Buildings.Airflow.Multizone

Package with models for multizone airflow and contaminant transport

Information

This package provides models to compute the airflow and contaminant transport between different rooms and between a room and the exterior environment. See the User's Guide for more information.

Package Content

Name Description

UsersGuide User's Guide

DoorDiscretizedOpen Door model using discretization along height coordinate

DoorDiscretizedOperable Door model using discretization along height coordinate

EffectiveAirLeakageArea Effective air leakage area

MediumColumn Vertical shaft with no friction and no storage of heat and mass

MediumColumnDynamic Vertical shaft with no friction and storage of heat and mass

Orifice Orifice

ZonalFlow_ACS Zonal flow with input air change per second

ZonalFlow_m_flow Zonal flow with input air change per second

Examples Package with example models

BaseClasses Package with base classes for multizone airflow models

Types Package with type definitions

Name	Description
UsersGuide	User's Guide
DoorDiscretizedOpen	Door model using discretization along height coordinate
DoorDiscretizedOperable	Door model using discretization along height coordinate
EffectiveAirLeakageArea	Effective air leakage area
MediumColumn	Vertical shaft with no friction and no storage of heat and mass
MediumColumnDynamic	Vertical shaft with no friction and storage of heat and mass
Orifice	Orifice
ZonalFlow_ACS	Zonal flow with input air change per second
ZonalFlow_m_flow	Zonal flow with input air change per second
Examples	Package with example models
BaseClasses	Package with base classes for multizone airflow models
Types	Package with type definitions

Buildings.Airflow.Multizone.DoorDiscretizedOpen

Door model using discretization along height coordinate

Buildings.Airflow.Multizone.DoorDiscretizedOpen

Information

This model describes the bi-directional air flow through an open door.

To compute the bi-directional flow, the door is discretize along the height coordinate. An orifice equation is used to compute the flow for each compartment.

In this model, the door is always open. Use the model Buildings.Airflow.Multizone.DoorDiscretizedOperable for a door that can either be open or closed.

Extends from Buildings.Airflow.Multizone.BaseClasses.DoorDiscretized (Door model using discretization along height coordinate).

Parameters

Type Name Default Description

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

replaceable package Medium PartialMedium

Velocity vZer 0.001 Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s]

Integer nCom 10 Number of compartments for the discretization

Pressure dp_turbulent 0.01 Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [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]

Density rho_a1_inflow.start 1.2 Density of air flowing in from port_a1 [kg/m3]

Density rho_a2_inflow.start 1.2 Density of air flowing in from port_a2 [kg/m3]

Geometry

Length wOpe 0.9 Width of opening [m]

Length hOpe 2.1 Height of opening [m]

Length hA 2.7/2 Height of reference pressure zone A [m]

Length hB 2.7/2 Height of reference pressure zone B [m]

Orifice characteristics

Real CD 0.65 Discharge coefficient

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]

Advanced

MassFlowRate m1_flow_small 1E-4*m1_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

MassFlowRate m2_flow_small 1E-4*m2_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

Diagnostics

Boolean show_V_flow false = true, if volume flow rate at inflowing port is computed

Boolean show_T false = true, if actual temperature at port is computed (may lead to events)

Type	Name	Default	Description
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
replaceable package Medium	PartialMedium
Velocity	vZer	0.001	Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s]
Integer	nCom	10	Number of compartments for the discretization
Pressure	dp_turbulent	0.01	Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [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]
Density	rho_a1_inflow.start	1.2	Density of air flowing in from port_a1 [kg/m3]
Density	rho_a2_inflow.start	1.2	Density of air flowing in from port_a2 [kg/m3]
Geometry
Length	wOpe	0.9	Width of opening [m]
Length	hOpe	2.1	Height of opening [m]
Length	hA	2.7/2	Height of reference pressure zone A [m]
Length	hB	2.7/2	Height of reference pressure zone B [m]
Orifice characteristics
Real	CD	0.65	Discharge coefficient
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]
Advanced
MassFlowRate	m1_flow_small	1E-4*m1_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*m2_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

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)

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 DoorDiscretizedOpen 
  "Door model using discretization along height coordinate"
  extends Buildings.Airflow.Multizone.BaseClasses.DoorDiscretized;

equation 
  m=0.5;
  A = wOpe*hOpe;
  kVal = CD*dA*sqrt(2/rhoAve);
end DoorDiscretizedOpen;

Buildings.Airflow.Multizone.DoorDiscretizedOperable

Door model using discretization along height coordinate

Buildings.Airflow.Multizone.DoorDiscretizedOperable

Information

This model describes the bi-directional air flow through an open door.

