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<DIV><FONT size=2 face=Arial>Yes, it makes sense. High emissivity allows a
roof to radiate its stored heat to the sky, thus aiding the cooling effect, so,
yes, good for hot climates!</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Note also that ASHRAE 90.1 gives credit for (i.e.,
relaxes) the U-Factor requirement for such roofs in climate zones 1, 2 and 3
(the warmest zones). The ASHRAE Standard uses the term "High
Albedo" for roofs with high reflectance AND high emissivity -- this is
addressed in Section 5.5.3.1.1 and Table 5.5.3.1 in the 2007
version.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2 face=Arial>Regards,</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2 face=Arial>===========================<BR>Larry O. Degelman,
P.E.<BR>Professor Emeritus of Architecture<BR>Texas A&M
University<BR>College Station, TX 77845<BR><A
title="mailto:ldegelman@suddenlink.net CTRL + Click to follow link"
href="mailto:ldegelman@suddenlink.net">ldegelman@suddenlink.net</A><BR>===========================</FONT></DIV>
<DIV style="FONT: 10pt Tahoma">
<DIV><BR></DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A title=bradpainting@gmail.com
href="mailto:bradpainting@gmail.com">Brad Painting</A> </DIV>
<DIV><B>Sent:</B> Sunday, November 29, 2009 2:57 PM</DIV>
<DIV><B>To:</B> <A title=bldg-sim@lists.onebuilding.org
href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</A>
</DIV>
<DIV><B>Subject:</B> [Bldg-sim] Why should roofs have high
emissivity?</DIV></DIV></DIV>
<DIV><BR></DIV>It seems to me that a roof that emits more radiation will have a
greater warming effect on the building. Some houses in warm climates have
radiant barriers because the aluminum has a <I>low</I> emissivity, thus blocking
the infrared radiation. But both LEED and Energy Star suggest high emissivity
for warm climates. Does this make sense?<BR><BR>From LEED NC Reference Guide v.
2.2:<BR><BR>"To maximize energy savings and minimize heat island effects,
materials must exhibit a high reflectivity and a high emissivity over the life
of the product."<BR><BR>>From Energy Star website:<BR><BR>"In warm and sunny
climates highly emissive roof products can help reduce the cooling load on the
building by releasing the remaining heat absorbed from the
sun."<BR><BR>Thanks,<BR><BR>Brad<BR>
<P>
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