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Hi Peter <br>
<br>
I think you are only considering DSF gap forced ventilation (<span><i>when
the air system was switched off after occupation?</i>). 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.<br>
I don't know ROOM but TRNSYS is a good option for modelling DSF (see
the work of Haase et al).<br>
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...<br>
</span>
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<p><span>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. </span></p>
<p><span>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. </span></p>
<p><span>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! </span></p>
<p><span> </span></p>
<div>
<div>
<p><b><span>Peter Simmonds, Ph.D. </span></b><span><br>
</span><b><span>Senior Associate<br>
Head of the Advanced Technology Group<br>
</span></b><b><span>IBE Consulting
Engineers</span></b><span><br>
</span><b><span>14130 Riverside Drive,
Suite 201</span></b><span><br>
</span><b><span>Sherman Oaks, CA 91423 <br>
p: (818) 377-8220 </span></b><b><span>x246</span></b><b><span> m:
(818) 219-1284 f: (818) 377-8230<br>
<br>
</span></b><b><span><a moz-do-not-send="true"
href="http://www.ibece.com/" title="http://www.ibece.com/"><span>www.ibece.com</span></a><br>
</span></b><b><i><span>Ideas for the built
environment</span></i></b><span> </span></p>
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<div>
<p><b><span>From:</span></b><span> Nick Caton
[<a class="moz-txt-link-freetext" href="mailto:ncaton@smithboucher.com">mailto:ncaton@smithboucher.com</a>] <br>
<b>Sent:</b> Thursday, November 11, 2010 8:11 AM<br>
<b>To:</b> Sami, Vikram; <a class="moz-txt-link-abbreviated" href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] Is there a quick model for double
skins facades? </span></p>
</div>
</div>
<p> </p>
<p><span>Hi Vik, </span></p>
<p><span> </span></p>
<p><span>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: <a
moz-do-not-send="true"
href="http://www.buildingscience.com/documents/insights/bsi-007-prioritizing-green-it-s-the-energy-stupid">http://www.buildingscience.com/documents/insights/bsi-007-prioritizing-green-it-s-the-energy-stupid</a>.
</span></p>
<p><span> </span></p>
<p><span>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. </span></p>
<p><span> </span></p>
<p><span>~Nick </span></p>
<p><span> </span></p>
<div>
<p><span><img src="cid:part1.07080009.07000504@lnec.pt"
alt="cid:489575314@22072009-0ABB"></span><b><span> </span></b></p>
<p><b><span> </span></b></p>
<p><b><span>NICK CATON, E.I.T.</span></b><b><span> </span></b></p>
<p><span>PROJECT ENGINEER</span><span> </span></p>
<p><span>25501 west
valley parkway </span></p>
<p><span>olathe ks 66061 </span></p>
<p><span>direct 913
344.0036 </span></p>
<p><span>fax 913
345.0617 </span></p>
<p><i><span>Check out
our new web-site @ </span></i><span><a moz-do-not-send="true"
href="www.smithboucher.com" title="blocked::www.smithboucher.com"><span>www.smithboucher.com</span></a></span>
<span> </span> <span> </span></p>
</div>
<p><span> </span></p>
<div>
<div>
<p><b><span>From:</span></b><span>
<a class="moz-txt-link-abbreviated" href="mailto:bldg-sim-bounces@lists.onebuilding.org">bldg-sim-bounces@lists.onebuilding.org</a>
[<a class="moz-txt-link-freetext" href="mailto:bldg-sim-bounces@lists.onebuilding.org">mailto:bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of </b>Sami,
Vikram<br>
<b>Sent:</b> Thursday, November 11, 2010 8:59 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> [Bldg-sim] Is there a quick model for double skins
facades? </span></p>
</div>
</div>
<p> </p>
<p>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. </p>
<p> </p>
<p>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. </p>
<p> </p>
<p>Any help would be much appreciated </p>
<p> </p>
<p><b><span>Vikram Sami</span></b><span>, LEED AP </span></p>
<p><span>Sustainable Design Analyst </span></p>
<p><span>1382 Peachtree St. NE, Atlanta, GA
30309 </span></p>
<p><span>t: 404-443-7462
f: </span><span lang="ES">404.892.5823 </span><span> e:
<a class="moz-txt-link-abbreviated" href="mailto:vikram.sami@perkinswill.com">vikram.sami@perkinswill.com</a> </span><a moz-do-not-send="true"
href="http://www.perkinswill.com/"><span>www.perkinswill.com</span></a><span>
</span></p>
<p><b><span>Perkins+Will.</span></b><span> </span><span>Ideas +
buildings that honor the broader goals of society</span><span> </span></p>
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alt="75logo_only.gif"></span></b><span>Years of Design Innovation</span><b><span>
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