.BuildingSystems.Airflow.Multizone.EffectiveAirLeakageArea

Information

This model describes the one-directional pressure driven air flow through a crack-like 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^(0.5-m) (2/ρ₀)^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 ρ₀ 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 Air-Conditioning 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. 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 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.
  Changed base class to remove the parameters A and CD which are not used by this model.
  This change is non-backward compatible.
  This is for IBPSA, #932.
• May 30, 2018, by Michael Wetter:
  Improved documentation for IBPSA, #546.
• April 24, 2017, by Filip Jorissen:
  Corrected error in computation of A which was A=CD/CDRat * L * dpRat^(0.5-m) rather than A=CDRat/CD * L * dpRat^(0.5-m).
  See #743.
• January 22, 2016, by Michael Wetter:
  Corrected type declaration of pressure difference. This is for #404.
• 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.
• July 20, 2010 by Michael Wetter:
  Migrated model to Modelica 3.1 and integrated it into the Buildings library.
• February 10, 2005 by Michael Wetter:
  Released first version.