<div>Johannes,</div>
<div> </div>
<div>as soon as you decrease the distance between the pipes, you come closer to the limits set regarding the modeling of the heat transfer in the direction of the water flow (direction z in the mathematical model). The stability of that model requires that you achieve a certain boundary condition, which is a.o. function of the thermal resistance of the water-pipe-inter pipe distance. In order to ensure these boundary conditions are satisfied the ratio of pipe outside diameter over pipe distance < 0.2 AND the ratios of layer thickness over pipe distance > 0.3. The 0.024-value you received for the minimum layer thickness comes from this limitation. I assume the extra measure is invoked once you come close to the 0.2-limit.</div>
<div>As soon as you take 0.1 for the pipe distance, you can again select 0.008 m for layer thickness ...</div>
<div>Playing around with conductivity or capacity does not help, as the measure seems to be implemented through the above limits only ....</div>
<div> </div>
<div>Leen<br><br><br></div>
<div class="gmail_quote">On Mon, Dec 12, 2011 at 1:48 PM, Schrade, Johannes <span dir="ltr"><<a href="mailto:Johannes.Schrade@ibp.fraunhofer.de">Johannes.Schrade@ibp.fraunhofer.de</a>></span> wrote:<br>
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<p class="MsoNormal">Dear TRNSYS users,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I have some problems with the active layer module of TRNBLD, which I used for modeling a floor heating system.<u></u><u></u></p>
<p class="MsoNormal">The active layers, which should be displayed in the model, are defined as following:<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Layer 1:<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe spacing: 24 cm<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe outside diameter: 16 mm<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe wall thickness: 2 mm<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Layer 2:<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe spacing: 8 cm<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe outside diameter: 16 mm<u></u><u></u></p>
<p><u></u><span style="FONT-FAMILY:Symbol"><span>·<span style="FONT:7pt 'Times New Roman'"> </span></span></span><u></u>Pipe wall thickness: 2 mm<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">By specifying the thicknesses of the layers adjacent to the active layers, the following curiosity appeared.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">For case 1, I set the thickness of the layer above the active layer to 73 mm, which is greater than 0.3 times the pipe spacing, and I set the layer below to 0.5 times the pipe outside diameter (requirements taken from manual TRNSYS 17, 5-187, table). This step had worked pretty good and the simulation was running without any problems.<u></u><u></u></p>
<p class="MsoNormal">In a second step, I revised the model and included the second active layer into the TRNBLD model. As the floor screed should be identical for both cases, I tried to define the thicknesses of the adjacent layers the same way as I did it in case 1. But when I tried to reduce the thickness of the adjacent layer below, the following warning appeared: “thickness must be in the range of 0.024 to 1.0”.<u></u><u></u></p>
<p class="MsoNormal">In order to understand this warning I had a closer look to the manual of TRNBLD. On page 5-58 (TRNSYS 17) I found a remark that both layers adjacent to the active layer must be greater than 0.3 times pipe spacing. This would explain, why the warning appears, but I do not understand, why the first case should be unproblematic, as the required minimum thickness in this case should be 72mm and why this is not mentioned in the mathematical description.<u></u><u></u></p>
<p class="MsoNormal">Does anyone has an idea, what could be the reason behind that, or might this be a known or unknown bug? If this requirement dependent on the pipe spacing should be really used for both layers, this would mean that extremely thick floor screeds of +15cm are necessary to model a floor heating system with a pipe spacing of 24 cm. This sounds absolutely unrealistic. <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Hoping for some help,<u></u><u></u></p>
<p class="MsoNormal">Kind regards,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Johannes Schrade<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<p style="MARGIN-BOTTOM:6pt;MARGIN-LEFT:3pt;MARGIN-RIGHT:3pt" class="MsoNormal"><b><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt">Johannes Schrade</span></b><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt"><br>
Abteilung Wärmetechnik<u></u><u></u></span></p>
<p style="MARGIN-BOTTOM:6pt;MARGIN-LEFT:3pt;MARGIN-RIGHT:3pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt">Fraunhofer-In</span><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt" lang="DE">stitut für Bauphysik<br>
Nobelstr. 12<br>70569 Stuttgart<u></u><u></u></span></p>
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<p style="MARGIN-BOTTOM:6pt;MARGIN-LEFT:3pt;MARGIN-RIGHT:3pt" class="MsoNormal"><b><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt">Johannes Schrade</span></b><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt"><br>
Department Heat Technology <u></u><u></u></span></p>
<p style="MARGIN-BOTTOM:6pt;MARGIN-LEFT:3pt;MARGIN-RIGHT:3pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt">Fraunhofer Institute for Building Physics<br>Nobelstr. </span><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:9pt" lang="DE">12<br>
70569 Stuttgart, Germany<u></u><u></u></span></p>
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