To compute the bi-directional flow, the door is discretize along the height coordinate, and uses an orifice equation to compute the flow for each compartment.

The door can be either open or closed, depending on the input signal y. Set y=0 if the door is closed, and y=1 if the door is open. Use the model Buildings.Airflow.Multizone.Crack for a door that is always closed.

Extends from Buildings.Airflow.Multizone.BaseClasses.DoorDiscretized (Door model using discretization along height coordinate).

Parameters

Type Name Default Description

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

replaceable package Medium PartialMedium

Velocity vZer 0.001 Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s]

Integer nCom 10 Number of compartments for the discretization

Pressure dp_turbulent 0.01 Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [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]

Density rho_a1_inflow.start 1.2 Density of air flowing in from port_a1 [kg/m3]

Density rho_a2_inflow.start 1.2 Density of air flowing in from port_a2 [kg/m3]

Geometry

Length wOpe 0.9 Width of opening [m]

Length hOpe 2.1 Height of opening [m]

Length hA 2.7/2 Height of reference pressure zone A [m]

Length hB 2.7/2 Height of reference pressure zone B [m]

Orifice characteristics

Real CD 0.65 Discharge coefficient

Closed aperture rating conditions

Pressure dpCloRat 4 Pressure drop at rating condition [Pa]

Real CDCloRat 1 Discharge coefficient

Closed aperture

Area LClo Effective leakage area [m2]

Real CDClo 0.65 Discharge coefficient

Real mClo 0.65 Flow exponent for crack

Open aperture

Real CDOpe 0.65 Discharge coefficient

Real mOpe 0.5 Flow exponent for door

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]

Advanced

MassFlowRate m1_flow_small 1E-4*m1_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

MassFlowRate m2_flow_small 1E-4*m2_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

Diagnostics

Boolean show_V_flow false = true, if volume flow rate at inflowing port is computed

Boolean show_T false = true, if actual temperature at port is computed (may lead to events)

Type	Name	Default	Description
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
replaceable package Medium	PartialMedium
Velocity	vZer	0.001	Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s]
Integer	nCom	10	Number of compartments for the discretization
Pressure	dp_turbulent	0.01	Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [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]
Density	rho_a1_inflow.start	1.2	Density of air flowing in from port_a1 [kg/m3]
Density	rho_a2_inflow.start	1.2	Density of air flowing in from port_a2 [kg/m3]
Geometry
Length	wOpe	0.9	Width of opening [m]
Length	hOpe	2.1	Height of opening [m]
Length	hA	2.7/2	Height of reference pressure zone A [m]
Length	hB	2.7/2	Height of reference pressure zone B [m]
Orifice characteristics
Real	CD	0.65	Discharge coefficient
Closed aperture rating conditions
Pressure	dpCloRat	4	Pressure drop at rating condition [Pa]
Real	CDCloRat	1	Discharge coefficient
Closed aperture
Area	LClo		Effective leakage area [m2]
Real	CDClo	0.65	Discharge coefficient
Real	mClo	0.65	Flow exponent for crack
Open aperture
Real	CDOpe	0.65	Discharge coefficient
Real	mOpe	0.5	Flow exponent for door
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]
Advanced
MassFlowRate	m1_flow_small	1E-4*m1_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*m2_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

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)
input RealInput	y	Opening signal, 0=closed, 1=open

