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<p>Valeria,</p>
<p> All of the models in your simulation are quasi steady state so
they react instantaneously to changes in their inputs. In a real
system, there would be a little bit of a time lag between a
control set point change and when that change can be noticed at a
sensor. The lack of thermal capacitance in your model means that
it reacts unrealistically quickly to changes and thus has a hard
time converging. <br>
</p>
<p> I would recommend that you do two things. First is to add a
thermal storage (buffer) tank into each of your liquid loops. Make
sure that the tank is big enough to store at least one timestep of
liquid. As a side note, I notice that there aren't pumps in your
model. You might consider adding some so that you can perhaps
better control the flow rate in those loops. The second change
would be to make sure that you are using a small time step (on the
order of 1-5 minutes).</p>
<p>kind regards,</p>
<p> David</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 02/19/2020 07:43, Valeria
Badalamenti via TRNSYS-users wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAJtz4G4VDnACFpP4FGQZH5v8Tgb8nmy1+UWcwLTc6d9wLK1sww@mail.gmail.com">
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<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN-US">Dear TRNSYS
Users,</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN-US">I recently
started using TRNSYS and I have a problem with the controls</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN-US">When I
tried to calculate my model, I received this message:</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><i><span
lang="EN-US">“TRNSYS Message 441 : The inputs to the
listed
units have not converged > at this
timestep. The values at the last iteration will be used
and the simulation will proceed.”</span></i></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN-US"> </span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN-US">I'm
modeling a trigenerator (I attach the project screenshot).</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">The hot water,
coming from the exchange with the jacket and Exhaust of the
cogenerator, before
entering the absorber, exchanges heat with steam to reach
the desired
temperature of 90 °C.</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">Upon leaving the
absorber, the hot water returns to the first exchanger by
closing the cycle (magenta
line in the image).</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">The steam is
supplied externally and the steam flow rate varies according
to the outlet hot water
temperature to ensure that this is always constant at the
outlet.</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">To keep the
temperature constant I used Type22 where the input mass flow
rate from Type598
is calculated from the desired Cooling Fluid Outlet
Temperature (red line).</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">But when I feed this
temperature control as input, the model does not work, I
receive the message
441 (see above).</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">If, on the other
hand, I simulate the model without closing the hot water
circuit, the
simulation works.</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">How can I fix
this?</span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN"> </span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">Best regards,</span><span lang="EN-US"></span></p>
<p class="MsoNormal" style="margin:0cm 0cm
0.0001pt;font-size:11pt;font-family:Calibri,sans-serif"><span
lang="EN">Valeria</span></p>
<div><br>
</div>
</div>
<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
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
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