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<DIV dir=ltr align=left><SPAN class=468535515-03122009><FONT color=#0000ff
size=2 face=Arial>Yes, EnergyPlus uses the albedo in the TMY3 or snow cover in
other files to adjust the diffuse radiation.</FONT></SPAN></DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <B>On Behalf Of </B>Nick
Caton<BR><B>Sent:</B> Wednesday, December 02, 2009 5:48 PM<BR><B>To:</B>
muehleisen@iit.edu; Christopher Schaffner<BR><B>Cc:</B>
bldg-sim@lists.onebuilding.org<BR><B>Subject:</B> [Bldg-sim] Rooftop Snow
Cover???<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">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-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">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-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">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-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">~Nick<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><IMG
id=Picture_x0020_1 border=0 alt=cid:489575314@22072009-0ABB
src="cid:468535515@03122009-2223" width=119 height=37></SPAN><B><SPAN
style="FONT-FAMILY: 'Stylus BT','sans-serif'; COLOR: #2d4d5e; FONT-SIZE: 11pt"><o:p></o:p></SPAN></B></P>
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style="FONT-FAMILY: 'Stylus BT','sans-serif'; COLOR: #2d4d5e; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></B></P>
<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 'Stylus BT','sans-serif'; COLOR: #2d4d5e; FONT-SIZE: 11pt">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
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ks 66061<o:p></o:p></SPAN></P>
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913 345.0617<o:p></o:p></SPAN></P>
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style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #2d4d5e; FONT-SIZE: 10pt">Check
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<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; FONT-SIZE: 10pt">From:</SPAN></B><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; FONT-SIZE: 10pt">
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 style="MARGIN-BOTTOM: 12pt" class=MsoNormal>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-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 11pt">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 style="MARGIN-BOTTOM: 12pt" class=MsoNormal><SPAN
style="FONT-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 11pt"><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: 5pt; MARGIN-BOTTOM: 5pt">
<DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 11pt">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 style="MARGIN-BOTTOM: 12pt" class=MsoNormal><SPAN
style="FONT-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 11pt">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>_______________________________________________<BR>Bldg-sim
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<P style="MARGIN-BOTTOM: 12pt" class=MsoNormal><SPAN
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