This model describes the one-directional pressure driven
air flow through a crack-like opening, using the equation
V̇ = C Δpm,
V̇ is the volume flow rate,
C is a flow coefficient and
m is the flow exponent.
The flow coefficient is
C = L CD,Rat ΔpRat(0.5-m) (2/ρ0)0.5,
L is the effective air leakage area,
CD,Rat is the discharge coefficient at the reference condition,
ΔpRat 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 ΔpRat = 4 Pa and a discharge
coefficient of CD,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.
American Society of Heating, Refrigeration and Air-Conditioning
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,
- Michael Wetter. Multizone Airflow Model in Modelica. Proc. of the 5th International Modelica Conference, p. 431-440. Vienna, Austria, September 2006.
February 2, 2022, by Michael Wetter:
This is for
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:
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
which are not used by this model.
This change is non-backward compatible.
This is for
May 30, 2018, by Michael Wetter:
Improved documentation for
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).
January 22, 2016, by Michael Wetter:
Corrected type declaration of pressure difference.
October 8, 2013 by Michael Wetter:
Changed the parameter
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.
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