Buildings.Fluids.MixingVolumes

Package Content

Name	Description
BaseClasses	Package with base classes for mixing volumes
MixingVolume	Mixing volume with inlet and outlet ports (flow reversal is allowed)
MixingVolumeDryAir	Mixing volume with heat port for latent heat exchange, to be used with dry air
MixingVolumeMoistAir	Mixing volume with heat port for latent heat exchange, to be used with media that conatin water

Buildings.Fluids.MixingVolumes.MixingVolume

Information

This model represents the same physics as Modelica_Fluid.Volumes.MixingVolume, but it allows to have more than two fluid ports. This is convenient for modeling the room volume in a building energy simulation since rooms often have more than two fluid connections, such as an HVAC inlet, outlet and a leakage flow to other rooms or the outside. If a fluid port is connected twice, the model will terminate the simulation with an error message.

The thermal port need not be connected, but can have any number of connections.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Integer	nP	2	Number of ports
Boolean	steadyState	false	Set to true for steady state model
Initialization
Temp	initType	Types.Init.NoInit	Initialization option
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then Medium.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]

Connectors

Type	Name	Description
FluidPort_a	port[nP]	Fluid port
HeatPort_a	thermalPort	Thermal port

Modelica definition

model MixingVolume 
  "Mixing volume with inlet and outlet ports (flow reversal is allowed)" 
  extends BaseClasses.PartialMixingVolume;
  
equation 
// Mass and energy balance 
  if steadyState then
    0 = sum(port[i].m_flow for i in 1:nP);
    zeros(Medium.nXi) = sum(port[i].mXi_flow for i in 1:nP);
    0 = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow;
  else
    der(m) = sum(port[i].m_flow for i in 1:nP);
    der(mXi) = sum(port[i].mXi_flow for i in 1:nP);
    der(U) = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow;
  end if;
  
 //  /* der(m) */ 0 = sum(port[i].m_flow for i in 1:nP);
 //  /* der(mXi) */ zeros(Medium.nXi) = sum(port[i].mXi_flow for i in 1:nP);
 //  /* der(U) */ 0 = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow;
end MixingVolume;

Buildings.Fluids.MixingVolumes.MixingVolumeDryAir

Information

This model represents the same physics as Buildings.Fluids.MixingVolumes.MixingVolume, but in addition, it allows adding (or subtracting) water in liquid phase, which causes a change in enthalpy and species concentration. The water flow rate is assumed to be added or extracted at the temperature of the input port TWat, or if this port is not connected at the medium default temperature as returned by Medium.T_default.

Note that this model can only be used with medium models that include water as a substance. In particular, the medium model need to provide the function enthalpyOfLiquid(T) and the integer variable Water that contains the index to the water substance. For medium that do not provide this functionality, use instead the model Buildings.Fluids.MixingVolumes.MixingVolumeDryAir.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Integer	nP	2	Number of ports
Boolean	steadyState	false	Set to true for steady state model
Initialization
Temp	initType	Types.Init.NoInit	Initialization option
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then Medium.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]

Connectors

Type	Name	Description
FluidPort_a	port[nP]	Fluid port
HeatPort_a	thermalPort	Thermal port
input RealInput	mWat_flow	Water flow rate added into the medium
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume
output RealOutput	XWat	Species composition of medium

Modelica definition

model MixingVolumeDryAir 
  "Mixing volume with heat port for latent heat exchange, to be used with dry air" 
  extends BaseClasses.PartialMixingVolumeWaterPort;
  
equation 
  if cardinality(mWat_flow) == 0 then
    mWat_flow = 0;
  end if;
  if cardinality(TWat) == 0 then
    TWat = Medium.T_default;
  end if;
  HWat_flow = 0;
  mXi_flow  = zeros(Medium.nXi);
// Assign output port
  XWat = 0;
end MixingVolumeDryAir;

Buildings.Fluids.MixingVolumes.MixingVolumeMoistAir

Information

This model represents the same physics as Buildings.Fluids.MixingVolumes.MixingVolume, but in addition, it allows adding (or subtracting) water in liquid phase, which causes a change in enthalpy and species concentration. The water flow rate is assumed to be added or extracted at the temperature of the input port TWat, or if this port is not connected at the medium default temperature as returned by Medium.T_default.

Note that this model can only be used with medium models that include water as a substance. In particular, the medium model need to provide the function enthalpyOfLiquid(T) and the integer variable Water that contains the index to the water substance. For medium that do not provide this functionality, use instead the model Buildings.Fluids.MixingVolumes.MixingVolumeDryAir.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Integer	nP	2	Number of ports
Boolean	steadyState	false	Set to true for steady state model
Initialization
Temp	initType	Types.Init.NoInit	Initialization option
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then Medium.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]

Connectors

Type	Name	Description
FluidPort_a	port[nP]	Fluid port
HeatPort_a	thermalPort	Thermal port
input RealInput	mWat_flow	Water flow rate added into the medium
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume
output RealOutput	XWat	Species composition of medium

Modelica definition

model MixingVolumeMoistAir 
  "Mixing volume with heat port for latent heat exchange, to be used with media that conatin water" 
  extends BaseClasses.PartialMixingVolumeWaterPort;
  // redeclare Medium with a more restricting base class. This improves the error
  // message if a user selects a medium that does not contain the function
  // enthalpyOfLiquid(.)
  replaceable package Medium = Modelica.Media.Interfaces.PartialCondensingGases;
  
equation 
  if cardinality(mWat_flow) == 0 then
    mWat_flow = 0;
    HWat_flow = 0;
    mXi_flow  = zeros(Medium.nXi);
  else
    if cardinality(TWat) == 0 then
       HWat_flow = mWat_flow * Medium.enthalpyOfLiquid(Medium.T_default);
    else
       HWat_flow = mWat_flow * Medium.enthalpyOfLiquid(TWat);
    end if;
    for i in 1:Medium.nXi loop
      mXi_flow[i] = if ( i == Medium.Water) then mWat_flow else 0;
    end for;
  end if;
// Medium species concentration
  XWat = medium.X[Medium.Water];
end MixingVolumeMoistAir;