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<font face="Helvetica, Arial, sans-serif">Hiya George. Of course I
know it is per unit length, as I quoted the units of W/mK<br>
So if I have a 5' by 4' window (1.5 x 1.2m) the additional heat
loss of 0.01 W/mK is 0.054 W/mK or in 0 F weather, 2 Watts. Lets
say we allow us 0.03 W/mK difference between the ideal location
and the location preferred by the owner, or builder, or the window
durability. Now we are up to 6 Watts/window. In a house with 12
windows, this is 72 Watts, at DESIGN CONDITIONS for Zone 5, and we
have 2000 W flowing through the windows themselves. The prescence
of absence of overhangs and neighboring buildings will likely have
this much impact on heat loss. <br>
The real reason to worry about this stuff are the examples of when
it is done horribly, and you have a 0.2 W/mK (which works out to
41W/window or 500W for 12 windows at design) detail and you start
to risk condensation on the window edge.<br>
<br>
But none of this provides technical support to the comment "the
window has to be near the middle", as opposed to "the window has
to be within the primary insulation layers".<br>
<br>
There are north american windows which have the same drip edge as
Euro windows, and which use the same type of clips to attach the
frame to the structure, they just tend to be more commercial or
weird Canadian types. Flanged windows are a very North American
thing which are pretty recent (20 years). I bet they will become
less important as people start to ask about how they should locate
their windows.<br>
<br>
PS. George, and many of the experienced designers, know about the
importance of things like draining the rough opening, but you
would never know it from the PHPP and the drawings out there.<br>
</font>
<pre class="moz-signature" cols="0">Dr John Straube, P.Eng.
<a class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></pre>
<br>
On 12-01-29 11:55 PM, George J. Nesbitt wrote:
<blockquote cite="mid:4F2622CB.30301@houseisasystem.com" type="cite">
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John,<br>
the thermal bridge values are per unit length of window, so it
adds up, and can be a large % of the total annual demand. The
sills usually have higher values than the sides & top which
are easier to insulate over.<br>
<br>
Yes, German (European, Passive House, etc.) windows need rough
opening space too, and it should be insulated, preferably with
foam. They differ in having a sill that attaches to the frame with
a drip on the cladding. The windows are also flashed on the sides
and tops, not clear from the drawings.<br>
<br>
I agree that sacrificing some energy efficiency for durability
is a good idea if needed. Windows & doors should have sloped
sills with pan flashing, and allowed to drain out. <br>
<br>
I just got word that I passed my Certified Passive House
Consultant test (for the 2nd time, fallout from PHIUS)<br>
<br>
<br>
<br>
On 1/29/2012 5:55 PM, John Straube wrote:
<blockquote cite="mid:4F25F88D.10605@gmail.com" type="cite">
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<font face="Helvetica, Arial, sans-serif">Bonjour mon ami<br>
<br>
I have the PHPP 2007. It shows some drawings on Page 71, but
does not show the impact of moving the window inward or
outward. It does show a wood frame wall and the fact that this
has one of the lowest thermal flanking loss (0.01 W/mK) as
shown of the four examples. It also shows a window
installation that would result in serious rot and damage when
the window leaks (windows have a high likelihood of leaking),
but I suppose that is not an energy issue ;)<br>
<br>
The Chisnall pdf shows a great example of the impact of being
really stupid, that is, putting the window in the masonry part
of the wall, and have all the insulation outboard of that.
OK, this is a big mistake, and has nothing to do with being in
the center of the wall or the center of the insulation. It is
a major problem caused by the window being installed in the
uninsulated part of the wall. Ironically, this powerpoint also
seems to show this error being committed in the photo on page
16.<br>
<br>
That one image from the passive house pdf is the close to the
answering the question, although the detail is extreme: the
window is again pushed as far out as possible, has a lot of
solid wood around it and does not actual have insulation
around it (like most windows are installed here).<br>
<br>
The passidia shows that the difference between mounting in
middle and flush to exterior is merely 0.001 W/m K. That is
very very small. Only when you install the window in the
masonry (completely missing the insulation layer) does the
thermal bridge value increase to 0.204 (obviously stupid).<br>
<br>
So again, I dont see any definitive answer that the window
needs to be installed in the middle of the wall or the middle
of the insulation (however that is defined anyway). I also
have no definitive answer (which is why I asked) but in the
range of reasonable installations, the impact seems seems to
be small or even non-existent (by small I mean <0.03 or so
W/mK). Of course, the window needs to be installed with the
insulation layer, and it should ideally be surrounded by some
insulation in the rough opening. Many of the PH drawings are
unbuildable, as they show no rough opening (I have worked in
Europe and I know that the window rough openings are sized
larger than the window to allow for installation, just like
they are in north America).<br>
<br>
</font>
<pre class="moz-signature" cols="0">Dr John Straube, P.Eng.
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></pre>
<br>
On 12-01-29 12:19 PM, John Daglish wrote:
<blockquote cite="mid:92732805.20120129181909@free.fr"
type="cite">
<pre wrap="">Bonjour John,
Sorry not to get back sooner, have been busy.
They calculate the installed value of the thermal bridge heat loss
coefficient W/m.K.
If you look at page 71 of the PPHPP assive House Planning Package 2007 booklet it
shows some best practices for exterieur insulation, concrete form
block, timber I beam, timber frame.
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://www.can.uk.net/conference_2011/leicester/downloads/peter_chisnall.pdf">http://www.can.uk.net/conference_2011/leicester/downloads/peter_chisnall.pdf</a>
p27 cavity wall insulation 0.11 0.01 or 0.12 W/m.K ext mid int
p28-29 external wall insulation 0.08 or 1.84 W/m.K "mid" int
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://gse.cat.org.uk/downloads/passive_house.pdf">http://gse.cat.org.uk/downloads/passive_house.pdf</a>
p9-10
There is a more complete explanation on the web site <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://passipedia.passiv.de/passipedia_en/start">http://passipedia.passiv.de/passipedia_en/start</a>
but it is behind a "pay" wall ie. you have to become a member.
but not in German it seems :
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://passipedia.passiv.de/passipedia_de/planung/waermeschutz/fenster/fenstereinbau">http://passipedia.passiv.de/passipedia_de/planung/waermeschutz/fenster/fenstereinbau</a>
external wall insulation ETICS
0.18 or 0.017 or 1.22 W/m.K ext mid int
0.86 or 0.84 or 1.22 W/m2.K window installed U value
PS angle bracket fixings to place the window in an ETICS wall should
have thermal insulating shims!! Even the cavity wall brick fixings
fabricants are doing this now.
Cordialement
</pre>
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<br>
<br>
<div class="moz-signature">-- <br>
George J. Nesbitt, Environmental Design / Build, Building
Performance Contractor HERS I Verifier & HERS II Rater,
GreenPoint Rater new & existing SF & MF, CABEC CEPE
(Certified Energy Plans Examiner), Certified Passive House
Consultant, BPI Multifamily Analyst, <a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="http://www.houseisasystem.com">www.houseisasystem.com</a>,
(510) 655-8532 office, (510) 599-5708 mobile</div>
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