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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I’m starting a new “thread” as this is a
definite tangent from the emissivity discussion of the past few days.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>A question occurred to me on reading Ralph / Chris’s
comments below… does <u>ANY</u> energy modeling program/engine today use
the snow cover data present in TMY2 files? There’s obvious
implications for things like roof surface thermal behavior and hourly photovoltaic
array performance when you consider the reality of significant snow cover
presence through the day…<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Of note… I’m no expert, but for others’
reference I found a nice resource this afternoon clarifying the what/why/how of
TMY files here: <a href="http://rredc.nrel.gov/solar/pubs/tmy2/">http://rredc.nrel.gov/solar/pubs/tmy2/</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>~Nick<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><img border=0 width=119 height=37 id="Picture_x0020_1"
src="cid:image001.jpg@01CA736D.238D1B00" alt="cid:489575314@22072009-0ABB"></span><b><span
style='font-size:11.0pt;font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p></o:p></span></b></p>
<p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Stylus BT","sans-serif";
color:#2D4D5E'><o:p> </o:p></span></b></p>
<p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Stylus BT","sans-serif";
color:#2D4D5E'>NICK CATON, E.I.T.</span></b><b><span style='font-family:"Stylus BT","sans-serif";
color:#2D4D5E'><o:p></o:p></span></b></p>
<p class=MsoNormal><span style='font-size:7.5pt;font-family:"Calibri","sans-serif";
color:#CC9900'>PROJECT ENGINEER</span><span style='font-size:7.5pt;color:#CC9900'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Calibri","sans-serif";
color:#2D4D5E'>25501 west valley parkway<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Calibri","sans-serif";
color:#2D4D5E'>olathe ks 66061<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Calibri","sans-serif";
color:#2D4D5E'>direct 913 344.0036<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Calibri","sans-serif";
color:#2D4D5E'>fax 913 345.0617<o:p></o:p></span></p>
<p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Calibri","sans-serif";
color:#2D4D5E'>Check out our new web-site @ </span></i><span style='font-size:
11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><a
href="www.smithboucher.com" title="blocked::www.smithboucher.com"><span
style='font-size:10.0pt'>www.smithboucher.com</span></a></span><u><span
style='font-size:10.0pt;font-family:"Calibri","sans-serif";color:blue'> </span></u><span
style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <b>On Behalf Of </b>Ralph
Muehleisen<br>
<b>Sent:</b> Wednesday, December 02, 2009 10:48 AM<br>
<b>To:</b> Christopher Schaffner<br>
<b>Cc:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> Re: [Bldg-sim] Why should roofs have high emissivity?<o:p></o:p></span></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'>True indeed.<br>
<br>
Except when your roofs are not covered with snow.<br>
<br>
Here in Chicago, at least the past few years, snow has come in bigger
chunks with more warmi and cold periods in between. And rooftop snow has
been melting during the warm periods so rooftops have been bare for more
of the winter.<br>
<br>
It would be an interesting study (maybe I can find an undergrad or interested
masters student) to actually look at a typical flat roof small commercial
building and see if the increased summer efficiency of cooling equipment from a
cool roof offsets the increased winter heating load.<br>
<br>
Ralph<br>
<br clear=all>
Ralph Muehleisen, Ph.D., P.E., LEED AP, FASA<br>
Assistant Professor and Director of the Miller Acoustics Lab<br>
Civil, Architectural and Environmental Engineering<br>
Illinois Institute of Technology<br>
Chicago, IL 60616<br>
<a href="mailto:muehleisen@iit.edu">muehleisen@iit.edu</a><br>
tel: 312-567-3545 fax:312-567-3519<br>
<br>
<o:p></o:p></p>
<div>
<p class=MsoNormal>On Wed, Dec 2, 2009 at 5:47 AM, Christopher Schaffner <<a
href="mailto:chris@greenengineer.com">chris@greenengineer.com</a>> wrote:<o:p></o:p></p>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Verdana","sans-serif"'>Of
course, if your roof is well insulated, it will be covered with snow. I doubt
very much that your “warm” roof will really help much. Go with the
cool roof. <br>
<br>
--<br>
<br>
Chris Schaffner, PE, LEED AP, LEED Faculty™<br>
Founder and Principal<br>
<br>
The Green Engineer, LLP<br>
Sustainable Design Consulting<br>
50 Beharrell Street<br>
Concord, MA 01742<br>
T: 978.369.8978<br>
M:978.844.1464<br>
<a href="http://chris@greenengineer.com" target="_blank">chris@greenengineer.com</a><br>
<a href="http://www.greenengineer.com" target="_blank">www.greenengineer.com</a><o:p></o:p></span></p>
<div>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;
font-family:"Verdana","sans-serif"'><br>
<br>
<br>
On 12/2/09 12:26 AM, "Ralph Muehleisen" <<a
href="http://muehleisen@gmail.com" target="_blank">muehleisen@gmail.com</a>>
wrote:<o:p></o:p></span></p>
</div>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'>
<div>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Verdana","sans-serif"'>Chris
makes a good point to consider with cool roofs.<br>
<br>
A cool roof will indeed reduce solar heat gain to the roof which reduces its
temp (good in summer) and reduces cooling requirements in summer but will
increase heating requirements in the winter.<br>
<br>
Until someone develops a material where the emissivity changes with temperature
(and not just wavelength) a cool roof that is good in summer will be bad in
winter.<br>
<br>
So, in colder climates, a cool roof can indeed increase the overall energy use
of a building.<br>
<br>
Even so, some northern cities like Chicago, mandate cool roofs in building
code. Why? Because the cool roof will reduce the urban heat island
effect where the city has increased temperatures compared to the surrounding
areas. <br>
<br>
The thought is that the overall benefits of the reduction in urban heat
island effect in summer is more important than the increased energy use that
comes from increased winter cooling load.<br>
<br>
<br>
Ralph<br>
<br>
Ralph Muehleisen, Ph.D., P.E., LEED AP, FASA<br>
Assistant Professor and Director of the Miller Acoustics Lab<br>
Civil, Architectural and Environmental Engineering<br>
Illinois Institute of Technology<br>
Chicago, IL 60616<br>
<a href="http://muehleisen@iit.edu" target="_blank">muehleisen@iit.edu</a><br>
tel: 312-567-3545 fax:312-567-3519<br>
<br>
<br>
On Tue, Dec 1, 2009 at 6:28 PM, Chris Jones <<a href="http://cj@cr-jay.ca"
target="_blank">cj@cr-jay.ca</a>> wrote:</span><o:p></o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:11.0pt;
font-family:"Verdana","sans-serif"'>In some cases it may be counter productive
to use a high emissivity roof. I have worked on uncooled warehouses where
the team used an approved roofing product to get that point but the heating
energy increased enough to lower the savings enough to lose an EAc1
point. <br>
<br>
<br>
<br>
<br>
<br>
<br>
Chris Jones<br>
14 Oneida Avenue<br>
Toronto, ON M5J 2E3.<br>
Tel. 416-203-7465<br>
Fax. 416-946-1005<br>
<br>
<br>
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