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.Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).
Package Content
Name  Description 

UsersGuide  User's Guide 
Coefficient_V_flow  Power law with coefficient for volume flow rate 
Coefficient_m_flow  Powerlaw with coefficient for mass flow rate 
DoorDiscretizedOpen  Door model using discretization along height coordinate 
DoorDiscretizedOperable  Door model using discretization along height coordinate 
DoorOpen  Door model for bidirectional air flow between rooms 
DoorOperable  Door model for bidirectional air flow between rooms that can be open or closed 
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 
Point_m_flow  Powerlaw with flow coeffient fitted based on flow exponent and 1 datapoint 
Points_m_flow  Powerlaw with flow coefficient and flow exponent fitted based on 2 datapoints 
Table_V_flow  Volume flow(yaxis) vs Pressure(xaxis) cubic spline fit model based on table data, with last two points linearly interpolated 
Table_m_flow  Mass flow(yaxis) vs Pressure(xaxis) cubic spline fit model based from table data, with last two points linearly interpolated 
ZonalFlow_ACS  Zonal flow with input air change per second 
ZonalFlow_m_flow  Zonal flow with input air change per second 
Types  Package with type definitions 
Examples  Collection of models that illustrate model use and test models 
Validation  Collection of validation models 
BaseClasses  Package with base classes for Buildings.Airflow.Multizone 
Buildings.Airflow.Multizone.Coefficient_V_flow
Power law with coefficient for volume flow rate
Information
This model describes the onedirectional pressure driven air flow through an opening, using the equation
V̇ = C Δp^{m},
where V̇ is the volume flow rate in m^{3}/s, C is a flow coefficient, Δp is the pressure difference in Pa, and m is the flow exponent.
A similar model is also used in the CONTAM software (Dols and Walton, 2015). 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 AirConditioning 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.
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.BaseClasses.PartialOneWayFlowElement (Partial model for flow resistance with oneway flow), Buildings.Airflow.Multizone.BaseClasses.PowerLawResistanceParameters (Power law resistance parameters).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  0.5  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  C  Flow coefficient, C = V_flow/ dp^m  
Nominal condition  
MassFlowRate  m_flow_nominal  rho_default*C*dp_turbulent  Nominal mass flow rate [kg/s] 
Custom Parameters  
MassFlowRate  m_flow  V_flow*rho  Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] 
VolumeFlowRate  V_flow  Buildings.Airflow.Multizone....  Volume flow rate through the component [m3/s] 
Advanced  
MassFlowRate  m_flow_small  1E4*abs(m_flow_nominal)  Small mass flow rate for regularization of zero flow [kg/s] 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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) 
Modelica definition
Buildings.Airflow.Multizone.Coefficient_m_flow
Powerlaw with coefficient for mass flow rate
Information
This model describes the onedirectional pressure driven air flow through an opening, using the equation
ṁ = k Δp^{m},
where ṁ is the mass flow rate in kg/s, k is a flow coefficient, Δp is the pressure difference in Pa, and m is the flow exponent.
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
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 AirConditioning 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. [1]
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.BaseClasses.PartialOneWayFlowElement (Partial model for flow resistance with oneway flow), Buildings.Airflow.Multizone.BaseClasses.PowerLawResistanceParameters (Power law resistance parameters).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  0.5  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  k  Flow coefficient, k = m_flow/ dp^m  
Nominal condition  
MassFlowRate  m_flow_nominal  k*dp_turbulent  Nominal mass flow rate [kg/s] 
Custom Parameters  
MassFlowRate  m_flow  rho*Buildings.Airflow.Multiz...  Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] 
Advanced  
MassFlowRate  m_flow_small  1E4*abs(m_flow_nominal)  Small mass flow rate for regularization of zero flow [kg/s] 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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) 
Modelica definition
Buildings.Airflow.Multizone.DoorDiscretizedOpen
Door model using discretization along height coordinate
Information
This model describes the bidirectional air flow through an open door.
To compute the bidirectional 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 

replaceable package Medium  PartialMedium  Medium in the component  
Velocity  vZer  0.001  Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s] 
Integer  nCom  10  Number of compartments for the discretization 
PressureDifference  dp_turbulent  0.01  Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [Pa] 
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 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
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
Buildings.Airflow.Multizone.DoorDiscretizedOperable
Door model using discretization along height coordinate
Information
This model describes the bidirectional air flow through an open door.
To compute the bidirectional 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.DoorDiscretizedOpen 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 

