[EnergyPlus_Support] Re: Simulating double skin facade

["lorenzomattarolo" <lorenzomattarolo@xxxxxxxx>]

>From your suggestion I understood that maybe the natural vented model
is not correct to describe the double facade.
Can you suggest me how to model the facade in an appropriate way?

I give you some basic information of the facade:

- naturally ventilated with inlet and outlet openings every 2 floors
- gap width of 2,7 m 
- shading louvres in the gap close to the internal skin

I tried considering the double facade as a separate zone and using the
airflownetwork model.
However I found some basic limitation.
For istance shading blnds can't stay at a distance more than 1 meter
from the external skin.
Moreover airflownetwork can't model correctly the stratification of
the air.

Many thanks,

Lorenzo





--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Griffith, Brent"
<brent_griffith@...> wrote:
>
> If I understand you right, I think what you are actually getting in the
> model is a regular window surrounded by a wall with a double skin.  See
> if the inside face wall surface temperatures are different.  The window
> shouldn't be changing.  
> 
>  
> 
> The exterior vented cavity model assumes all the solar is blocked by a
> thin, solid layer on the outside and cannot be used for glazing.  Opaque
> means no transmission.  Inside E+ this becomes a special boundary
> condition for surface heat transfer modeling that is not available for
> window modeling.  The window still gets exterior environment bc even
> though its parent surface has the exterior cavity bc. 
> 
>  
> 
> Double facade improvements are being planned for the future.  
> 
>  
> 
> I suppose if you really wanted to use the exterior vented cavity model
> on your DF, it could apply to a case where the double facade has totally
> opaque shades that are closed tight.  You would use regular materials in
> the construction for the surface that approximate the DF (no subsurface
> and no glazing materials).  The baffle in the exterior cavity model can
> get quite hot and then reradiate infrared (but no shortwave) and convect
> to the underlying surface.  But note that air gap models are much better
> developed for windows that for regular constructions; you would have to
> come up with thermal properties for each layer.  One advantage of this
> approach might be a better model of transient behavior because the
> window models are always steady state.




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