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Hi Marco
* The passive stack function was removed from the COMIS 3.1 kernel, because it wasn't working properly in version 3.0. However, a passive stack can also be modelled simply as vertical duct (DS component). But in this case, the dependencence of pressure loss or gain on the ratio of air velocity in the duct and wind velocity is not taken into account. Nevertheless, this should hopefully not cause great inaccuracy.
* The optional parameter Zeta is the dynamic loss coefficient (0.0 to 1.0 per fitting) for additional duct fittings, i.e. it should be used in cases where you have any additional pressure loss components over and above the one duct fitting already specified in the DS component. COMIS will thus add this "Zeta" to the zeta value for the one duct fitting type already specified in the three right-most columns. The default is 0. In your specific case, you should therefore specify Zeta for the second duct component (cowl or grille). Appropriate zeta values are given in ASHRAE Fundamentals (as "Local loss coefficients", C).
* You can very simply model many components in series by summating their Zeta values, and specifying this in one DS component. Note: if the nominal cross sectional area of a duct component differs from the duct cross sectional area, you may in some cases have to correct the the Zeta values for the change in flow area -- see ASHRAE Fundamentals about how to do this.
* Zeta should not be confused with the friction of the duct itself. COMIS calculates the duct friction based on the duct dimensions and length that you specify.
Good luck!
--
Dr.ing. Peter G. Schild
Norwegian Building Research Institute
P.O.box 123 Blindern, N-0314 Oslo, Norway
Phone: (+47) 22 965 854
(Please note that NBI does not regard e-mail correspondence as legally binding)
Dr.ing. Peter G. Schild
Norwegian Building Research Institute
P.O.box 123 Blindern, N-0314 Oslo, Norway
Phone: (+47) 22 965 854
(Please note that NBI does not regard e-mail correspondence as legally binding)
Fra: marco massetti
Sendt: fr 2004-04-02 20:08
Til: comis
Emne: [comis] PS simulation
hallo,
I need to simulate a passive stack, but this header is not implemented by the comis version I use;
so I'm trying with a duct and 2 duct fittings (a Cowl at the top and a grille at the base).
That means a distributed pressure loss and 2 concentrated pressure losses.
some questions about it:
- which is the meaning of Zeta coeff. in ducts?
isn't enought for comis to know diameter(1/2) and Roughness for friction coeff. calculation?
- how can I apply the duct fittings to the duct? or put these air flow elements in serie?
- can I have more informations about duct fittings and their parameters?
I need to simulate a passive stack, but this header is not implemented by the comis version I use;
so I'm trying with a duct and 2 duct fittings (a Cowl at the top and a grille at the base).
That means a distributed pressure loss and 2 concentrated pressure losses.
some questions about it:
- which is the meaning of Zeta coeff. in ducts?
isn't enought for comis to know diameter(1/2) and Roughness for friction coeff. calculation?
- how can I apply the duct fittings to the duct? or put these air flow elements in serie?
- can I have more informations about duct fittings and their parameters?
I hope somebody can help me,
thank you for your patience!
thank you for your patience!
marco massetti,
politecnico di torino
politecnico di torino
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