Modelica definition

model DoorDiscretizedOperable 
  "Door model using discretization along height coordinate"
  extends Buildings.Airflow.Multizone.BaseClasses.DoorDiscretized;

   parameter Modelica.SIunits.Pressure dpCloRat(min=0)=4 
    "|Closed aperture rating conditions|Pressure drop at rating condition";
  parameter Real CDCloRat(min=0, max=1)=1 
    "|Closed aperture rating conditions|Discharge coefficient";

  parameter Modelica.SIunits.Area LClo(min=0) 
    "|Closed aperture|Effective leakage area";

  parameter Real CDOpe=0.65 "|Open aperture|Discharge coefficient";
  parameter Real CDClo=0.65 "|Closed aperture|Discharge coefficient";

  parameter Real mOpe = 0.5 "|Open aperture|Flow exponent for door";
  parameter Real mClo= 0.65 "|Closed aperture|Flow exponent for crack";
  Modelica.Blocks.Interfaces.RealInput y "Opening signal, 0=closed, 1=open";
protected 
 parameter Modelica.SIunits.Area AOpe=wOpe*hOpe "Open aperture area";
 parameter Modelica.SIunits.Area AClo(fixed=false) "Closed aperture area";

 Real kOpe "Open aperture flow coefficient, k = V_flow/ dp^m";
 Real kClo "Closed aperture flow coefficient, k = V_flow/ dp^m";

 Real fraOpe "Fraction of aperture that is open";
initial equation 
  AClo=CDClo/CDCloRat * LClo * dpCloRat^(0.5-mClo);
equation 
  assert(y           >= 0, "Input error. Opening signal must be between 0 and 1.\n"
    + "  Received y.signal[1] = " + realString(y));
  assert(y           <= 1, "Input error. Opening signal must be between 0 and 1.\n"
    + "  Received y.signal[1] = " + realString(y));
  fraOpe =y;
  kClo = CDClo * AClo/nCom * sqrt(2/rhoAve);
  kOpe = CDOpe * AOpe/nCom * sqrt(2/rhoAve);

  // flow exponent
  m    = fraOpe*mOpe + (1-fraOpe)*mClo;
  // opening area
  A = fraOpe*AOpe + (1-fraOpe)*AClo;
  // friction coefficient for power law
  kVal = fraOpe*kOpe + (1-fraOpe)*kClo;
end DoorDiscretizedOperable;

Buildings.Airflow.Multizone.EffectiveAirLeakageArea

Effective air leakage area

Buildings.Airflow.Multizone.EffectiveAirLeakageArea

Information

This model describes the one-directional pressure driven air flow through a crack-like opening.

The opening is modeled as an orifice. The orifice area is parameterized by processing the effective air leakage area, the discharge coefficient and pressure drop at a reference condition. The effective air leakage area can be obtained, for example, from the ASHRAE fundamentals (ASHRAE, 1997, p. 25.18). In the ASHRAE fundamentals, the effective air leakage area is based on a reference pressure difference of 4 Pa and a discharge coefficient of 1. A similar model is also used in the CONTAM software (Dols and Walton, 2002). Dols and Walton (2002) recommend to use for the flow exponent m=0.6 to m=0.7 if the flow exponent is not reported with the test results.

References

ASHRAE, 1997. ASHRAE Fundamentals, American Society of Heating, Refrigeration and Air-Conditioning Engineers, 1997.
Dols and Walton, 2002. W. Stuart Dols and George N. Walton, CONTAMW 2.0 User Manual, Multizone Airflow and Contaminant Transport Analysis Software, Building and Fire Research Laboratory, National Institute of Standards and Technology, Tech. Report NISTIR 6921, November, 2002.

Extends from Buildings.Airflow.Multizone.Orifice (Orifice).

Parameters

Type Name Default Description

replaceable package Medium PartialMedium Medium in the component

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

Real m 0.65 Flow exponent, m=0.5 for turbulent, m=1 for laminar

Boolean useConstantDensity true Set to false to use density based on state (as implemented by the Medium model)

Pressure dp_turbulent 0.1 Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa]

Length lWet sqrt(A) Wetted perimeter used for Reynolds number calculation [m]

Area L Effective leakage area [m2]

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]

Orifice characteristics

Area A CD/CDRat*L*dpRat^(0.5 - m) Area of orifice [m2]

Real CD 0.65 Discharge coefficient

Rating conditions

Pressure dpRat 4 Pressure drop at rating condition [Pa]

