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<p>Jim,</p>
<p> It is normal that Type997 is slow; it is solving a finite
difference problem for the entire ground field. The model will run
particularly slowly at the beginning of your simulation but will
increase in solving speed to some extent as it gets farther in
(and as the changes in the ground field from one timestep to the
next diminish). You can speed the model up to some extent by
increasing the size of your smallest soil node and increasing the
value of the node size multiplier. The point of Type997, though it
to provide a rigorous and stable solution. Type952 models a single
buried pipe rather than a network of pipes. We use it (or its
twin-conductor cousin) to model the runouts to and from the ground
field.</p>
<p>You have to be a bit careful if if your ground field is actually
buried air ducts rather than pipes containing a liquid. Both
Type952 and 997 make the assumption that the thermal properties
(density, specific heat, etc.) are constant over the working
temperature range, which isn't always a great assumption with air.
This is particularly true if there is a chance that the water
vapor in the air condenses as it goes through the ground field.
There are models available (Transsolar's Type460 for example) that
are designed to model underground hypocausts such as the one it
sounds like you are modeling. If indeed air is your working fluid,
I would recommend using one of those models in place of either 997
or 952.<br>
</p>
<p>kind regards,</p>
<p> David</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 09/09/2021 12:45, dimitris soukoulis
via TRNSYS-users wrote:<br>
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<blockquote type="cite"
cite="mid:VI1PR08MB35030D1749DAB500167AC7A6A7D59@VI1PR08MB3503.eurprd08.prod.outlook.com">
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<p class="MsoNormal"><span lang="EN-US">Hello everybody,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I am simulating a
multizone building with four separately air-conditioned
zones (apartments). So far I was working with the 954 air
source heat pump ( four of them. One for each zone ) but my
goal was to have a ground source heat pump system connected
to the building. I tried using the type 997 Horizontal
ground heat exchanger and connect its outlet flowrate to the
inlet of each air source heat pump, but my simulation
became extremely slow. I am now experimenting with the type
952 buried horizontal pipe, setting the average surface
temperature equal to the annual average ambient temperature.
I also want to change the working fluid from water (default)
to air so I can directly feed it into the 954 air source
heat pump. This set-up is significantly faster than before,
but I am having doubts about its correctness. Any idea,
suggestion or advice will be greatly appreciated.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">And one last question.
Is there any standard way of calculating a heat pumps air
flow rate, or is it just trial and error ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks a lot in advance.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Kind regards ,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Jim Soukoulis <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">National Technical
University of Athens.</span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Στάλθηκε από την <a
href="https://go.microsoft.com/fwlink/?LinkId=550986"
moz-do-not-send="true">
Αλληλογραφία</a> για τα Windows</p>
<p class="MsoNormal"><o:p> </o:p></p>
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<br>
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<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI 53703 USA
P:+1.608.274.2577
<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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