replaceable package Medium  PartialMedium  Medium in the component  
Velocity  vZer  0.001  Minimum velocity to prevent zero flow. Recommended: 0.001 [m/s] 
Integer  nCom  10  Number of compartments for the discretization 
PressureDifference  dp_turbulent  0.01  Pressure difference where laminar and turbulent flow relation coincide. Recommended: 0.01 [Pa] 
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] 
Rating conditions  
PressureDifference  dpCloRat  4  Pressure drop at rating condition of closed door [Pa] 
Real  CDCloRat  1  Discharge coefficient at rating conditions of closed door 
Closed door  
Area  LClo  Effective leakage area of closed door [m2]  
Real  CDClo  0.65  Discharge coefficient of closed door 
Real  mClo  0.65  Flow exponent for crack of closed door 
Open door  
Real  CDOpe  0.65  Discharge coefficient of open door 
Real  mOpe  0.5  Flow exponent for door of open door 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
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 [1] 
Modelica definition
Buildings.Airflow.Multizone.DoorOpen
Door model for bidirectional air flow between rooms
Information
Model for bidirectional air flow through a large opening such as a door.
In this model, the air flow is composed of two components, a onedirectional bulk air flow due to static pressure difference in the adjoining two thermal zones, and a twodirectional airflow due to temperatureinduced differences in density of the air in the two thermal zones. Although turbulent air flow is a nonlinear phenomenon, the model is based on the simplifying assumption that these two air flow rates can be superposed. (Superposition is only exact for laminar flow.) This assumption is made because it leads to a simple model and because there is significant uncertainty and assumptions anyway in such simplified a model for bidirectional flow through a door.
Main equations
The air flow rate due to static pressure difference is
V̇_{ab,p} = C_{D} w h (2/ρ_{0})^{0.5} Δp^{m},
where V̇ is the volumetric air flow rate, C_{D} is the discharge coefficient, w and h are the width and height of the opening, ρ_{0} is the mass density at the medium default pressure, temperature and humidity, m is the flow exponent and Δp = p_{a}  p_{b} is the static pressure difference between the thermal zones. For this model explanation, we will assume p_{a} > p_{b}. For turbulent flow, m=1/2 and for laminar flow m=1.
The air flow rate due to temperature difference in the thermal zones is V̇_{ab,t} for flow from thermal zone a to b, and V̇_{ba,t} for air flow rate from thermal zone b to a. The model has two air flow paths to allow bidirectional air flow. The mass flow rates at these two air flow paths are
ṁ_{a1} = ρ_{0} (+V̇_{ab,p}/2 + V̇_{ab,t}),
and, similarly,
V̇_{ba} = ρ_{0} (V̇_{ab,p}/2 + V̇_{ba,t}),
where we simplified the calculation by using the density ρ_{0}. To calculate V̇_{ba,t}, we again use the density ρ_{0} and because of this simplification, we can write
ṁ_{ab,t} = ṁ_{ba,t} = ρ_{0} V̇_{ab,t} = ρ_{0} V̇_{ba,t},
from which follows that the neutral height, e.g., the height where the air flow rate due to flow induced by temperature difference is zero, is at h/2. Hence,
V̇_{ab,t} = C_{D} ∫_{0}^{h/2} w v(z) dz,
where v(z) is the velocity at height z. From the Bernoulli equation, we obtain
v(z) = (2 g z Δρ ⁄ ρ_{0})^{1/2}.
The density difference can be written as
Δρ = ρ_{a}ρ_{b} ≈ ρ_{0} (T_{b}  T_{a}) ⁄ T_{0},
where we used ρ_{a} = p_{0} /(R T_{a}) and T_{a} T_{b} ≈ T_{0}^{2}. Substituting this expression into the integral and integrating from 0 to z yields
V̇_{ab,t} = 1⁄3 C_{D} w h (g h ⁄ (R T_{0} ρ_{0}))^{1/2} Δp^{1/2}.
The above equation is equivalent to (6) in Brown and Solvason (1962).
Main assumptions
The main assumptions are as follows:

The air flow rates due to static pressure difference and due to temperaturedifference can be superposed.