Real CDRat 1 Discharge coefficient

Assumptions

Boolean allowFlowReversal system.allowFlowReversal = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

Advanced

MassFlowRate m_flow_small 1E-4*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 (may lead to events)

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
Real	m	0.65	Flow exponent, m=0.5 for turbulent, m=1 for laminar
Boolean	useConstantDensity	true	Set to false to use density based on state (as implemented by the Medium model)
Pressure	dp_turbulent	0.1	Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa]
Length	lWet	sqrt(A)	Wetted perimeter used for Reynolds number calculation [m]
Area	L		Effective leakage area [m2]
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]
Orifice characteristics
Area	A	CD/CDRatLdpRat^(0.5 - m)	Area of orifice [m2]
Real	CD	0.65	Discharge coefficient
Rating conditions
Pressure	dpRat	4	Pressure drop at rating condition [Pa]
Real	CDRat	1	Discharge coefficient
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*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 (may lead to events)

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)

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

model EffectiveAirLeakageArea "Effective air leakage area"
  extends Buildings.Airflow.Multizone.Orifice(
     m=0.65, final A=CD/CDRat * L * dpRat^(0.5-m));

  parameter Modelica.SIunits.Pressure dpRat(min=0)=4 
    "|Rating conditions|Pressure drop at rating condition";
  parameter Real CDRat(min=0, max=1)=1 
    "|Rating conditions|Discharge coefficient";

  parameter Modelica.SIunits.Area L(min=0) "Effective leakage area";

end EffectiveAirLeakageArea;

Buildings.Airflow.Multizone.MediumColumn

Vertical shaft with no friction and no storage of heat and mass

Buildings.Airflow.Multizone.MediumColumn

Information

This model describes the pressure difference of a vertical medium column. It can be used to model the pressure difference caused by stack effect.

The model can be used with the following three configurations, which are controlled by the setting of the parameter densitySelection:

top: Use this setting to use the density from the volume that is connected to port_a.
bottom: Use this setting to use the density from the volume that is connected to port_b.
actual: Use this setting to use the density based on the actual flow direction.

The settings top and bottom should be used when rooms or different floors of a building are connected since multizone airflow models assume that each floor is completely mixed. For these two seetings, this model will compute the pressure between the center of the room and an opening that is at height h relative to the center of the room. The setting actual may be used to model a chimney in which a column of air will change its density based on the flow direction.

In this model, the parameter h must always be positive, and the port port_a must be at the top of the column.

For a steady-state model, use Buildings.Airflow.Multizone.MediumColumnDynamic instead of this model.

Parameters

Type Name Default Description

Length h 3 Height of shaft [m]

densitySelection densitySelection Select how to pick density

Assumptions

Boolean allowFlowReversal system.allowFlowReversal = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

Type	Name	Default	Description
Length	h	3	Height of shaft [m]
densitySelection	densitySelection		Select how to pick density
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)

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

model MediumColumn 
  "Vertical shaft with no friction and no storage of heat and mass"
  import Modelica.Constants;
  outer Modelica.Fluid.System system "System wide properties";

  replaceable package Medium = Modelica.Media.Interfaces.PartialMedium 
    "Medium in the component";

  parameter Modelica.SIunits.Length h(min=0) = 3 "Height of shaft";
  parameter Buildings.Airflow.Multizone.Types.densitySelection densitySelection
    "Select how to pick density";
  parameter Boolean allowFlowReversal=system.allowFlowReversal 
    "= true to allow flow reversal, false restricts to design direction (port_a -> port_b)";

  Modelica.Fluid.Interfaces.FluidPort_a port_a(
    redeclare package Medium = Medium,
    m_flow(min=if allowFlowReversal then -Constants.inf else 0),
    p(start=Medium.p_default, nominal=Medium.p_default)) 
    "Fluid connector a (positive design flow direction is from port_a to port_b)";
  Modelica.Fluid.Interfaces.FluidPort_b port_b(
    redeclare package Medium = Medium,
    m_flow(max=if allowFlowReversal then +Constants.inf else 0),
    p(start=Medium.p_default, nominal=Medium.p_default)) 
    "Fluid connector b (positive design flow direction is from port_a to port_b)";

