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

[Nick Caton]

Peter, Marques et al:

 

Thank you so much for sharing your collective insights!  My initial comments were intended only to open the discussion, as I have heard contrarian opinions in the past and didn't want a friend to be unaware of them =).  Consider me an interested student, certainly not an authority on the subject!

 

I for one have been motivated by this discussion to do some homework, and now have a much better grasp of the fundamentals.  Apparently ASHRAE Journal put out a good primer roughly a year ago for others in the same boat of curiosity to understand the concepts and challenges present in DSF design better - I found this handy:  http://www.rwdi.com/cms/publications/76/200904_Ventilating_Facades.pdf

 

Thanks again,

 

~Nick

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: Marques da Silva [mailto:fms at lnec.pt] 
Sent: Friday, November 12, 2010 3:32 AM
To: Peter Simmonds
Cc: Nick Caton; Sami, Vikram; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Is there a quick model for double skins facades?

 

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
14130 Riverside Drive, Suite 201
Sherman Oaks, CA 91423 
p: (818) 377-8220 x246 m: (818) 219-1284 f: (818) 377-8230

www.ibece.com <http://www.ibece.com/> 
Ideas for the built environment 

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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 

  



  

NICK CATON, E.I.T. 

PROJECT ENGINEER 

25501 west valley parkway 

olathe ks 66061 

direct 913 344.0036 

fax 913 345.0617 

Check out our new web-site @ www.smithboucher.com 

  

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: vikram.sami at perkinswill.com   www.perkinswill.com <http://www.perkinswill.com/>  

Perkins+Will.  Ideas + buildings that honor the broader goals of society 

 Years of Design Innovation 

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