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[EnergyPlus_Support] Re: Natural ventilation through horizontal openings_AirflowNetwork

Hi,

Did you see the following note in the Input/Output Reference under detailed opening?

"The AirflowNetwork model does not have a model for bi-directional flow through large horizontal openings. For this reason, AirflowNetwork:MultiZone:Component:DetailedOpening should not be used for horizontal openings. The best modeling technique in this case is to put an AirflowNetwork:MultiZone:Surface:Crack object in a horizontal surface and use a large air mass flow coefficient. Crack flow is assumed to be uni-directional in any given timestep (but
can reverse flow direction from timestep to timestep)."

I've never tried using a crack to represent a horizontal window. It seems like you might run into the problem that the crack isn't operable like the actual horizontal window is, so you will get really large exfiltration rates at times when the window should be closed.

Let us know how it goes!

Sam


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@...> wrote:
>
> Good question. The horizontal opening is designed for interlevel openings like stairwells (see engineering ref.). I think the reason why roof cracks are mainly ignored is because most infiltration is wind driven and when the wind flows over the roof it mainly creates a negative pressure which may result in small amounts of exfiltration. Exfiltration is usually not as interesting as infiltration. The best article I've seen dealing with the "infiltration" of buildings is:
> 
> http://ibpsa-boston.com/minutes/IBPSAboston-presentations_2011-09-16_Gowri.pdf
> 
> I'm trying to come up with a good infiltration methodology for a sawtooth roofed factory. The large factory hall in nestled inside other buildings and basically only the roof is exterior surface which peaks out about 2 m above all else. The aspect ratio of the hall gives it a large volume to exterior surface area relationship.
> 150 x 90 x 12 m
> 
> Let us know what you learn.
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Vaibhav Jain <vaibhav.energyarchitect@> wrote:
> >
> > Hello everyone!
> > 
> > I am trying to understand natural ventilation through AirflowNetwork. The
> > model is a simple single storied model, with a periphery and a core zone.
> > The periphery zone has several vertical windows; and the central core zone
> > has only one horizontal window on its roof.
> > 
> > As per the IO reference - the AirflowNetwork model, in
> > AirflowNetwork:MultiZone:Component:SimpleOpening and
> > AirflowNetwork:MultiZone:Component:DetailedOpening, assumes openings to be
> > vertical or close to vertical, this is good in case of vertical windows in
> > periphery zone. That also means that the horizontal window in the core zone
> > cannot be defined with these field. So then I
> > tried AirflowNetwork:MultiZone:Component:HorizontalOpening for the
> > horizontal window, but, the IO reference says that this field assumes
> > openings to be - horizontal or close to horizontal AND AN INTERZONE
> > SURFACE.
> > 
> > So my question is: how can we define AirflowNetwork for outside viewing
> > horizontal windows, which are not INTERZONE SURFACES (for eg. a horizontal
> > skylight with openings)?  OR we simply cannot define it for such openings?
> > 
> > I hope the query is comprehensible. Thank you!
> > 
> > Best regards,
> > Vaibhav Jain
> > www.vaibhavjain.co
> >
>




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