For buoyancydriven air flow, a constant density can be used to convert air volume flow rate to air mass flow rate.
From these assumptions follows that the neutral height for buoyancydriven air flow is at half of the height of the opening.
Notes
For a more detailed model, use Buildings.Airflow.Multizone.DoorDiscretizedOpen.
References

Brown, W.G. and K. R. Solvason.
Natural Convection through rectangular openings in partitions  1.
Int. Journal of Heat and Mass Transfer.
Vol. 5, p. 859868. 1962.
doi:10.1016/00179310(62)901849.
Also available at https://nrcpublications.canada.ca/eng/view/ft/?id=081c0ace7c31449c9b3be6c14864b196.
Extends from Buildings.Airflow.Multizone.BaseClasses.Door (Partial door model for bidirectional flow).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Geometry  
Length  wOpe  0.9  Width of opening [m] 
Length  hOpe  2.1  Height of opening [m] 
Custom Parameters  
Velocity  vAB  VAB_flow/AOpe  Average velocity from A to B [m/s] 
Velocity  vBA  VBA_flow/AOpe  Average velocity from B to A [m/s] 
Orifice characteristics  
Real  CD  0.65  Discharge coefficient 
Real  m  0.5  Flow coefficient 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
PressureDifference  dp_turbulent  0.01  Pressure difference where laminar and turbulent flow relation coincide [Pa] 
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
Buildings.Airflow.Multizone.DoorOperable
Door model for bidirectional air flow between rooms that can be open or closed
Information
Model for bidirectional air flow through a large opening such as a door which can be opened or closed based on the control input signal y.
For the control input signal y=1, this model is identical to Buildings.Airflow.Multizone.DoorOpen, and for y=0, the door is assumed to be closed and the air flow rate is set to the air flow rate through the crack posed by the open door, V̇_{clo}.
The air flow rate for the closed door is computed as
V̇_{clo} = C_{clo} Δp^{mClo},
where V̇_{clo} is the volume flow rate, C_{clo} is a flow coefficient and mClo is the flow exponent. The flow coefficient is
C_{clo} = L_{clo} C_{DCloRat} Δp_{Rat}^{(0.5mClo}) (2/ρ_{0})^{0.5},
where L_{clo} is the effective air leakage area, C_{DCloRat} is the discharge coefficient at the reference condition, Δp_{Rat} is the pressure drop at the rating condition, and ρ_{0} is the mass density at the medium default pressure, temperature and humidity.
The effective air leakage area L_{clo} 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 Δp_{Rat} = 4 Pa and a discharge coefficient of C_{DCloRat} = 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 mClo=0.6 to mClo=0.7 if the flow exponent is not reported with the test results.
For the open door, the air flow rate
V̇_{ope} is computed as described in
Buildings.Airflow.Multizone.DoorOpen
with the parameters CDOpe
and mOpe
.
The actual air flow rate is computed as
V̇_{clo} = (y1) V̇_{clo} + y V̇_{ope},
where y ∈ [0, 1] is the control signal. Note that for values of y that are different from 0 and 1, the model simply interpolates the air flow rate between a fully open and a fully closed door. In practice, the air flow rate would likely increase quickly if the door is slightly opened, and hence we do not claim that the model is accurate for values other than y = 0 and y = 1.
References
 ASHRAE. ASHRAE Fundamentals, American Society of Heating, Refrigeration and AirConditioning Engineers, 1997.
 Dols and Walton. 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.Door (Partial door model for bidirectional flow).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Geometry  
Length  wOpe  0.9  Width of opening [m] 
Length  hOpe  2.1  Height of opening [m] 
Custom Parameters  
Velocity  vAB  VAB_flow/A  Average velocity from A to B [m/s] 
Velocity  vBA  VBA_flow/A  Average velocity from B to A [m/s] 
Open door  
Real  CDOpe  0.65  Discharge coefficient of open door 
Real  mOpe  0.5  Flow exponent for door of open door 
Closed door  
Area  LClo  Effective leakage area of closed door [m2]  
Real  mClo  0.65  Flow exponent for crack of closed door 
Closed door rating conditions  
PressureDifference  dpCloRat  4  Pressure drop at rating condition of closed door [Pa] 
Real  CDCloRat  1  Discharge coefficient at rating conditions of closed door 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
PressureDifference  dp_turbulent  0.01  Pressure difference where laminar and turbulent flow relation coincide [Pa] 
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 [1] 
Modelica definition
Buildings.Airflow.Multizone.EffectiveAirLeakageArea
Effective air leakage area
Information
This model describes the onedirectional pressure driven air flow through a cracklike opening, using the equation
V̇ = C Δp^{m},
where V̇ is the volume flow rate, C is a flow coefficient and m is the flow exponent. The flow coefficient is
C = L C_{D,Rat} Δp_{Rat}^{(0.5m)} (2/ρ_{0})^{0.5},
where L is the effective air leakage area, C_{D,Rat} is the discharge coefficient at the reference condition, Δp_{Rat} is the pressure drop at the rating condition, and ρ_{0} is the mass density at the medium default pressure, temperature and humidity.
The effective air leakage area L 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 Δp_{Rat} = 4 Pa and a discharge coefficient of C_{D,Rat} = 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 AirConditioning 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.
 Michael Wetter. Multizone Airflow Model in Modelica. Proc. of the 5th International Modelica Conference, p. 431440. Vienna, Austria, September 2006.
Extends from Buildings.Airflow.Multizone.Coefficient_V_flow (Power law with coefficient for volume flow rate).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  0.65  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  C  L*CDRat*sqrt(2.0/rho_default...  Flow coefficient, C = V_flow/ dp^m 
Area  L  Effective leakage area [m2]  
Rating conditions  
PressureDifference  dpRat  4  Pressure drop [Pa] 
Real  CDRat  1  Discharge coefficient 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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
Buildings.Airflow.Multizone.MediumColumn
Vertical shaft with no friction and no storage of heat and mass
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.
Typical use and important parameters
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 toport_a
. 
bottom
: Use this setting to use the density from the volume that is connected toport_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.
Dynamics
For a dynamic model, use Buildings.Airflow.Multizone.MediumColumnDynamic instead of this model.
Parameters
Type  Name  Default  Description 

