modelTwoWayFlowElement
Flow resistance that uses the power law
Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model with four ports and declaration of quantities that are used by many models), Buildings.Airflow.Multizone.BaseClasses.ErrorControl (Interface that defines parameters for error control).
Information
This is a partial model for models that describe the bi-directional air flow through large openings.
Models that extend this model need to compute
mAB_flow and mBA_flow,
or alternatively VAB_flow and VBA_flow,
and the face area area.
The face area is a variable to allow this partial model to be used
for doors that can be open or closed as a function of an input signal.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Velocity | vZer | 0.001 | Minimum velocity to prevent zero flow. Recommended: 0.001 |
| Assumptions | |||
| Boolean | allowFlowReversal1 (from PartialFourPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal for medium 1 |
| Boolean | allowFlowReversal2 (from PartialFourPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal for medium 2 |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate | m1_flow_nominal (from PartialFourPortInterface) | Nominal mass flow rate | |
| Modelica.Units.SI.MassFlowRate | m2_flow_nominal (from PartialFourPortInterface) | Nominal mass flow rate | |
| Advanced | |||
| Medium1.MassFlowRate | m1_flow_small (from PartialFourPortInterface) | 1E-4*abs(m1_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Medium2.MassFlowRate | m2_flow_small (from PartialFourPortInterface) | 1E-4*abs(m2_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Boolean | forceErrorControlOnFlow (from ErrorControl) | true | Flag to force error control on m_flow. Set to true if interested in flow rate |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialFourPortInterface) | false | = true, if actual temperature at port is computed |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPort_a | port_a1 (from PartialFourPort) | Fluid connector a1 (positive design flow direction is from port_a1 to port_b1) | |
| Modelica.Fluid.Interfaces.FluidPort_b | port_b1 (from PartialFourPort) | Fluid connector b1 (positive design flow direction is from port_a1 to port_b1) | |
| Modelica.Fluid.Interfaces.FluidPort_a | port_a2 (from PartialFourPort) | Fluid connector a2 (positive design flow direction is from port_a2 to port_b2) | |
| Modelica.Fluid.Interfaces.FluidPort_b | port_b2 (from PartialFourPort) | Fluid connector b2 (positive design flow direction is from port_a2 to port_b2) |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Medium1.MassFlowRate | m1_flow (from PartialFourPortInterface) | port_a1.m_flow | Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction) |
| Modelica.Units.SI.PressureDifference | dp1 (from PartialFourPortInterface) | port_a1.p - port_b1.p | Pressure difference between port_a1 and port_b1 |
| Medium2.MassFlowRate | m2_flow (from PartialFourPortInterface) | port_a2.m_flow | Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction) |
| Modelica.Units.SI.PressureDifference | dp2 (from PartialFourPortInterface) | port_a2.p - port_b2.p | Pressure difference between port_a2 and port_b2 |
| Medium1.ThermodynamicState | sta_a1 (from PartialFourPortInterface) | if allowFlowReversal1 then Medium1.setState_phX(port_a1.p, noEvent(actualStream(port_a1.h_outflow)), noEvent(actualStream(port_a1.Xi_outflow))) else Medium1.setState_phX(port_a1.p, inStream(port_a1.h_outflow), inStream(port_a1.Xi_outflow)) | Medium properties in port_a1 |
| Medium1.ThermodynamicState | sta_b1 (from PartialFourPortInterface) | if allowFlowReversal1 then Medium1.setState_phX(port_b1.p, noEvent(actualStream(port_b1.h_outflow)), noEvent(actualStream(port_b1.Xi_outflow))) else Medium1.setState_phX(port_b1.p, port_b1.h_outflow, port_b1.Xi_outflow) | Medium properties in port_b1 |
| Medium2.ThermodynamicState | sta_a2 (from PartialFourPortInterface) | if allowFlowReversal2 then Medium2.setState_phX(port_a2.p, noEvent(actualStream(port_a2.h_outflow)), noEvent(actualStream(port_a2.Xi_outflow))) else Medium2.setState_phX(port_a2.p, inStream(port_a2.h_outflow), inStream(port_a2.Xi_outflow)) | Medium properties in port_a2 |
| Medium2.ThermodynamicState | sta_b2 (from PartialFourPortInterface) | if allowFlowReversal2 then Medium2.setState_phX(port_b2.p, noEvent(actualStream(port_b2.h_outflow)), noEvent(actualStream(port_b2.Xi_outflow))) else Medium2.setState_phX(port_b2.p, port_b2.h_outflow, port_b2.Xi_outflow) | Medium properties in port_b2 |
| Modelica.Units.SI.VolumeFlowRate | VAB_flow | Volume flow rate from A to B if positive | |
| Modelica.Units.SI.VolumeFlowRate | VBA_flow | Volume flow rate from B to A if positive | |
| Modelica.Units.SI.MassFlowRate | mAB_flow | Mass flow rate from A to B if positive | |
| Modelica.Units.SI.MassFlowRate | mBA_flow | Mass flow rate from B to A if positive | |
| Modelica.Units.SI.Velocity | vAB | Average velocity from A to B | |
| Modelica.Units.SI.Velocity | vBA | Average velocity from B to A | |
| Modelica.Units.SI.Density | rho_a1_inflow | Density of air flowing in from port_a1 | |
| Modelica.Units.SI.Density | rho_a2_inflow | Density of air flowing in from port_a2 | |
| Modelica.Units.SI.Area | A | Face area |
Contents
| Name | Description |
|---|---|
 Medium | Medium in the component |
Revisions
-
September 22, 2025, by Michael Wetter:
Setunbounded=trueformExcAB_flowandmExcBA_flowto avoid spikes inport_a.m_flowin Buildings.Airflow.Multizone.Examples.OneOpenDoor.
This is for Buildings, #4360. -
September 19, 2025, by Michael Wetter:
Refactored implementation of underlying function that computes the flow rate to allow function to be inlined. This leads to a 20% faster simulation of Buildings.Airflow.Multizone.Examples.OneOpenDoor compared to the previous implementation.
This is for IBPSA, #2043. -
May 12, 2020, by Michael Wetter:
Changed assignment ofm1_flow_smallandm2_flow_smalltofinal. These quantities are not used in this model and models that extend from it. Hence there is no need for the user to change the value. -
January 18, 2019, by Jianjun Hu:
Limited the media choice to moist air only. See #1050. -
September 13, 2018, by Michael Wetter:
SetallowFlowReversal=trueas the flow can be slightly negative due to the regularization, in which case them_flow(min=0)that is set in the base class Buildings.Fluid.Interfaces.PartialFourPort is violated.
See #937. -
November 3, 2016, by Michael Wetter:
Removed start values for inflowing density to simplify the parameter window, and because this can usually be computed from the state variables.
This is for #552. -
February 24, 2015 by Michael Wetter:
Changed model to use Buildings.Utilities.Psychrometrics.Functions.density_pTX for the density computation as Buildings.Media.Air.density does not depend on temperature. - June 18, 2014 by Michael Wetter:
Added start values andfixed=trueattribute formExcABandmExcBA. This avoids a warning during translation. - July 20, 2010 by Michael Wetter:
Migrated model to Modelica 3.1 and integrated it into the Buildings library. - February 4, 2005 by Michael Wetter:
Released first version.