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<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2>Nick,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009> <FONT
face=Arial color=#0000ff size=2>I am curious - and you might need to consider -
whether <EM>absorbtance</EM> is really the same thing as <EM>absorbtivity</EM>
(and check my spelling using <EM>b</EM> instead of <EM>p</EM> - not sure there,
either). Similarly, are <EM>emission</EM> and<EM> emissivity</EM> truly
synonymous? I'm pretty sure that Mr. K's law refers to behavior in a
situation, whereas eQuest is asking for material properties.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009> <FONT
face=Arial color=#0000ff size=2>Is anyone else clearer on this than I
am?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2>Lars Fetzek, EI</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2>Phoenix Engineering Group</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=791232314-29092009><FONT face=Arial
color=#0000ff size=2>Tampa, Florida</FONT></SPAN></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> equest-users-bounces@lists.onebuilding.org
[mailto:equest-users-bounces@lists.onebuilding.org] <B>On Behalf Of </B>Nick
Caton<BR><B>Sent:</B> Monday, September 28, 2009 6:49 PM<BR><B>To:</B> Ed
Garcia<BR><B>Cc:</B> equest-users@lists.onebuilding.org<BR><B>Subject:</B> Re:
[Equest-users] Cool Roofs<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Hi Ed,<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">I would account for emissivity
by specifying the absorptance property of the surface in the detailed edit mode
(spreadsheet view is fastest way to edit multiple roof constructions). For
the purposes of defining roof constructions to figure out their thermal
behavior*, Emissivity = Absorptance. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">The solar reflective index (SRI)
is another way of defining the same thing, based on a different scale between
some grade of white and black paint rather than absolutes (zero-to-1.0).
There are probably charts out there that could translate SRI into
absorptance/emissivity if you have only the SRI to go off
of…<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Right-click in eQuest one of the
cells for entering your construction absorptance, and you’ll be led to a DOE
help file that has a handy reference chart of absorptances of various exterior
finishes.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">-----<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">* Since I know we’re
a group of learners, I figured you and others might be interested to hear
(correct?) my logic behind “emissivity = absorptance” for modeling roof
constructions in eQuest and other energy modeling ventures...
<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">First, let me relate my
understanding of emissivity through glass: Light energy hitting glass does
one of three things – (A) reflect off the surface, (B) transmit through the
glass, (C) absorb into the glass as heat energy. Absorbed light energy
(option C) is simultaneously radiated (aka “emitted” ala “emissivity) from both
sides of the glass (into and outside of your building). “Low-e” glass is
glass that has a low emissivity, and thus doesn’t get really hot and heat up
your building via heat radiation as much in the summer when hit by
daylight.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Where emissivity is a
<U>fraction of radiation emitted</U> from a surface, absorptance is a measure of
the </SPAN><U>fraction of radiation absorbed</U>. One is energy out, the
other is energy in.<SPAN style="COLOR: #1f497d"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">To ground my explanation a bit,
I googled up something from my thermodynamics courses that had gone a bit
fuzzy: <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><A
href="http://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation">Kirchoff’s
law</A>: “</SPAN>At thermal equilibrium, the <A title=Emissivity
href="http://en.wikipedia.org/wiki/Emissivity">emissivity</A> of a body (or
surface) equals its <A title=Absorptivity
href="http://en.wikipedia.org/wiki/Absorptivity">absorptivity</A>.”<SPAN
style="COLOR: #1f497d"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">If we assume, for the purposes
of thermal energy modeling, that within each modeled hour the roof construction
is in thermal equilibrium (not in the process of heating up or cooling down), we
can say “radiation in = radiation out,” and apply Mr. K’s law above, concluding
Emissivity = Absorptance. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">The potential inaccuracy of this
assumption lies in the reality of how a “cold” roof, for example, in the morning
hours will absorb more heat into its construction than it emits, until it
reaches a thermal equilibrium point later in the day. In the evening
hours, the reverse will be true and the roof will radiate heat at a higher
fraction than its absorptivity. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">That said, I am
<B><I>semi-confident</I></B> that eQuest and other programs using a
“construction by layers” methodology will compensate for such an inaccuracy by
approximating the actual absorption/radiation effects of thermal massing over
time. If I’m wrong on that point, I will have to lick my wounds and hope
someone on this list can set me straight before I drive this eQuest train into a
wall! <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">In other words, I’d love to be
corrected if it’s in order =). Otherwise, hope this
helps!<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">~Nick<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
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height=37 alt=cid:489575314@22072009-0ABB src="cid:791232314@29092009-0740"
width=119 border=0></SPAN><B><SPAN
style="COLOR: #2d4d5e; FONT-FAMILY: 'Stylus BT','sans-serif'"><o:p></o:p></SPAN></B></P>
<P class=MsoNormal><B><SPAN
style="COLOR: #2d4d5e; FONT-FAMILY: 'Stylus BT','sans-serif'"><o:p> </o:p></SPAN></B></P>
<P class=MsoNormal><B><SPAN
style="COLOR: #2d4d5e; FONT-FAMILY: 'Stylus BT','sans-serif'">NICK CATON,
E.I.T.</SPAN></B><B><SPAN
style="FONT-SIZE: 12pt; COLOR: #2d4d5e; FONT-FAMILY: 'Stylus BT','sans-serif'"><o:p></o:p></SPAN></B></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 7.5pt; COLOR: #cc9900">PROJECT
ENGINEER</SPAN><SPAN
style="FONT-SIZE: 7.5pt; COLOR: #cc9900; FONT-FAMILY: 'Times New Roman','serif'"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: #2d4d5e">25501 west
valley parkway<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: #2d4d5e">olathe ks
66061<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: #2d4d5e">direct 913
344.0036<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: #2d4d5e">fax 913
345.0617<o:p></o:p></SPAN></P>
<P class=MsoNormal><I><SPAN style="FONT-SIZE: 10pt; COLOR: #2d4d5e">Check out
our new web-site @ </SPAN></I><SPAN style="COLOR: #1f497d"><A
title=blocked::www.smithboucher.com href="www.smithboucher.com"><SPAN
style="FONT-SIZE: 10pt">www.smithboucher.com</SPAN></A></SPAN><U><SPAN
style="FONT-SIZE: 10pt; COLOR: blue"> </SPAN></U><SPAN
style="COLOR: #1f497d"><o:p></o:p></SPAN></P></DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<DIV>
<DIV
style="BORDER-RIGHT: medium none; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; PADDING-LEFT: 0in; PADDING-BOTTOM: 0in; BORDER-LEFT: medium none; PADDING-TOP: 3pt; BORDER-BOTTOM: medium none">
<P class=MsoNormal><B><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">From:</SPAN></B><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">
equest-users-bounces@lists.onebuilding.org
[mailto:equest-users-bounces@lists.onebuilding.org] <B>On Behalf Of </B>Ed
Garcia<BR><B>Sent:</B> Monday, September 21, 2009 9:44 AM<BR><B>To:</B>
<B>Subject:</B> [Equest-users] Cool Roofs<o:p></o:p></SPAN></P></DIV></DIV>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>I a new user to eQuest and need to model cool roofs. I
see the user specified roof properties, but I do not see how to add the SRI or
emissivity of the roof. Would appreciate some guidance.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'">Regards,<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'">Ed<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'"><o:p> </o:p></SPAN></P></DIV></BODY></HTML>