replaceable package Medium  Modelica.Media.Interfaces.Pa...  Medium in the component  
Length  h  3  Height of shaft [m] 
densitySelection  densitySelection  Select how to pick density 
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
Buildings.Airflow.Multizone.MediumColumnDynamic
Vertical shaft with no friction and storage of heat and mass
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.
Typical use and important parameters
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.
Dynamics
For a steadystate 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.
Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Length  h  3  Height of shaft [m] 
Volume  V  Volume in medium shaft [m3]  
Dynamics  
Conservation equations  
Dynamics  energyDynamics  Modelica.Fluid.Types.Dynamic...  Type of energy balance: dynamic (3 initialization options) or steady state 
Real  mSenFac  1  Factor for scaling the sensible thermal mass of the volume 
Advanced  
Dynamics  
Dynamics  massDynamics  energyDynamics  Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state 
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(1E2, Medium.nC)  Nominal value of trace substances. (Set to typical order of magnitude.) 
Assumptions  
Heat transfer  
Boolean  use_HeatTransfer  false  = true to use the HeatTransfer model 
replaceable model HeatTransfer  Modelica.Fluid.Vessels.BaseC...  Wall heat transfer 
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) 
HeatPort_a  heatPort  Heat port to exchange energy with the fluid volume 
Assumptions  
Heat transfer  
replaceable model HeatTransfer  Wall heat transfer 
Modelica definition
Buildings.Airflow.Multizone.Orifice
Orifice
Information
This model describes the mass flow rate and pressure difference relation of an orifice in the form
V̇ = C Δp^{m},
where V̇ is the volume flow rate, C is a flow coefficient and m is the flow exponent. The flow coefficient is
C = C_{D} A (2/ρ_{0})^{0.5},
where C_{D} is the discharge coefficient, A is the cross section area and ρ_{0} is the mass density at the medium default pressure, temperature and humidity.
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 cracklike 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.
 Michael Wetter. Multizone Airflow Model in Modelica. Proc. of the 5th International Modelica Conference, p. 431440. Vienna, Austria, September 2006.
Extends from Buildings.Airflow.Multizone.Coefficient_V_flow (Power law with coefficient for volume flow rate).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  0.5  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  C  CD*A*sqrt(2.0/rho_default)  Flow coefficient, C = V_flow/ dp^m 
Orifice characteristics  
Area  A  Area of orifice [m2]  
Real  CD  0.65  Discharge coefficient 
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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
Buildings.Airflow.Multizone.Point_m_flow
Powerlaw with flow coeffient fitted based on flow exponent and 1 datapoint
Information
Model that fits the flow coefficient of the massflow version of the orifice equation based on 1 datapoint of mass flow rate and pressure difference, and given flow exponent.
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
References
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.Coefficient_m_flow (Powerlaw with coefficient for mass flow rate).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  0.5  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  k  mMea_flow_nominal/(dpMea_nom...  Flow coefficient, k = m_flow/ dp^m 
Test data  
PressureDifference  dpMea_nominal  Pressure difference of test point [Pa]  
MassFlowRate  mMea_flow_nominal  Mass flow rate of test point [kg/s]  
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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
Buildings.Airflow.Multizone.Points_m_flow
Powerlaw with flow coefficient and flow exponent fitted based on 2 datapoints
Information
Model that fits the flow coefficient of the massflow version of the orifice equation based on 2 datapoints of mass flow rate and pressure difference.
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
References
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.Coefficient_m_flow (Powerlaw with coefficient for mass flow rate).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Real  m  m2  Flow exponent, m=0.5 for turbulent, m=1 for laminar 
Real  k  mMea_flow_nominal[1]/(dpMea_...  Flow coefficient, k = m_flow/ dp^m 
Test data  
PressureDifference  dpMea_nominal[2]  Pressure difference of two test points [Pa]  
MassFlowRate  mMea_flow_nominal[2]  Mass flow rate of two test points [kg/s]  
Advanced  
Diagnostics  
Boolean  show_T  false  = true, if actual temperature at port is computed 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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
