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<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Hi Vikram,
</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2>The latest release of EnergyPlus (v. 1.1.1) added a model for
light pipes, i.e. tubular daylighting devices. The model is fully
described in the documentation that comes with the program.
</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Just to give you an
idea in brief, light pipes can add both solar gains and conductive/convective
gains to the space below. The solar gains are calculated by analyzing the
multiple internal reflections of the incident beam, sky, and
ground radiation entering the pipe. The amount of radiation
transmitted depends on the incident angle, reflectivity, and geometry of the
pipe, and on the properties of the glazing at either end of the pipe.
Fortunately, all of this is </FONT></SPAN><SPAN class=197364717-22012004><FONT
face=Arial size=2>entirely handled by the program. </FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004></SPAN><SPAN class=197364717-22012004><FONT
face=Arial size=2>The conductive/convective gains, o<SPAN
class=197364717-22012004><FONT face=Arial size=2>n the other
hand,</FONT></SPAN> require the user to enter an effective thermal
resistance (R-value) between the top and bottom of the light pipe. The
problem is knowing what R-value to use. </FONT></SPAN><SPAN
class=197364717-22012004><FONT face=Arial size=2>Very little research has
been done on this area of the problem (as of about 1 year ago--the last time I
looked). I have only found one paper that analyzes the
conductive/convective behavior of light pipes: </FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2><SPAN
class=197364717-22012004><FONT face=Arial size=2>Harrison, S. J., McCurdy, G.
G., Cooke, R. "Preliminary Evaluation of the Daylighting and Thermal
Performance of Cylindrical Skylights", Proceedings of International Daylight
Conference, Ottawa, Canada, 1998, pp. 205-212.</FONT></SPAN></FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>They
repor</FONT></SPAN><SPAN class=197364717-22012004><FONT face=Arial size=2>t an
average thermal resistance of 0.279 m2 K/W for a pipe measuring 1.83 m by 0.33
m. </FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Hope this
helps!</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Peter Graham
Ellis</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>National Renewable
Energy Laboratory</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Center for Buildings
and Thermal Systems</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>1617 Cole
Boulevard</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2>Golden, Colorado
80401-3393</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial
size=2>303-384-7443</FONT></SPAN></DIV>
<DIV><SPAN class=197364717-22012004><FONT face=Arial size=2><A
href="mailto:peter_ellis@nrel.gov">peter_ellis@nrel.gov</A></FONT></SPAN></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Vikram Sami
[mailto:Vikram@ensargroup.com]<BR><B>Sent:</B> Wednesday, January 21, 2004 4:04
PM<BR><B>To:</B> BLDG-SIM@gard.com<BR><B>Subject:</B> [BLDG-SIM] Heat gain from
light pipes<BR><BR></FONT></DIV>
<DIV><SPAN class=351410023-21012004>Hi,</SPAN></DIV>
<DIV><SPAN class=351410023-21012004>I have a question about light
pipes. We are using then for a project, and I was wondering if there was
any way to calculate the heat transmitted to the space below through the
pipes.</SPAN></DIV>
<DIV><SPAN class=351410023-21012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=351410023-21012004>Thanks</SPAN></DIV>
<DIV><SPAN class=351410023-21012004><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=351410023-21012004>
<P><FONT size=2><FONT color=#800000 size=3>Vikram Sami</FONT><BR></FONT><FONT
size=1><EM><BR><FONT size=2>ENSAR Group, Inc.<BR>2305 Broadway<BR>Boulder, C0
80304<BR>(303).449.5226 Tel<BR>(303).449.5276
Fax<BR><BR></FONT></P></EM></FONT></SPAN></DIV><PRE>
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