[Medium.nC]( quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) "Start value of trace substances"; replaceable Buildings.Fluid.MixingVolumes.MixingVolume vol constrainedby Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume( redeclare final package Medium = Medium, nPorts = 2, V=m_flow_nominal*tau/rho_default, final mSenFac=1, final m_flow_nominal = m_flow_nominal, final energyDynamics=energyDynamics, final massDynamics=massDynamics, final p_start=p_start, final T_start=T_start, final X_start=X_start, final C_start=C_start) "Volume for fluid stream"; Buildings.Fluid.FixedResistances.FixedResistanceDpM preDro( redeclare final package Medium = Medium, final use_dh=false, final m_flow_nominal=m_flow_nominal, final deltaM=deltaM, final allowFlowReversal=allowFlowReversal, final show_T=false, final from_dp=from_dp, final linearized=linearizeFlowResistance, final homotopyInitialization=homotopyInitialization, final dp_nominal=dp_nominal) "Pressure drop model"; protected parameter Medium.ThermodynamicState sta_default=Medium.setState_pTX( T=Medium.T_default, p=Medium.p_default, X=Medium.X_default); parameter Modelica.SIunits.Density rho_default=Medium.density(sta_default) "Density, used to compute fluid volume"; parameter Medium.ThermodynamicState sta_start=Medium.setState_pTX( T=T_start, p=p_start, X=X_start); parameter Modelica.SIunits.SpecificEnthalpy h_outflow_start = Medium.specificEnthalpy(sta_start) "Start value for outflowing enthalpy"; initial algorithm assert((energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau > Modelica.Constants.eps, "The parameter tau, or the volume of the model from which tau may be derived, is unreasonably small. You need to set energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau = " + String(tau) + "\n"); assert((massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or tau > Modelica.Constants.eps, "The parameter tau, or the volume of the model from which tau may be derived, is unreasonably small. You need to set massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state. Received tau = " + String(tau) + "\n"); equation connect(vol.ports[2], port_b); connect(port_a, preDro.port_a); connect(preDro.port_b, vol.ports[1]); end TwoPortHeatMassExchanger;

## Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters

Parameters for flow resistance for models with four ports

### Information

This class contains parameters that are used to compute the pressure drop in components that have two fluid streams. Note that the nominal mass flow rate is not declared here because the model PartialFourPortInterface already declares it.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
Nominal condition
Pressure | dp1_nominal |  | Pressure difference [Pa]
Pressure | dp2_nominal |  | Pressure difference [Pa]
Flow resistance
Medium 1
Boolean | computeFlowResistance1 | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp1 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance1 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM1 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean | computeFlowResistance2 | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp2 | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance2 | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM2 | 0.1 | Fraction of nominal flow rate where flow transitions to laminar

### Modelica definition

record FourPortFlowResistanceParameters "Parameters for flow resistance for models with four ports" parameter Boolean computeFlowResistance1 = true "=true, compute flow resistance. Set to false to assume no friction"; parameter Boolean from_dp1 = false "= true, use m_flow = f(dp) else dp = f(m_flow)"; parameter Modelica.SIunits.Pressure dp1_nominal(min=0, displayUnit="Pa") "Pressure difference"; parameter Boolean linearizeFlowResistance1 = false "= true, use linear relation between m_flow and dp for any flow rate"; parameter Real deltaM1 = 0.1 "Fraction of nominal flow rate where flow transitions to laminar"; parameter Boolean computeFlowResistance2 = true "=true, compute flow resistance. Set to false to assume no friction"; parameter Boolean from_dp2 = false "= true, use m_flow = f(dp) else dp = f(m_flow)"; parameter Modelica.SIunits.Pressure dp2_nominal(min=0, displayUnit="Pa") "Pressure difference"; parameter Boolean linearizeFlowResistance2 = false "= true, use linear relation between m_flow and dp for any flow rate"; parameter Real deltaM2 = 0.1 "Fraction of nominal flow rate where flow transitions to laminar"; end FourPortFlowResistanceParameters;

## Buildings.Fluid.Interfaces.LumpedVolumeDeclarations

Declarations for lumped volumes

### Information

This class contains parameters and medium properties that are used in the lumped volume model, and in models that extend the lumped volume model.

