[TRNSYS-users] PID controller problem - TRNSYS Message 315

[Michaël Kummert]

the likely cause of the warning is that you are using the PID controller
(Type 23) in “real time” mode (Mode 0) and that you built your project by
adding some of the controlled components (components which use the PID
output) after you added the PID to the project. 

In Mode 0, the controller calculates its output at each iteration within a
given time step, but only applies the result (i.e. updates its output) after
convergence has been reached, so that the calculated control signal is
applied at the next time step, not at the current time step.

 

When you use that mode, if the PID is placed before the component it
controls in the “calling order” of TRNSYS, the controlled component will
receive a non-updated output (which is exactly what you want). TRNSYS warns
you about it, and the message is clear that it’s not necessarily an error
but it’s unusual – and it could be an error in some specific cases. 

 

In this case the behaviour is not an error, so you can safely ignore the
warning, but if you want to suppress it, the easy way is to make sure that
the PID controllers are located after all components they control in the
input file. You can change that in “Component Order” in the Studio (Gear
icon or Assembly > Settings, then Component Order). Just drag all PIDs below
the components they control. By default, components are placed in that list
in the order you add them to the project, so this may explain that some
early versions of your project were not causing any warning (because the
PIDs were added after the components using them).

 

Michaël Kummert

Polytechnique Montréal

 

 

From: Giulio Tonellato via TRNSYS-users <trnsys-users at lists.onebuilding.org>

Sent: February 25, 2023 14:40
To: trnsys-users at lists.onebuilding.org
Cc: Giulio Tonellato <g.tonellato at hotmail.com>
Subject: Re: [TRNSYS-users] PID controller problem - TRNSYS Message 315

 

I am having the same exact issue.

It came up super randomly  when activating my air handling unit that is
heating up the air. I say randomly because it never appeared before even
with the AHU on. 

The PID controllers control radiators with a certain air set temperature in
the rooms.

Only thing I changed  lately was the pipes’ geometry before and after
radiators, but now changing it back does not seem to solve the problem.

Did you solve it in the end? Anyone knows about this?

 

Regards,

 

Giulio

 

The message was by Mariam Elnour
Mon Aug 6 07:38:12 PDT 2018

 

Dear TRNSYS users,

 

     I am having a problem with PID controllers performance . I tried
modifying the components order however I still get the same warnings on all
PID controllers units used in the project. The TRNSYS Message    315 is as
follows,

 

 

"The TRNSYS processor has reported a potential problem with the connections
in your input file. In version 16, there is a very specific calling order
after convergence has been reached at each timestep. One of your connections
flows against this calling order - for example you may have the output of an
integrator connected as an input to a standard component (one that is being
called iteratively at each timestep). While this is not technically an ERROR
- it may cause incorrect values to be passed to the component. For example,
the input to an iterating component from an integrator will be from the
previously converged timestep and not the current timestep. Refer to the
TRNSYS Manual - Volume 1 - for more information on the calling order for
TRNSYS components"

 

 

Is there a way to solve this issue?

 

 

Thank you.

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