  Modelica.SIunits.VolumeFlowRate V_flow=m_flow/Medium.density(sta_a) 
    "Volume flow rate at inflowing port (positive when flow from port_a to port_b)";
  Medium.MassFlowRate m_flow(start=0) 
    "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";
  Modelica.SIunits.Density rho "Density in medium column";
protected 
  Medium.ThermodynamicState sta_a=Medium.setState_phX(
      port_a.p,
      actualStream(port_a.h_outflow),
      actualStream(port_a.Xi_outflow)) "Medium properties in port_a";
initial equation 
  assert(abs(Medium.density(Medium.setState_pTX(
    Medium.p_default,
    Medium.T_default,
    Medium.X_default)) - Medium.density(Medium.setState_pTX(
    Medium.p_default,
    Medium.T_default + 5,
    Medium.X_default))) > 1E-10,
    "Error: The density of the medium that is used to compute buoyancy force is independent of temperature."
     + "\n       You need to select a different medium model.");
  assert(densitySelection > 0,
    "You need to set the parameter \"densitySelection\" for the model MediumColumn.");
equation 
  // Design direction of mass flow rate
  m_flow = port_a.m_flow;

  // Pressure difference between ports
  rho = if (densitySelection == Buildings.Airflow.Multizone.Types.densitySelection.fromTop) then 
          Medium.density(Medium.setState_phX(
    port_a.p,
    inStream(port_a.h_outflow),
    inStream(port_a.Xi_outflow))) else if (densitySelection == Buildings.Airflow.Multizone.Types.densitySelection.fromBottom) then 
          Medium.density(Medium.setState_phX(
    port_b.p,
    inStream(port_b.h_outflow),
    inStream(port_b.Xi_outflow))) else Medium.density(Medium.setState_phX(
    port_a.p,
    actualStream(port_a.h_outflow),
    actualStream(port_a.Xi_outflow)));
  dp = port_a.p - port_b.p;
  dp = -h*rho*Modelica.Constants.g_n;

  // Isenthalpic state transformation (no storage and no loss of energy)
  port_a.h_outflow = inStream(port_b.h_outflow);
  port_b.h_outflow = inStream(port_a.h_outflow);

  // 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 MediumColumn;

Buildings.Airflow.Multizone.MediumColumnDynamic

Vertical shaft with no friction and storage of heat and mass

Buildings.Airflow.Multizone.MediumColumnDynamic

Information

This model contains a completely mixed fluid volume and models that take into account the pressure difference of a medium column that is at the same temperature as the fluid volume. It can be used to model the pressure difference caused by a stack effect.

Set the parameter use_HeatTransfer=true to expose a heatPort. This heatPort can be used to add or subtract heat from the volume. This allows, for example, to use this model in conjunction with a model for heat transfer through walls to model a solar chimney that stores heat.

For a steady-state model, use Buildings.Airflow.Multizone.MediumColumn instead of this model.

In this model, the parameter h must always be positive, and the port port_a must be at the top of the column.

Parameters

Type Name Default Description

Length h 3 Height of shaft [m]

Volume V Volume in medium shaft [m3]

Assumptions

Boolean allowFlowReversal system.allowFlowReversal = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

Dynamics

Dynamics energyDynamics system.energyDynamics Formulation of energy balance

Dynamics massDynamics system.massDynamics Formulation of mass balance

Dynamics substanceDynamics energyDynamics Formulation of substance balance

Dynamics traceDynamics energyDynamics Formulation of trace substance balance

Heat transfer

Boolean use_HeatTransfer false = true to use the HeatTransfer model

Initialization

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 system.T... Start value of temperature [K]

SpecificEnthalpy h_start if use_T_start then Medium.s... Start value of specific enthalpy [J/kg]

MassFraction X_start[Medium.nX] Medium.X_default Start value of mass fractions m_i/m [kg/kg]

ExtraProperty C_start[Medium.nC] fill(0, Medium.nC) Start value of trace substances