These parameters are used by Buildings.Fluid.Interfaces.ConservationEquation, Buildings.Fluid.MixingVolumes.MixingVolume, Buildings.Rooms.MixedAir, and by Buildings.Rooms.BaseClasses.MixedAir.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | Modelica.Media.Interfaces.Pa... | Medium in the component
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
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.)

### Modelica definition

record LumpedVolumeDeclarations "Declarations for lumped volumes" replaceable package Medium = Modelica.Media.Interfaces.PartialMedium "Medium in the component"; // Assumptions parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial "Formulation of energy balance"; parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics "Formulation of mass balance"; final parameter Modelica.Fluid.Types.Dynamics substanceDynamics=energyDynamics "Formulation of substance balance"; final parameter Modelica.Fluid.Types.Dynamics traceDynamics=energyDynamics "Formulation of trace substance balance"; // Initialization parameter Medium.AbsolutePressure p_start = Medium.p_default "Start value of pressure"; parameter Medium.Temperature T_start=Medium.T_default "Start value of temperature"; parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default "Start value of mass fractions m_i/m"; parameter Medium.ExtraProperty C_start[Medium.nC]( quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) "Start value of trace substances"; parameter Medium.ExtraProperty C_nominal[Medium.nC]( quantity=Medium.extraPropertiesNames) = fill(1E-2, Medium.nC) "Nominal value of trace substances. (Set to typical order of magnitude.)"; parameter Real mSenFac(min=1)=1 "Factor for scaling the sensible thermal mass of the volume"; end LumpedVolumeDeclarations;

## Buildings.Fluid.Interfaces.PrescribedOutletStateParameters

Parameters for models with prescribed outlet state

### Information

This record declares parameters that are used by models with prescribed outlet temperature.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
HeatFlowRate | Q_flow_maxHeat | Modelica.Constants.inf | Maximum heat flow rate for heating (positive) [W]
HeatFlowRate | Q_flow_maxCool | -Modelica.Constants.inf | Maximum heat flow rate for cooling (negative) [W]
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate, used for regularization near zero flow [kg/s]
Dynamics
Time | tau | 10 | Time constant at nominal flow rate (used if energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState) [s]
Initialization
Temperature | T_start |  | Initial or guess value of set point [K]
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance

### Modelica definition

record PrescribedOutletStateParameters "Parameters for models with prescribed outlet state" parameter Modelica.SIunits.HeatFlowRate Q_flow_maxHeat = Modelica.Constants.inf "Maximum heat flow rate for heating (positive)"; parameter Modelica.SIunits.HeatFlowRate Q_flow_maxCool = -Modelica.Constants.inf "Maximum heat flow rate for cooling (negative)"; parameter Modelica.SIunits.MassFlowRate m_flow_nominal "Nominal mass flow rate, used for regularization near zero flow"; parameter Modelica.SIunits.Time tau(min=0) = 10 "Time constant at nominal flow rate (used if energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState)"; parameter Modelica.SIunits.Temperature T_start "Initial or guess value of set point"; parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.SteadyState "Formulation of energy balance"; end PrescribedOutletStateParameters;

## Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters

Parameters for flow resistance for models with two ports

### Information

This class contains parameters that are used to compute the pressure drop in models that have one fluid stream. Note that the nominal mass flow rate is not declared here because the model PartialTwoPortInterface already declares it.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
Nominal condition
Pressure | dp_nominal |  | Pressure difference [Pa]
Flow resistance
Boolean | computeFlowResistance | true | =true, compute flow resistance. Set to false to assume no friction
Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate
Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar

### Modelica definition

record TwoPortFlowResistanceParameters "Parameters for flow resistance for models with two ports" parameter Boolean computeFlowResistance = true "=true, compute flow resistance. Set to false to assume no friction"; parameter Boolean from_dp = false "= true, use m_flow = f(dp) else dp = f(m_flow)"; parameter Modelica.SIunits.Pressure dp_nominal(min=0, displayUnit="Pa") "Pressure difference"; parameter Boolean linearizeFlowResistance = false "= true, use linear relation between m_flow and dp for any flow rate"; parameter Real deltaM = 0.1 "Fraction of nominal flow rate where flow transitions to laminar"; end TwoPortFlowResistanceParameters;