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On 7/12/2010 11:02, Julie Lestrade wrote:
<blockquote
cite="mid:367967683.197171278950571350.JavaMail.root@secure3.wizteamwork.com"
type="cite"><font size="2"><font size="2"><span
style="color: rgb(0, 0, 0);"><span style="font-family: Arial;">Hello </span></span></font><font
color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;">Mariëlle <br>
<br>
Thank you for your quick answer.<br>
<br>
1) For this question I do understand this in principle but I don't see
how/when TRNSYS is considering it. By the way, what about the
capacitance ? is the default value calculated by TRNSYS a good one ? <br>
</span></font></font></blockquote>
TRNSYS uses the conduction transfer function method to compute the
energy transfer through the wall. I would recommend looking at some of
the archives of this mailing list for detailed explanations. However,
to answer your direct question, the values of capacitance, density, and
thermal conductivity of the various materials in the default libraries
are pretty good. It is not too hard to double check them online if you
are concerned. <br>
<br>
For the most part, they do NOT consider thermal bridging effects but
are for the monolithic material. the TESS layer library includes some
equivalent materials for typical (US) stud wall constructions. These
are equivalent materials that account for the ratio of wooden stud to
insulated cavity. You can do the same for other configurations of
materials if you need.<br>
<blockquote
cite="mid:367967683.197171278950571350.JavaMail.root@secure3.wizteamwork.com"
type="cite"><font size="2"><font color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;">2) I
understood I could do that, but it's calculated by default and I don't
particularly know the solar absorbance of the material. So I was
wondering if the calculation was alright ?<br>
</span></font></font></blockquote>
I would recommend that you run the building and look at energy use
twice, once with a low estimate of the solar absorptance and once with
a high estimate. That way you will be able to determine the overall
sensitivity to that particular parameter and know whether it is worth
spending time looking for a better estimate than the default.<br>
<blockquote
cite="mid:367967683.197171278950571350.JavaMail.root@secure3.wizteamwork.com"
type="cite"><font size="2"><font color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;">5) Yes I'm
adding a question here : for the ground definition, it is important to
set the temperature of the earth below. By default it's 15°C. Does
anybody know for which region of the world this is true ? <br>
</span></font></font></blockquote>
if you don't know any better, the undisturbed deep earth ground
temperature is approximately equal to the location's annual average air
temperature. However, that does not account for the long term
accumulation or reduction of energy in the soil directly underneath the
building due to coupling with the building's conditioning. If you are
using TRNSYS 17, you might look at Type49 (slab on grade); a good bit
of research has gone into this area recently and that component (while
slow) does a very good job of calculating what the below grade
temperature is as a function of time.<br>
<br>
Best,<br>
David<br>
<br>
<br>
-- <br>
<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:bradley@tess-inc.com">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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