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Devin,<br>
The default value of the zone capacitance is 1.007*1.2*ZoneVolume.
It accounts only for the capacitance of the air in the zone and does
not account for any furnishings or zone contents. I typically modify
the capacitance to be about 5 times the default value (up to 10
times for zones that have a LOT of stuff in them like a library, a
warehouse, or (unfortunately) my basement). Whether you leave the
default value or whether you increase it, there is still thermal lag
from the concrete but that lag is heavily influenced by the heat
transfer coefficient between the zone air and the concrete wall.<br>
Best,<br>
David<br>
<br>
<br>
On 6/26/2011 10:32, Devin Rohan wrote:
<blockquote
cite="mid:BANLkTin5+0NFWLzfQ2aHYvfr-HbO7a3=7A@mail.gmail.com"
type="cite">I have a single zone office with a concrete slab and
non-massive walls. I only seem to get good agreement between
TRNSYS and a 1D finite difference model I built when I increase
the Zone Air capacitance into the thousands (4000-6000 kJ/K).
Other wise, TRNSYS's air temperature varies wildly and
unrealistically with the ambient temperature and there's no
thermal lag from the concrete. Is this high of value for the zone
air capacitance ok?<br clear="all">
<br>
-- <br>
Devin M. Rohan, LEED Green Associate<br>
Purdue University <br>
Civil/Architectural Engineering<br>
<a moz-do-not-send="true" href="mailto:drohan@purdue.edu"
target="_blank">drohan@purdue.edu</a><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>
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