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<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:
10.0pt;font-family:Arial;color:navy">Dear Marcello,<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:
10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">yes, the star-node model work has same limitations especially for extreme geometries and temperature deviations .
<br>
For those cases the star-node work shouldn’t be applied because the results are wrong.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">The “detailed” model is able to handle these extreme cases correctly.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">For ordinary space shapes the star-rnode model does a good job as shown in several comparisons.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">If you aren’t sure if the star-node model performs well for your geometry/temperatures you can check the<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">results with the detailed model based on Gebhart factors.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy">Personally, I simulate 4 surfaces at least in a zone.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><st1:place w:st="on"><st1:City w:st="on"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:
Arial;color:navy">Marion</span></font></st1:City></st1:place><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:
Arial;color:navy"><o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
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<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
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<p class="MsoNormal"><b><font size="1" color="green" face="Arial"><span lang="EN-GB" style="font-size:9.0pt;font-family:Arial;color:green;font-weight:bold">Dipl.-Ing.
</span></font></b><st1:PersonName w:st="on"><b><font size="1" color="green" face="Arial"><span style="font-size:9.0pt;font-family:Arial;color:green;
font-weight:bold">Marion Hiller</span></font></b></st1:PersonName><b><font size="1" color="black" face="Arial"><span style="font-size:8.0pt;font-family:Arial;
color:black;font-weight:bold"><o:p></o:p></span></font></b></p>
<p class="MsoNormal"><b><font size="1" color="black" face="Arial"><span style="font-size:8.0pt;font-family:Arial;color:black;font-weight:bold"><o:p> </o:p></span></font></b></p>
<p class="MsoNormal"><b><font size="1" color="black" face="Arial"><span style="font-size:8.0pt;font-family:Arial;color:black;font-weight:bold">Transsolar Energietechnik GmbH<o:p></o:p></span></font></b></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:black">Curiestraße 2<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:black">70563
<st1:PersonName w:st="on">Stuttgart</st1:PersonName><br>
Telefon: +49 711 67976-0<br>
</span></font><u><font size="1" color="blue" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:blue"><a href="http://www.trnsys.de/">http://www.trnsys.de</a></span></font></u><u><font size="1" color="blue" face="Arial"><span style="font-size:8.0pt;font-family:Arial;
color:blue"><o:p></o:p></span></font></u></p>
<p class="MsoNormal"><u><font size="1" color="blue" face="Arial"><span style="font-size:8.0pt;font-family:Arial;color:blue"><o:p><span style="text-decoration:none"> </span></o:p></span></font></u></p>
<p class="MsoNormal"><b><font size="1" color="green" face="Arial"><span style="font-size:9.0pt;font-family:Arial;color:green;font-weight:bold">Transsolar: KlimaEngineering- Technologien für energieeffizientes Bauen und Nutzerkomfort in Gebäuden</span></font></b><font size="3" color="navy" face="Times New Roman"><span style="font-size:12.0pt;font-family:"Times New Roman";color:navy"><o:p></o:p></span></font></p>
<p class="MsoNormal"><a name="OLE_LINK1"></a><a name="OLE_LINK2"></a><st1:PersonName w:st="on"><b><font size="1" color="green" face="Arial"><span style="font-size:9.0pt;
font-family:Arial;color:green;font-weight:bold">Stutt</span></font></b><b><font size="1" color="green" face="Arial"><span style="font-size:9.0pt;font-family:Arial;
color:green;font-weight:bold">gart</span></font></b></st1:PersonName><b><font size="1" color="green" face="Arial"><span style="font-size:9.0pt;font-family:Arial;
color:green;font-weight:bold">
– München – New York – Paris <o:p></o:p></span></font></b></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:black">Geschäftsführer :Diplom-Ingenieur
<st1:PersonName w:st="on">Matthias Schuler</st1:PersonName>, Diplom-Ingenieur <st1:PersonName w:st="on">
Thomas Auer</st1:PersonName>, Diplom-Physiker <st1:PersonName w:st="on">Stefan Holst</st1:PersonName>, Diplom-Betriebswirt
<st1:PersonName w:st="on">Dieter Schnelle</st1:PersonName><o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:black">Eingetragen beim Amtsgericht
<st1:PersonName w:st="on">Stuttgart</st1:PersonName> HRB 23347, <o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size:
8.0pt;font-family:Arial;color:black">Steuernummer: 99073/00911,USt-IdNr.: DE 152272639<o:p></o:p></span></font></p>
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<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:
10.0pt;font-family:Arial;color:navy"><o:p> </o:p></span></font></p>
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<p class="MsoNormal"><b><font size="2" face="Tahoma"><span style="font-size:10.0pt;
font-family:Tahoma;font-weight:bold">Von:</span></font></b><font size="2" face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma">
<st1:PersonName w:st="on"><st1:PersonName w:st="on">trnsys-users</st1:PersonName>-bounces@cae.wisc.edu</st1:PersonName> [mailto:<st1:PersonName w:st="on"><st1:PersonName w:st="on">trnsys-users</st1:PersonName>-bounces@cae.wisc.edu</st1:PersonName>]
<b><span style="font-weight:bold">Im Auftrag von </span></b><st1:PersonName w:st="on">marcello.caciolo@cofelyaxima-gdfsuez.com</st1:PersonName><br>
<b><span style="font-weight:bold">Gesendet:</span></b> Freitag, 21. Februar 2014 15:54<br>
<b><span style="font-weight:bold">An:</span></b> <st1:PersonName w:st="on"><st1:PersonName w:st="on">trnsys-users</st1:PersonName>@cae.wisc.edu</st1:PersonName><br>
<b><span style="font-weight:bold">Betreff:</span></b> [TRNSYS-users] Long wave radiation heat exchange and number of surfaces</span></font><font size="3" face="Times New Roman"><span style="font-size:12.0pt;font-family:"Times New Roman""><o:p></o:p></span></font></p>
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<p class="MsoNormal"><font size="2" face="Calibri"><span style="font-size:11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="FR" style="font-size:
11.0pt">Dear TRNSYS users,<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="FR" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt">I have a very simple non-geometrical type 56 model with one zone with two surfaces: one boundary surface of 40 m2 and an external surface of 400 m2. External condition
and boundary temperature are held constants.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt">When I plott surface temperatures and heat exchange between the two surfaces, I found a very large long wave radiation exchange between the two surfaces.
