.Buildings.Airflow.Multizone.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/ρ₀)^0.5,

where C_D is the discharge coefficient, A is the cross section area and ρ₀ 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 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.
• Michael Wetter. Multizone Airflow Model in Modelica. Proc. of the 5th International Modelica Conference, p. 431-440. Vienna, Austria, September 2006.

Revisions

• February 2, 2022, by Michael Wetter:
  Revised implementation.
  This is for IBPSA, #1436.
• Apr 6, 2021, by Klaas De Jonge:
  Changes due to changes in the baseclass, velocity is now a top-level variable.
• June 27, 2018, by Michael Wetter:
  Corrected old parameter annotation.
• June 24, 2018, by Michael Wetter:
  Removed parameter lWet as it is only used to compute the Reynolds number, and the Reynolds number is not used by this model. Also removed the variable Re for the Reynolds number.
  This change is non-backward compatible.
  This is for IBPSA, #932.
• May 30, 2018, by Michael Wetter:
  Improved documentation for IBPSA, #546.
• October 8, 2013 by Michael Wetter:
  Changed the parameter useConstantDensity to useDefaultProperties to use consistent names within this package. A conversion script can be used to update this parameter.
• December 6, 2011 by Michael Wetter:
  Replaced rho with rho_nominal because rho is computed in an equation section and not in the initial equation section.
• 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.