modelMediumColumn

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

Dynamics

For a dynamic model, use Buildings.Airflow.Multizone.MediumColumnDynamic instead of this model.

Parameters

TypeNameDefaultDescription
Modelica.Units.SI.Lengthh3Height of shaft
Buildings.Airflow.Multizone.Types.densitySelectiondensitySelectionSelect how to pick density

Connectors

TypeNameDefaultDescription
Modelica.Fluid.Interfaces.FluidPort_aport_aFluid connector a (positive design flow direction is from port_a to port_b)
Modelica.Fluid.Interfaces.FluidPort_bport_bFluid connector b (positive design flow direction is from port_a to port_b)

Components

TypeNameDefaultDescription
Modelica.Units.SI.VolumeFlowRateV_flowVolume flow rate at inflowing port (positive when flow from port_a to port_b)
Modelica.Units.SI.MassFlowRatem_flowMass flow rate from port_a to port_b (m_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifferencedpPressure difference between port_a and port_b
Modelica.Units.SI.DensityrhoDensity in medium column

Contents

NameDescription
MediumMedium in the component

Revisions

  • January 18, 2019, by Jianjun Hu:
    Limited the media choice to moist air only. See #1050.
  • May 1, 2018, by Filip Jorissen:
    Removed declaration of allowFlowReversal and changed default density computation such that it assumes a constant pressure. See #877.
  • November 3, 2016, by Michael Wetter:
    Removed start values for mass flow rate and pressure difference to simplify the parameter window.
    This is for #552.
  • January 22, 2016, by Michael Wetter:
    Corrected type declaration of pressure difference. This is for #404.
  • 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.
  • December 22, 2014 by Michael Wetter:
    Removed Modelica.Fluid.System to address issue #311.
  • October 4, 2014 by Michael Wetter:
    Removed assignment of port_?.p.nominal to avoid a warning in OpenModelica because alias sets have different nominal values.
  • April 17, 2013 by Michael Wetter:
    Reformulated the assert statement that checks for the correct value of densitySelection.
  • July 28, 2010 by Michael Wetter:
    Changed sign for pressure difference.
  • July 20, 2010 by Michael Wetter:
    Migrated model to Modelica 3.1 and integrated it into the Buildings library. Reimplemented assignment of density based on flow direction or based on outflowing state.
  • February 24, 2005 by Michael Wetter:
    Released first version.