Valeria,
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.
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).
kind regards,
David
Dear TRNSYS Users,
I recently started using TRNSYS and I have a problem with the controls
When I tried to calculate my model, I received this message:
“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.”
I'm modeling a trigenerator (I attach the project screenshot).
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.
Upon leaving the absorber, the hot water returns to the first exchanger by closing the cycle (magenta line in the image).
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.
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).
But when I feed this temperature control as input, the model does not work, I receive the message 441 (see above).
If, on the other hand, I simulate the model without closing the hot water circuit, the simulation works.
How can I fix this?
Best regards,
Valeria
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-- *************************** 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 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com