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</o:shapelayout></xml><![endif]--></head><body lang=FR link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Dear TRNSYS users,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US>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></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>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></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>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></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>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></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>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></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal>Thank you for your help!<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Best regards,<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-family:"Tahoma","sans-serif";color:#58595B'>Marcello Caciolo</span></b><span style='font-family:"Tahoma","sans-serif";color:#58595B'><br></span><span style='font-size:9.0pt;font-family:"Tahoma","sans-serif";color:#58595B'>Responsable Outils et Méthodes d'Analyse Energétique</span><span style='font-family:"Tahoma","sans-serif";color:#58595B'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:gray'><img width=170 height=62 id="Image_x0020_1" src="cid:image001.jpg@01CF2F1B.B84CFF30" alt="cid:image003.jpg@01CD4E08.954D04D0"><br><b><br></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><span style='font-size:9.0pt;font-family:"Tahoma","sans-serif"'><br></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:gray'>Tél.: +33 02 40 41 06 57</span><span style='font-size:9.0pt;font-family:"Tahoma","sans-serif"'><br><a href="mailto:prenom.nom@aximaseitha-gdfsuez.com">marcello.caciolo@cofelyaxima-gdfsuez.com</a></span><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:gray'><o:p></o:p></span></p><p class=MsoNormal><span style='font-family:Webdings;color:#339966'>P</span><span style='font-size:10.0pt;font-family:Webdings;color:#339966'> </span><b><span style='font-size:7.5pt;font-family:"Arial","sans-serif";color:#339966'>Pensez à l'environnement avant d'imprimer ce message</span></b><o:p></o:p></p></div></body></html>