[Bldg-sim] Is there a quick model for double skins facades?

[Marques da Silva]

Hi Peter

I think you are only considering DSF gap forced ventilation (/when the 
air system was switched off after occupation?/). This not an issue is 
it's naturally ventilated. My opinion, and I am not a designer but I've 
been monitoring a few occupied DSF façades in the warm climate of 
Lisbon, is that as for any other building system it has to be properly 
designed having in mind location and use. I monitored really bad façades 
but also façades that behave quite well allowing the interior 
temperature to remain within comfort levels during weekends when HVAC is 
switched off.
I don't know ROOM but TRNSYS is a good option for modelling DSF (see the 
work of Haase et al).
I agree that cold climates are preferable when considering a DSF option, 
but there are other issues like, for example, tall and wind exposed 
façades, specially if  glazzed, where inside shading is thermally a bad 
option and for outside positioning fast damage is certain. Anyway owners 
may allways impose a look for their building...
>
> Nick and Vikram, double skin facades or climate walls or windows have 
> been around for many years now. Vikram's question is really how do you 
> produce a back of the envelope calculation to see if a double skin 
> façade is a viable option. Well here goes, the basic improvement by 
> using a double façade is the improvement of the U value decreasing 
> energy loss. Take a look around the world and the successful 
> applications of double facades is mostly in regions where heating is 
> the dominant energy consumer. One of the first things were learnt more 
> than 30 years ago was the U value was improved so long as air was 
> ventilated through the cavity, but what happened to the U value when 
> the air system was switched off after occupation? which consumed more 
> energy, the energy loss of the building without the function of the 
> double façade or the energy consumption of the air system to maintain 
> the functionality of the double façade. Beyond the improvement of the 
> U value we can then start looking at improved shading coefficients and 
> surface temperature control of the inside surface of the double 
> façade. For these different aspects of double façade design I believe 
> the design criteria was simplified in a series of tables issued in a 
> couple of ISSO publications in the 80's. These documents will get you 
> rough data to be able to assess whether or not the double façade is 
> feasible. As far as deluxe simulation tools probably the best is the 
> ROOM program by Mike Holmes and Andrew White and then there is also 
> TRNSYS.
>
> Getting back to Nick's comments, I have found over the years that the 
> most comments regarding double facades come from people that have 
> never designed them, here I am referring to the article and not you Nick.
>
> I first started designing double facades in the late 70's in the 
> Netherlands and over the years have designed quite few and completed 
> quite a few repair jobs on attempted double facades. One thing I have 
> learned is that if it isn't cold then the double façade is there for 
> show only!
>
>  
>
> *Peter Simmonds, Ph.D. *
> *Senior Associate
> Head of the Advanced Technology Group
> **IBE Consulting Engineers*
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> *From:* Nick Caton [mailto:ncaton at smithboucher.com]
> *Sent:* Thursday, November 11, 2010 8:11 AM
> *To:* Sami, Vikram; bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Is there a quick model for double skins 
> facades?
>
>  
>
> Hi Vik,
>
>  
>
> I hate to trample over anyone's little flower patch, but I've read 
> some scathing assessments of double-facades as an energy-saving 
> strategy.  You might want to check this and the associated references 
> out: 
> http://www.buildingscience.com/documents/insights/bsi-007-prioritizing-green-it-s-the-energy-stupid. 
>
>
>  
>
> That said you might not be satisfied until you develop your own 
> conclusions.  Proponents of this approach repeatedly cite benefits of 
> CFD, so to give a "fair/proper" assessment any tool you work with 
> would probably need to be modeling convective airflows between floors.
>
>  
>
> ~Nick
>
>  
>
> cid:489575314 at 22072009-0ABB* *
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>
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>  
>
> *From:* bldg-sim-bounces at lists.onebuilding.org 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Sami, 
> Vikram
> *Sent:* Thursday, November 11, 2010 8:59 AM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Is there a quick model for double skins facades?
>
>  
>
> We are doing a project in a pretty cold climate. The project design 
> has a really big glass façade facing south. One of the ideas to reduce 
> conductive heat loss is to create a double skin façade on the south side.
>
>  
>
> Now I realize that this is going to take a fair amount of analysis 
> work to design it properly. What I was wondering is if there is a 
> quick analysis tool/methodology to tell if this is even feasible to go 
> into more detailed analysis.
>
>  
>
> Any help would be much appreciated
>
>  
>
> *Vikram Sami*, LEED AP
>
> Sustainable Design Analyst
>
> 1382 Peachtree St. NE, Atlanta, GA 30309
>
> t: 404-443-7462    f: 404.892.5823       e: 
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> <http://www.perkinswill.com/>
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