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

Peter Simmonds peter.simmonds at ibece.net
Thu Nov 11 08:58:54 PST 2010


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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Sherman Oaks, CA 91423 
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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

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olathe ks 66061

direct 913 344.0036

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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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