The point related to decrease in reflectivity due to dust deposition (as indicated by Charlie) is quite significant (especially in dusty areas, places with high SPM in air, and having less rain) which may become one of the major causes for deviation of the actual energy saving from simulation results. One may have to exert little more while attempting to calibrate the model with actual results if the dust is not cleaned periodically. <br>
<br>jyotirmay mathur<br><br>Dr.-Ing. Jyotirmay Mathur<br>Coordinator, Energy Engineering Program<br>Associate Professor, Mechanical Engineering Department<br>Malaviya National Institute of Technology<br>J.L.N. Marg, Jaipur (India) -302 017<br>
Phone: <br>+91-141-2529109 (R)<br>+91-141-2529061 (o), 2713211 (direct)<br>+91-94142-50329 (mobile)<br><a href="http://jyotirmaymathur.tripod.com/">http://jyotirmaymathur.tripod.com/</a><br><br><br><div class="gmail_quote">
On Tue, Dec 1, 2009 at 4:46 AM, Acker, Brad <span dir="ltr"><<a href="mailto:backer@uidaho.edu">backer@uidaho.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<div dir="ltr">
<div dir="ltr"><font color="#000000" face="Arial" size="2">This has been an interesting thread. What I am wondering is do you plan on getting a LEED point for a cool roof? If so and you are not going to use a "pre-approved" product how do you plan to show compliance with whatever emissivity or reflectance values are required? If pretty sure if you just painted your roof white you would need to show some test data per the correct procedures that your roof has the correct values. Anyone have experience with this?</font></div>
<div dir="ltr"><font color="#000000" face="Arial" size="2"></font> </div></div>
<div dir="ltr">
<div><font color="#000000" face="Arial" size="2">
<div><font size="2">Brad in Boise</font></div></font>
<hr>
<font face="Tahoma" size="2"><b>From:</b> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a> on behalf of Abaza Hussein<br><b>Sent:</b> Mon 11/30/2009 3:07 PM<div class="im">
<br><b>To:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br></div><div><div></div><div class="h5"><b>Subject:</b> Re: [Bldg-sim] Why should roofs have high emissivity?<br>
</div></div></font><br></div></div></div><div><div></div><div class="h5">
<div>
<p><font size="2">A key issue is the difference in values between the reflectance and the emissivity of a surface. For example, some white paint has higher emissivity than reflectance which makes it better than aluminum foil.<br>
Hussein Abaza<br>----- Original Message -----<br>From: "Larry Degelman" <<a href="mailto:ldegelman@suddenlink.net" target="_blank">ldegelman@suddenlink.net</a>><br>To: "Brad Painting" <<a href="mailto:bradpainting@gmail.com" target="_blank">bradpainting@gmail.com</a>>, <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br>
Sent: Sunday, November 29, 2009 8:43:05 PM GMT -05:00 US/Canada Eastern<br>Subject: Re: [Bldg-sim] Why should roofs have high emissivity?<br><br>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!<br>
<br>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.<br>
<br>Regards,<br><br>===========================<br>Larry O. Degelman, P.E.<br>Professor Emeritus of Architecture<br>Texas A&M University<br>College Station, TX 77845<br><a href="mailto:ldegelman@suddenlink.net" target="_blank">ldegelman@suddenlink.net</a><br>
===========================<br><br><br>From: Brad Painting<br>Sent: Sunday, November 29, 2009 2:57 PM<br>To: <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br>Subject: [Bldg-sim] Why should roofs have high emissivity?<br>
<br><br>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 low 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><br><br><br>--------------------------------------------------------------------------------<br><br><br>_______________________________________________<br>Bldg-sim mailing list<br><a href="http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org" target="_blank">http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org</a><br>
To unsubscribe from this mailing list send a blank message to <a href="mailto:BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG" target="_blank">BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG</a><br><br>_______________________________________________<br>
Bldg-sim mailing list<br><a href="http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org" target="_blank">http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org</a><br>To unsubscribe from this mailing list send a blank message to <a href="mailto:BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG" target="_blank">BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG</a><br>
_______________________________________________<br>Bldg-sim mailing list<br><a href="http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org" target="_blank">http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org</a><br>
To unsubscribe from this mailing list send a blank message to <a href="mailto:BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG" target="_blank">BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG</a><br></font></p></div></div></div><br>_______________________________________________<br>
Bldg-sim mailing list<br>
<a href="http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org" target="_blank">http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org</a><br>
To unsubscribe from this mailing list send a blank message to <a href="mailto:BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG">BLDG-SIM-UNSUBSCRIBE@ONEBUILDING.ORG</a><br>
<br></blockquote></div><br><br clear="all"><br>-- <br><br>