Hi Marcello,
If you supply 0.1 m/s through the floor (as experiment in your mind) that would
lead to about 133 ACH if the room is 2.7 m high.
So 28 is possible far within reasonable air speeds.
Summer ventilation of busses could go up to 400 ACH.
Try to estimate the "ACH" if you walk outdoor.

Note that Comis as far as I know , needs a split up of a single window in a room
in two half windows with a difference in cp to get a wind influence at single
sided ventilation.
Air flows in and out through a single open window would be in the order of 0.5
m/s at shielded buildings (not the high rise buildings) and normal
wind/temperature differences.

You could estimate the jet behind a window with handbook jet equations (Awbi
etc), and maybe limit to 0.5 to 1 m/s in summer.
Succes, hans phaff

>>-----Original Message-----
>>From: comis@yahoogroups.com [mailto:comis@yahoogroups.com] On
>>Behalf Of Marcello
>>Sent: Wednesday, June 04, 2008 10:10 AM
>>To: comis@yahoogroups.com
>>Subject: [comis] Air speed in natural ventilation
>>
>>Dear Comis users,
>>
>>I am doing some calculations to estimate the potential of
>>cooling by natural ventilation during mid seasons in offices.
>>I have some orders of magnitude about the ACH that I need in
>>a building, and they are in the order of 28.
>>
>>I wonder if it is possible to have such a value of ACH by
>>natural ventilation. Theorically, if I size my openings for
>>this airflow, I obtain that with all my glazed surfaces (50%
>>of the façade) opened I can reach 28 ACH (single-side
>>bouyancy-driven ventilation, deltaT 3 K). Simulating these
>>openings with COMIS, I obtain as well similar values of ACH.
>>However, it seems to me that it is not very reasonable that
>>with all the windows opened occupants can feel good,
>>expecially in offices. I imagine that with 28 ACH there is
>>wind into the building!!!
>>
>>Thus, I would like to know if someone know some limiting
>>value of ACH by windows opening or have some equations to
>>calculate the air speed and then limiting it.
>>
>>Thank you very much for any help!
>>
>>Marcello Caciolo
>>Ecole des Mines de Paris
>>marcello.caciolo@...
>>
>>
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