<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt">By hand calculation (Q=sigma S (T1^4 – T2^4), whit S = area of the little surface), I found that the value given of heat exchange by radiation by TRNSYS is about
ten times larger than what I expected. Indeed, it seems that value given by TRNSYS is near to the value given by the same equation but considering the largest surface area.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt">However, if I split the external surface in two surfaces of half the area, the value calculated by TRNSYS is reduced of about 7 times. If I split again these surfaces,
radiation exchange continue to drop but more slightly, tending to a value near the one calculated by hand.
<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt">My question is : have you already found the same behavior? Is there a recommendation to define at least three surfaces in a zone in order to calculate properly
heat exchange by radiation?<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="EN-US" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="FR" style="font-size:
11.0pt">Thank you for your help!<o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="FR" style="font-size:
11.0pt"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font size="2" face="Calibri"><span lang="FR" style="font-size:
11.0pt">Best regards,<o:p></o:p></span></font></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><font size="2" color="#58595b" face="Tahoma"><span lang="FR" style="font-size:11.0pt;
font-family:Tahoma;color:#58595B;font-weight:bold">Marcello Caciolo</span></font></b><font color="#58595b" face="Tahoma"><span lang="FR" style="font-family:Tahoma;color:#58595B"><br>
</span></font><font size="1" color="#58595b" face="Tahoma"><span lang="FR" style="font-size:9.0pt;font-family:Tahoma;color:#58595B">Responsable Outils et Méthodes d'Analyse Energétique</span></font><font color="#58595b" face="Tahoma"><span lang="FR" style="font-family:Tahoma;color:#58595B"><o:p></o:p></span></font></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><font size="2" color="gray" face="Arial"><span lang="FR" style="font-size:10.0pt;font-family:
Arial;color:gray"><img border="0" width="170" height="62" id="Image_x005f_x0020_1" src="cid:image001.jpg@01CF32EF.D4DBC960" alt="cid:image003.jpg@01CD4E08.954D04D0"><br>
<b><span style="font-weight:bold"><br>
</span></b>Cellule Efficacité Energétique et Environnementale - Pôle Projets et Réalisations<br>
46 Boulevard de la Prairie au Duc<br>
BP 40119 - 44201 Nantes Cedex 02</span></font><font size="1" face="Tahoma"><span lang="FR" style="font-size:9.0pt;font-family:Tahoma"><br>
</span></font><font size="2" color="gray" face="Arial"><span lang="FR" style="font-size:10.0pt;font-family:Arial;color:gray">Tél.: +33 02 40 41 06 57</span></font><font size="1" face="Tahoma"><span lang="FR" style="font-size:9.0pt;font-family:Tahoma"><br>
<a href="mailto:prenom.nom@aximaseitha-gdfsuez.com">marcello.caciolo@cofelyaxima-gdfsuez.com</a></span></font><font size="2" color="gray" face="Arial"><span lang="FR" style="font-size:10.0pt;font-family:
Arial;color:gray"><o:p></o:p></span></font></p>
<p class="MsoNormal"><font size="2" color="#339966" face="Webdings"><span lang="FR" style="font-size:11.0pt;font-family:Webdings;color:#339966">P</span></font><font size="2" color="#339966" face="Webdings"><span lang="FR" style="font-size:10.0pt;
font-family:Webdings;color:#339966">
</span></font><b><font size="1" color="#339966" face="Arial"><span lang="FR" style="font-size:7.5pt;font-family:
Arial;color:#339966;font-weight:bold">Pensez à l'environnement avant d'imprimer ce message</span></font></b><span lang="FR"><o:p></o:p></span></p>
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