Having problems with message search?
Marco,
the Cp-value of -0.35 of the roof itself will be a good first indication for the Cp of the cowl.
The position on the roof is important, since Cp varies with the (horizontal) distance to the roof edge. Especially near the windward positioned roof edge a larger underpressure will be found.
Because of the cowl type a correction on Cp may be necessary. You can find these corrections in the AIVC Airbase article 2843, titled: Three investigations of the behaviour of ducts for natural ventilation (Drie onderzoeken naar de werking van kanalen voor natuurlijke ventilatie) by W.F. de Gids and H.P.L. den Ouden.
This article shows that relative Cp's of cowls very much depend on the cowl shape, the relation between outflow velocity and wind velocity as well as the local wind direction (both the horizontal and vertical flow angle).
It appears that only few cowl shapes give an approvement in relation to an open vertical duct outlet.
If you send me a picture of your cowl, I might provide you with the specific Cp-graph.
Regards,
Bas Knoll
ventilation expert
TNO Building and Construction Research
PO box 49
2600 AA Delft (NL)
phone +31 15 2763318
fax +31 15 2763023
mailto:B.Knoll@...
web http://www.tno.nl
-----Original Message-----
From: marco massetti [mailto:massetmar@...]
Sent: Wednesday, May 05, 2004 12:16 PM
To: comis
Subject: [comis] Cp cowlhelo,does any body know how to determinate the Cp value for a cowl at the top of a passive stack?the PS simulation is not active in COMIS,anyway I found at this position of the excel spreadsheet some default values sugested:Cp of the hood (cowl): -0.35z of the cowl: 2.5how have been determinated these values?is it corect to consider the cp value of the cowl constant and indipendent by its position on the roof (flat)? and indipendent by building geometry?I normally use CpCalc to calculate Cp values,but I sugest it's uncorrect to take the cp value of the roof and apply this to the cowl.thank you!marco massetti
Yahoo! Companion - Scarica gratis la toolbar di Ricerca di Yahoo!
To Post a message, send it to: comis@eGroups.com
To Unsubscribe, send a blank message to: comis-unsubscribe@eGroups.com
Offline 
Send Email