Type	Name	Default	Description
Length	h	3	Height of shaft [m]
Volume	V		Volume in medium shaft [m3]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Dynamics	substanceDynamics	energyDynamics	Formulation of substance balance
Dynamics	traceDynamics	energyDynamics	Formulation of trace substance balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
Initialization
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 system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances

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)
HeatPort_a	heatPort

Modelica definition

model MediumColumnDynamic 
  "Vertical shaft with no friction and storage of heat and mass"
  import Modelica.Constants;
  outer Modelica.Fluid.System system "System wide properties";

  replaceable package Medium = Modelica.Media.Interfaces.PartialMedium 
    "Medium in the component";

  parameter Modelica.SIunits.Length h(min=0) = 3 "Height of shaft";
  parameter Boolean allowFlowReversal=system.allowFlowReversal 
    "= true to allow flow reversal, false restricts to design direction (port_a -> port_b)";

  Modelica.Fluid.Interfaces.FluidPort_a port_a(
    redeclare package Medium = Medium,
    m_flow(min=if allowFlowReversal then -Constants.inf else 0),
    p(start=Medium.p_default, nominal=Medium.p_default)) 
    "Fluid connector a (positive design flow direction is from port_a to port_b)";
  Modelica.Fluid.Interfaces.FluidPort_b port_b(
    redeclare package Medium = Medium,
    m_flow(max=if allowFlowReversal then +Constants.inf else 0),
    p(start=Medium.p_default, nominal=Medium.p_default)) 
    "Fluid connector b (positive design flow direction is from port_a to port_b)";

  Fluid.MixingVolumes.MixingVolume vol(
    final nPorts=2,
    redeclare final package Medium = Medium,
    final V=V,
    final energyDynamics=energyDynamics,
    final massDynamics=massDynamics,
    final substanceDynamics=substanceDynamics,
    final traceDynamics=traceDynamics,
    final p_start=p_start,
    final use_T_start=use_T_start,
    final T_start=T_start,
    final h_start=h_start,
    final X_start=X_start,
    final C_start=C_start,
    final use_HeatTransfer=use_HeatTransfer,
    redeclare final model HeatTransfer = HeatTransfer) 
    "Air volume in the shaft";

  MediumColumn colTop(
    redeclare final package Medium = Medium,
    final densitySelection=Buildings.Airflow.Multizone.Types.densitySelection.fromBottom,
    h=h/2,
    final allowFlowReversal=allowFlowReversal) 
    "Medium column that connects to top port";

  MediumColumn colBot(
    redeclare final package Medium = Medium,
    final densitySelection=Buildings.Airflow.Multizone.Types.densitySelection.fromTop,
    h=h/2,
    final allowFlowReversal=allowFlowReversal) 
    "Medium colum that connects to bottom port";

  parameter Modelica.SIunits.Volume V "Volume in medium shaft";

  // Assumptions
  parameter Modelica.Fluid.Types.Dynamics energyDynamics=system.energyDynamics 
    "Formulation of energy balance";
  parameter Modelica.Fluid.Types.Dynamics massDynamics=system.massDynamics 
    "Formulation of mass balance";
  parameter Modelica.Fluid.Types.Dynamics substanceDynamics=energyDynamics 
    "Formulation of substance balance";
  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 Boolean use_T_start = true "= true, use T_start, otherwise h_start";
  parameter Medium.Temperature T_start=
    if use_T_start then system.T_start else Medium.temperature_phX(p_start,h_start,X_start) 
    "Start value of temperature";
  parameter Medium.SpecificEnthalpy h_start=
    if use_T_start then Medium.specificEnthalpy_pTX(p_start, T_start, X_start) else Medium.h_default 
    "Start value of specific enthalpy";
  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";

  // Heat transfer through boundary
  parameter Boolean use_HeatTransfer = false 
    "= true to use the HeatTransfer model";
  replaceable model HeatTransfer =
      Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.IdealHeatTransfer
    constrainedby 
    Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.PartialVesselHeatTransfer 
    "Wall heat transfer";
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort if use_HeatTransfer;

equation 
  connect(colBot.port_a, vol.ports[1]);
  connect(vol.ports[2], colTop.port_b);
  connect(colTop.port_a, port_a);

  connect(colBot.port_b, port_b);
  connect(heatPort, vol.heatPort);

end MediumColumnDynamic;

