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--></style></head><body lang=EN-CA link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='mso-fareast-language:EN-US'>If you assume that the cavity has a very high infiltration rate (which seems to be the case here) and you can accept the assumption that radiative transfer with the ground is negligible, a simpler option would be to remove the cavity from the model. <o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>The floor above the cavity would become an outside surface, you would just have to make sure it does not receive solar radiation. You can do that by forcing its exterior absorptance to 0 or by defining a special orientation for which you do not use automatic solar radiation calculation in Type 56 (and you leave the inputs unconnected with constant 0 value). You could also define that outside surface as a boundary wall with a boundary temperature equal to the ambient temperature. <o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>This is (I think) acceptable if the floor is reasonably well insulated, so that the assumption on the cavity temperature has a minor impact on the model. One advantage is that it saves you from having to use a ground coupling model.<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Of course, if you are specifically interested in what is happening in the cavity, then David’s suggestion to model it as a zone and to model infiltration (rather than assuming a constant rate) is what I would choose. And I think you would have to add a ground coupling model, to be consistent with the level of detail in the rest of the model. <o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Michaël Kummert<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'>Polytechnique Montréal<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US>From:</span></b><span lang=EN-US> David BRADLEY via TRNSYS-users <trnsys-users@lists.onebuilding.org> <br><b>Sent:</b> June 11, 2021 10:33<br><b>To:</b> TRNSYS users mailing list at OneBuilding.org <trnsys-users@lists.onebuilding.org><br><b>Cc:</b> David BRADLEY <d.bradley@tess-inc.com><br><b>Subject:</b> Re: [TRNSYS-users] How to model a cavity zone under a building<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p>Seyedmostafa,<o:p></o:p></p><p> You're on the right track. At least your method is the same that I used when I was modeling a similar situation. In my case there was a thin vinyl skirt around the building so I used its thermal resistance for my massless walls. I think the way to assess the infiltration into the cavity is to couple the Type56 thermal model either with CONTAM (using Type97 or Type98) or with TRNFlow. Both are designed to estimate airflow between pressure nodes in buildings.<o:p></o:p></p><p>kind regards,<o:p></o:p></p><p> David<o:p></o:p></p><p><o:p> </o:p></p><p><o:p> </o:p></p><div><p class=MsoNormal>On 06/11/2021 05:06, Seyedmostafa Mousavi via TRNSYS-users wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal>Hi all,<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Hope you are very well.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>I’m modelling a cabin in SketchUp using the TRNSYS3D plugin. In the real cabin structure, several steel posts were used to elevate the cabin and separate its floor from the ground. The air easily flows in this cavity under the cabin, see <b>Fig. 1</b>. To model the cavity, I’ve considered a bottom zone in which the walls were defined as <i>Massless Layers</i> with R-value of 0.044 h m^2 K/ kJ (equal to the air gap), see <b>Fig. 2</b>.<o:p></o:p></p><p class=MsoNormal>However, I’m not sure if this modelling process is correct. Do we have any option in TRNSYS to consider such cavity under buildings?<o:p></o:p></p><p class=MsoNormal>BTW, if this model is correct, how should I calculate the infiltration rate for the cavity section? Any idea is highly appreciated.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Thanks a lot for your help.<o:p></o:p></p><p class=MsoNormal style='text-autospace:none'><b><span lang=EN-AU style='font-size:10.0pt;color:#002060'> </span></b><o:p></o:p></p><p class=MsoNormal style='text-autospace:none'><b><span lang=EN-AU style='font-size:10.0pt;color:#002060'>Warmly,</span></b><o:p></o:p></p><p class=MsoNormal style='text-autospace:none'><b><span lang=EN-AU style='font-size:10.0pt;color:#002060'>Seyedmostafa Mousavi</span></b><o:p></o:p></p><p class=MsoNormal style='text-autospace:none'><span lang=EN-AU style='font-size:10.0pt;color:#002060'>The University of Melbourne, Victoria 3010 Australia</span><span lang=EN-AU> </span><o:p></o:p></p><p class=MsoNormal style='text-autospace:none'><b><span lang=EN-AU style='font-size:10.0pt;color:#002060'>E: </span></b><span lang=EN-AU style='font-size:10.0pt;color:#002060'><a href="mailto:sm.mousavi@unimelb.edu.au">sm.mousavi@unimelb.edu.au</a> </span><o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal><br><br><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>TRNSYS-users mailing list<o:p></o:p></pre><pre><a href="mailto:TRNSYS-users@lists.onebuilding.org">TRNSYS-users@lists.onebuilding.org</a><o:p></o:p></pre><pre><a href="http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org">http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org</a><o:p></o:p></pre></blockquote><pre>-- <o:p></o:p></pre><pre>***************************<o:p></o:p></pre><pre>David BRADLEY<o:p></o:p></pre><pre>Principal<o:p></o:p></pre><pre>Thermal Energy Systems Specialists, LLC<o:p></o:p></pre><pre>3 North Pinckney Street - suite 202<o:p></o:p></pre><pre>Madison, WI 53703 USA<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>P:+1.608.274.2577<o:p></o:p></pre><pre><a href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre><a href="http://www.tess-inc.com">http://www.tess-inc.com</a><o:p></o:p></pre><pre><a href="http://www.trnsys.com">http://www.trnsys.com</a><o:p></o:p></pre></div></body></html>