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Vincent,<br>
When you perform an energy balance on a tank, you need to take
into account its change in temperature between the beginning and the
end of the simulation (output 7 of your Type4). If the tank ends up
hotter at the end of the simulation than it was at the beginning, it
has stored some energy. If it ends up colder, then it has given up
some energy. I would imagine that with 10 nodes, there is some
stratification developing in the tank that is not modeled when you
have a fully mixed tank (1 node)<br>
Best,<br>
David<br>
<br>
<br>
<div class="moz-cite-prefix">On 10/25/2012 09:40, PARTENAY Vincent
wrote:<br>
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<p class="MsoNormal">Dear all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US">Typ4a (Storage tank)
allows to model a stratified tank with several temperature
nodes. The problem I noticed is that the energy balance of
both sides on the tank can vary depending on the chosen
timestep :<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">In the attached file, a
simplified example, the tank is coupled to an energy
production and energy consumption model (very simple in an
equation). Thermal losses of the tank is set to zero.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">When I run a simulation
with one node (1m height for 0.5m3) for the tank and a
timestep of 0.1hr, I get the same energy on both side (see
plotter “”Power&NRJ”, Esource = 2659kWh and Eload =
2666kWh), slight difference maybe explained by initial
charging period to setpoint temperature.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">When I run it in the
same conditions but with 10 nodes (each 0.1m), these two
energy are different ! While I still have 2666kWh for Eload
I have 3146kWh !<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">When I run it again
reducing the timestep from 0.1hr to 0.001 hr, still with 10
nodes, I get 2666kWh, the energy balance is ok…<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">So, my question is : is
it necessary to check before every bigger simulation (that
can include lots of tank models) the energy balance of this
model for one defined timestep and boundary conditions to
the model or is there some rules to predefine adapted
discretisation for one given timestep ?<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"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span
style="font-family:"Verdana","sans-serif";
color:black">Vincent PARTENAY<o:p></o:p></span></b></p>
<p class="MsoNormal"><span
style="font-size:8.0pt;font-family:"Verdana","sans-serif";color:black">Energies
Renouvelables - Département ESE</span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";color:#1F497D"><o:p></o:p></span></p>
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<p class="MsoNormal"><b><span
style="font-family:"Verdana","sans-serif";
color:#0000A1">Centre Scientifique et Technique du
Bâtiment<o:p></o:p></span></b></p>
<p class="MsoNormal"><span
style="font-size:8.0pt;font-family:"Verdana","sans-serif";color:black">290
Route des Lucioles BP 209 – F 06904 Sophia Antipolis Cedex<o:p></o:p></span></p>
<p class="MsoNormal"><span
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