Buildings.Airflow.Multizone.Orifice

Orifice

Buildings.Airflow.Multizone.Orifice

Information

This model describes the mass flow rate and pressure difference relation of an orifice in the form

    V_flow = k * dp^m,

where k is a variable and m a parameter. For turbulent flow, set m=1/2 and for laminar flow, set m=1. Large openings are characterized by values close to 0.5, while values near 0.65 have been found for small crack-like openings (Dols and Walton, 2002).

References

W. Stuart Dols and George N. Walton, CONTAMW 2.0 User Manual, Multizone Airflow and Contaminant Transport Analysis Software, Building and Fire Research Laboratory, National Institute of Standards and Technology, Tech. Report NISTIR 6921, November, 2002.

Extends from Buildings.Airflow.Multizone.BaseClasses.PowerLawResistance (Flow resistance that uses the power law).

Parameters

Type Name Default Description

replaceable package Medium PartialMedium Medium in the component

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

Real m 0.5 Flow exponent, m=0.5 for turbulent, m=1 for laminar

Boolean useConstantDensity true Set to false to use density based on state (as implemented by the Medium model)

Pressure dp_turbulent 0.1 Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa]

Length lWet sqrt(A) Wetted perimeter used for Reynolds number calculation [m]

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]

Orifice characteristics

Area A Area of orifice [m2]

Real CD 0.65 Discharge coefficient

Assumptions

Boolean allowFlowReversal system.allowFlowReversal = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

Advanced

MassFlowRate m_flow_small 1E-4*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 (may lead to events)

Type	Name	Default	Description
replaceable package Medium	PartialMedium	Medium in the component
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
Real	m	0.5	Flow exponent, m=0.5 for turbulent, m=1 for laminar
Boolean	useConstantDensity	true	Set to false to use density based on state (as implemented by the Medium model)
Pressure	dp_turbulent	0.1	Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa]
Length	lWet	sqrt(A)	Wetted perimeter used for Reynolds number calculation [m]
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]
Orifice characteristics
Area	A		Area of orifice [m2]
Real	CD	0.65	Discharge coefficient
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*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 (may lead to events)

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

model Orifice "Orifice"
  extends Buildings.Airflow.Multizone.BaseClasses.PowerLawResistance(m=0.5);

  parameter Real CD=0.65 "|Orifice characteristics|Discharge coefficient";
protected 
  parameter Real coef = CD * A * sqrt(2.0) "Constant coefficient";

initial equation 
  k = coef / sqrt(rho);
end Orifice;

Buildings.Airflow.Multizone.ZonalFlow_ACS

Zonal flow with input air change per second

Buildings.Airflow.Multizone.ZonalFlow_ACS

Information

This model computes the air exchange between volumes.

Input is the air change per seconds. The volume flow rate is computed as

  V_flow = ACS * V

where ACS is an input and the volume V is a parameter.

Extends from Buildings.Airflow.Multizone.BaseClasses.ZonalFlow (Flow across zonal boundaries of a room).

Parameters

Type Name Default Description

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

replaceable package Medium PartialMedium

Boolean useConstantDensity false Set to true to use constant density

Volume V Volume of room [m3]

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]

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]

Advanced

MassFlowRate m1_flow_small 1E-4*m1_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

MassFlowRate m2_flow_small 1E-4*m2_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

Diagnostics

Boolean show_V_flow false = true, if volume flow rate at inflowing port is computed

Boolean show_T false = true, if actual temperature at port is computed (may lead to events)

Type	Name	Default	Description
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
replaceable package Medium	PartialMedium
Boolean	useConstantDensity	false	Set to true to use constant density
Volume	V		Volume of room [m3]
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]
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]
Advanced
MassFlowRate	m1_flow_small	1E-4*m1_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*m2_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

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)
input RealInput	ACS	Air change per seconds, relative to the smaller of the two volumes