Buildings.Airflow.Multizone.Table_V_flow
Volume flow(yaxis) vs Pressure(xaxis) cubic spline fit model based on table data, with last two points linearly interpolated
Information
This model describes the onedirectional pressure driven air flow through an opening based on userprovided tabular data describing the relation between volume flow rate and pressure difference over the component.
V̇ = f(Δp),
where V̇ is the volume flow rate and Δp is the pressure difference.
Based on the table input, a cubic hermite spline is constructed between all points except for the two last pairs of points. These point are connected linearly.
The constructed curve is the direct relation between V̇ and Δp.
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
References
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.Table_m_flow (Mass flow(yaxis) vs Pressure(xaxis) cubic spline fit model based from table data, with last two points linearly interpolated).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Test data  
PressureDifference  dpMea_nominal[:]  Pressure difference of test points [Pa]  
MassFlowRate  mMea_flow_nominal[:]  VMea_flow_nominal*rho_default  Mass flow rate of test points [kg/s] 
VolumeFlowRate  VMea_flow_nominal[:]  Volume flow rate of test points [m3/s]  
Advanced  
MassFlowRate  m_flow_small  1E4*abs(m_flow_nominal)  Small mass flow rate for regularization of zero flow [kg/s] 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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) 
Modelica definition
Buildings.Airflow.Multizone.Table_m_flow
Mass flow(yaxis) vs Pressure(xaxis) cubic spline fit model based from table data, with last two points linearly interpolated
Information
This model describes the onedirectional pressure driven air flow through an opening based on userprovided tabular data describing the relation between mass flow rate and pressure difference over the component.
ṁ = f(Δp),
where ṁ is the volume flow rate and Δp is the pressure difference.
Based on the table input, a cubic hermite spline is constructed between all points except for the two last pairs of points. These point are connected linearly.
The constructed curve is the direct relation between ṁ and Δp.
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
References
 W. S. Dols and B. J. Polidoro,2015. CONTAM User Guide and Program Documentation Version 3.2, National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi: 10.6028/NIST.TN.1887.
Extends from Buildings.Airflow.Multizone.BaseClasses.PartialOneWayFlowElement (Partial model for flow resistance with oneway flow).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Nominal condition  
MassFlowRate  m_flow_nominal  max(abs(dpMea_nominal[1]), a...  Nominal mass flow rate [kg/s] 
Custom Parameters  
MassFlowRate  m_flow  Buildings.Airflow.Multizone....  Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] 
Test data  
PressureDifference  dpMea_nominal[:]  Pressure difference of test points [Pa]  
MassFlowRate  mMea_flow_nominal[:]  Mass flow rate of test points [kg/s]  
Advanced  
MassFlowRate  m_flow_small  1E4*abs(m_flow_nominal)  Small mass flow rate for regularization of zero flow [kg/s] 
Boolean  forceErrorControlOnFlow  true  Flag to force error control on m_flow. Set to true if interested in flow rate 
Boolean  useDefaultProperties  true  Set to false to use density and viscosity based on actual medium state, rather than using default values 
PressureDifference  dp_turbulent  0.1  Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 [Pa] 
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) 
Modelica definition
Buildings.Airflow.Multizone.ZonalFlow_ACS
Zonal flow with input air change per second
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 

replaceable package Medium  PartialMedium  Medium in the component  
Boolean  useDefaultProperties  false  Set to true to use constant density 
Volume  V  Volume of room [m3]  
Advanced  
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) 
input RealInput  ACS  Air change per seconds, relative to the smaller of the two volumes 
Modelica definition
Buildings.Airflow.Multizone.ZonalFlow_m_flow
Zonal flow with input air change per second
Information
This model computes the air exchange between volumes.
Input is the mass flow rate from
port_a1
to port_b1
and from
port_a2
to port_b2
.
Extends from Buildings.Airflow.Multizone.BaseClasses.ZonalFlow (Flow across zonal boundaries of a room).
Parameters
Type  Name  Default  Description 

replaceable package Medium  PartialMedium  Medium in the component  
Advanced  
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) 
input RealInput  mAB_flow  Mass flow rate from A to B, positive if flow from port_a1 to port_b1 
input RealInput  mBA_flow  Mass flow rate from B to A, positive if flow from port_a2 to port_b2 