AixLib.Airflow.Multizone.BaseClasses.TwoWayFlowElement

# .AixLib.Airflow.Multizone.BaseClasses.TwoWayFlowElement

Flow resistance that uses the power law

## 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.

## Contents

Name | Description
--- | ---
Medium | Medium in the component

## Revisions

- May 12, 2020, by Michael Wetter:
  Changed assignment of `m1_flow_small` and `m2_flow_small` to `final`. 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:
  Set `allowFlowReversal=true` as the flow can be slightly negative due to the regularization, in which case the `m_flow(min=0)` that is set in the base class AixLib.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 and `fixed=true` attribute for `mExcAB` and `mExcBA`. 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.

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