Modelica definition

model ZonalFlow_ACS "Zonal flow with input air change per second"
  extends Buildings.Airflow.Multizone.BaseClasses.ZonalFlow;

  parameter Boolean useConstantDensity = false 
    "Set to true to use constant density";
  parameter Modelica.SIunits.Volume V "Volume of room";

  Modelica.Blocks.Interfaces.RealInput ACS 
    "Air change per seconds, relative to the smaller of the two volumes";
protected 
  Modelica.SIunits.VolumeFlowRate V_flow 
    "Volume flow rate at standard pressure";
  Modelica.SIunits.MassFlowRate m_flow "Mass flow rate";
  parameter Medium.ThermodynamicState sta0 = Medium.setState_pTX(T=Medium.T_default,
         p=Medium.p_default, X=Medium.X_default);
  parameter Modelica.SIunits.Density rho_nominal=Medium.density(sta0) 
    "Density, used to compute fluid volume";

  Medium.ThermodynamicState sta_a1_inflow=
      Medium1.setState_phX(port_a1.p, port_b1.h_outflow, port_b1.Xi_outflow) 
    "Medium properties in port_a1";
  Medium.ThermodynamicState sta_a2_inflow=
      Medium1.setState_phX(port_a2.p, port_b2.h_outflow, port_b2.Xi_outflow) 
    "Medium properties in port_a2";

equation 
  when useConstantDensity and initial() then
   assert( abs(1-rho_nominal/((Medium.density(sta_a1_inflow) + Medium.density(sta_a2_inflow))/2))  < 0.2,
    "Wrong density. Densities need to match."
    + "\n Medium.density(sta_a1) = " + realString(Medium.density(sta_a1_inflow))
    + "\n Medium.density(sta_a2) = " + realString(Medium.density(sta_a2_inflow))
    + "\n rho_nominal            = " + realString(rho_nominal));
  end when;
  V_flow = V * ACS;
  m_flow / V_flow = if useConstantDensity then rho_nominal else (Medium.density(sta_a1_inflow) + Medium.density(sta_a2_inflow))/2;
  // assign variable in base class
  port_a1.m_flow = m_flow;
  port_a2.m_flow = m_flow;
end ZonalFlow_ACS;

Buildings.Airflow.Multizone.ZonalFlow_m_flow

Zonal flow with input air change per second

Buildings.Airflow.Multizone.ZonalFlow_m_flow

Information

This model computes the air exchange between volumes.

Input is the mass flow rate from A to B and from B to A.

Extends from Buildings.Airflow.Multizone.BaseClasses.ZonalFlow (Flow across zonal boundaries of a room).

Parameters

Type Name Default Description

Boolean forceErrorControlOnFlow true Flag to force error control on m_flow. Set to true if interested in flow rate

replaceable package Medium PartialMedium

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]

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]

Advanced

MassFlowRate m1_flow_small 1E-4*m1_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

MassFlowRate m2_flow_small 1E-4*m2_flow_nominal Small mass flow rate for regularization of zero flow [kg/s]

Diagnostics

Boolean show_V_flow false = true, if volume flow rate at inflowing port is computed

Boolean show_T false = true, if actual temperature at port is computed (may lead to events)

Type	Name	Default	Description
Boolean	forceErrorControlOnFlow	true	Flag to force error control on m_flow. Set to true if interested in flow rate
replaceable package Medium	PartialMedium
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]
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]
Advanced
MassFlowRate	m1_flow_small	1E-4*m1_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*m2_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

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)
input RealInput	mAB_flow	Mass flow rate from A to B
input RealInput	mBA_flow	Mass flow rate from B to A

Modelica definition

model ZonalFlow_m_flow "Zonal flow with input air change per second"
  extends Buildings.Airflow.Multizone.BaseClasses.ZonalFlow;
   Modelica.Blocks.Interfaces.RealInput mAB_flow "Mass flow rate from A to B";
  Modelica.Blocks.Interfaces.RealInput mBA_flow "Mass flow rate from B to A";

equation 
  port_a1.m_flow = mAB_flow;
  port_a2.m_flow = mBA_flow;

end ZonalFlow_m_flow;

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