RE: [EnergyPlus_Support] Re: Simulating double skin facade

["Griffith, Brent" <brent_griffith@xxxxxxxx>]

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.

 

 

 

________________________________

From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of
lorenzomattarolo
Sent: Monday, August 06, 2007 10:01 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Simulating double skin facade

 

Thanks for your answer.

I compared two simulation, one with the facade as exterior vented
cavity and the other with the facade as a simple window, and it seems
that solar transmission through the glazing system is the same in both
the cases.

Even if the exterior vented cavity is only for opaque surfaces do you
think it is possible to use the model for a glass facade, using as
input (thermal emissivity and solar absorbtivity) the data of the
glazing system?
Which differences or errors would occur using that model?

Lorenzo

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> , "Griffith, Brent"
<brent_griffith@...> wrote:
>
> The exterior vented natural cavity model is for *opaque* surfaces only
> and does not apply to glazing systems. 
> 
> 
> 
> There is a model for blinds in the window gap that takes those two
> things into account, but I am not sure if it works together with the
air
> flow window model. 
> 
> 
> 
> 
> 
> 
> 
> ________________________________
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> 
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of
> lorenzomattarolo
> Sent: Monday, August 06, 2007 7:48 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> 
> Subject: [EnergyPlus_Support] Simulating double skin facade
> 
> 
> 
> Hi,
> I'm simulating an office with a double skin facade using the "exterior
> vented natural cavity".
> The facade is naturally ventilated and it has venetian blinds in the
> gap.
> 
> The blinds are exposed to the solar radiation and they can reach
> during the day very high temperatures, which can affect 
> 1. the temperature of the air in the gap
> 2. the performance of the glass facade
> 
> Does EnergyPlus take into account these two effects?
> 
> Thanks for your help and your suggestion,
> 
> Lorenzo
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]
>

 



[Non-text portions of this message have been removed]



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