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One thing I have come across is the thickness of the trapped air
layer in thermal panes. Up to about 5/8", industry standard is
1/2", the laminar layers on both pieces of glass restrict the
convection current in the air space. Once you get to 3/4" of
spacing the R-value of the trapped air goes way down. Most of the
insulating value of a couple pieces of glass that is very poor to
begin with. Low E coatings work best when there is sunshine which
in the summer can be half the day. In the winter that might only be
1/3 of a day. The rest of the time you are radiating energy out
through the glass. So a standard thermal pane is about R-2, add low
E coatings, argon or krypton gas, warm edge spacers etc and you can
get to R-4 for 2 pieces of glass. Tuning your low E coatings
depends on where you are. There is a big difference between a
Canadian low E vs a Florida low E when it comes to effectiveness in
the specific climate. But in the end you are only playing with R-2
and only if you keep the air space thin. Then there is the laminar
layer on the outside of the glass, can be R-1.3, I think, if you
minimize that convection current, ie have the outer layer of glass
inset so the wind can't sweep it as easily. Windows are tricky. I
can easily build an R-28 wall for a fraction of the cost of a window
and almost no air leakage. But it is nice to see the sun.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
<br>
<div class="moz-cite-prefix">On 9/7/2017 6:02 PM, Nicholas Caton via
Equest-users wrote:<br>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">The
“assembly 0.67” for a single layer of glass leaves me a
little uncertain – I think if you dig deeper you might find
the manufacturer may have some helpful context around that
figure. Do they suggest the net impact of the low-e glass,
associated framing, trapped air layer, and conductive
transfer of the seals in contact with the existing assembly
nets an effective U-0.67 for a given/standard window size?
If so, your math looks pretty okay for the assumptions
stated (just expand on what that 0.67 means in documenting
your approach)! If not or if this isn’t made very clear,
you may need to perform a more involved analysis to account
for one or more of those items.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">For
savings accuracy with existing/historical window retrofits
(not always a priority with LEED certification,
understandably), I might also be interested (resources
permitting) to test a mockup installation before & after
to explore the impact on infiltration reduction in your
model. That may more fully capture the cost:benefit ratio
if the value of the measure is under active consideration.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">~Nick<o:p></o:p></span></p>
<p class="MsoNormal"><span
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src="cid:part1.E0F2BE85.73658A31@bellnet.ca" class=""
height="9" width="726"><o:p></o:p></span></p>
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Arial",sans-serif;color:#3A7A46">Nick
Caton, P.E., BEMP</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#3A7A46"><o:p></o:p></span></p>
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Senior Energy Engineer</span><span
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</span><span
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Regional Energy Engineering Manager<o:p></o:p></span></p>
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Energy and Sustainability Services</span><span
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Schneider Electric</span><span
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style="font-size:8.0pt;font-family:"Arial",sans-serif;color:#626469">913.564.6361
</span><span
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Santa Fe Trail Drive<br>
Suite 204<br>
Lenexa, KS 66219<br>
United States</span><span
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<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">
Equest-users
[<a class="moz-txt-link-freetext" href="mailto:equest-users-bounces@lists.onebuilding.org">mailto:equest-users-bounces@lists.onebuilding.org</a>]
<b>On Behalf Of </b>Morteza Kasmai via Equest-users<br>
<b>Sent:</b> Thursday, September 07, 2017 4:44 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
<b>Subject:</b> [Equest-users] Modifying existing historic
windows<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;margin-bottom:12.0pt"><br>
<span
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#274E13">Dear
all,</span><br>
<br>
<span
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#274E13">I
am modeling a historic building and the scope of work is
to modify the existing windows by adding a storm window
to the existing industrial steel sash windows. The storm
window is one layer Low-E glass with aluminum framing
with brake (assembly U-0.67).</span><br>
<span
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#274E13">Assuming
the existing one layer clear glass window has U-value of
5.8, can I assume the assembly R-value of the window
system as the total R-values of both of the windows as
following, and would it be acceptable by the LEED
reviewer?</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;margin-bottom:12.0pt;background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial"><span
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#274E13">Total
R-Value: 1/5.8 + 1/0.67 = 0.172 + 1.49 = 1.662<br>
U-Value = 1/1.662 = 0.6</span><span
style="font-family:"Tahoma",sans-serif;color:#274E13"><o:p></o:p></span></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial"><span
style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#274E13">I
would appreciate your help in this matter,<br>
Morteza</span><span
style="font-family:"Tahoma",sans-serif;color:#274E13"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
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</div>
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<p class="MsoNormal"><o:p> </o:p></p>
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