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Leen,<br>
The reason that thick, highly insulated walls give you a problem
is that TRNBuild generates the first 20 coefficients of the transfer
function that describes the thermal response of the wall. The
coefficients correspond to discreet intervals of time starting with
the present and moving backwards by steps of the timebase specified
in TRNBuild. The default is an hour so it is my understanding that
TRNBuild looks back at 20 hours worth of transfer function
coefficients to determine whether the numerical stability of the
wall model has been met. In very massive walls, 20 hours might not
be a long enough time interval to adequately describe the wall's
response. You can try to increase the wall timebase to 2 hours in
order to extend how far back the wall's response is considered.
However, in my experience, this can cause problems with the less
massive walls in the same project (which sometimes have to be
changed over to massless walls since their response time is now too
short to be adequately represented with a 2 hour timebase.<br>
Best,<br>
David<br>
<br>
<br>
On 4/14/2012 17:27, leen peeters wrote:
<blockquote
cite="mid:CAB_-mWN2vPPAfZSdgzUwm4FxCyP1UVdja-QSAaXYC0z68Vi9QA@mail.gmail.com"
type="cite">
<div>Dear all,</div>
<div> </div>
<div>I am trying to model an old house which will be imporved to a
very good house (<a class="moz-txt-link-abbreviated" href="http://www.zehr">www.zehr</a> .be). The existing brick walls consist
of 33 cm of brick, no air cavity or insulation. One wall will be
packed with 6cm VIP, the remainder will be packed with a 30 cm
layer of insulation (lanba of 0.038 W/mK). </div>
<div>However modeling that, I ran into problems with the stability
of the transfer function, shoudl that I had to tune my
capacities and densities in order to end up with something that
was accepted for calculating the transferfunction. </div>
<div> </div>
<div>Can anyone explain me the logic of these warming messages and
the reason why thick highly insulated walls cause an issue? I
trid splitting one layer into two, but that did not resolve the
problems...</div>
<div> </div>
<div>leen</div>
<br>
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<br>
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<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:+1.608.274.2577
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.tess-inc.com">http://www.tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.trnsys.com">http://www.trnsys.com</a></pre>
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