Re: [TRNSYS-users] PID controller to modulate the opening of adamper

["Matt Duffy" <duffy@tess-inc.com>]

Yeonsook,

Knut Erik is right on. You need to add capacitance to your building. As a
default TRNBuild solely considers the capacitance of the zone air. As a
rule of thumb we multiply that by 10 to account for all of the chairs,
plants, arts, crafts, goldfish, etc. in the space. Make sure you
disconnect your feedback loop first (from the PID Controller to the Type56
Building) and simply watch you control signal and the controlled variable,
"FLFTL_1" on an online plotter. Then, you will be able to see if your
controller is turning on correctly, when it is suppose to be turning on.
You can always use the parametrics runs in TRNEdit (ref. TRNSYS Manual
Volume 7) to help tune the P, I, and D coefficients. Also, I have never
used TRNFLOW before, but I am sure it is similar to CONTAM. Make sure you
have a flow path for the damper (or window) frame or housing - other means
of air flow infiltration and not only the window or damper. Those bulk air
flow modeling tools can go hay wire if those aren't included.

Best regards,

Matt Duffy




Best regards,

Matt Duffy
Technical Support Team
Thermal Energy System Specialists
22 N Carroll, Suite 300
Madison, WI  53703
608.274.2577
duffy@tess-inc.com

----- Original Message -----
From: "" <knut.erik.enerstvedt@niva.no>
Sent: Tue, August 11, 2009 2:39
Subject:Re: [TRNSYS-users] PID controller to modulate the opening of adamper

Yeonsook,

I am not sure what excactly causes your problem, but I can give you some
advise on using PID controllers in TRNSYS simulations.

1) Use the controller in mode 0 and with a small time step.
2) Leave the on/off signal (input 3) to 1 unless you need to force the
controlled equipment to be shut down under certain conditions. The
controller will still generate a control signal of 0 if that is what the
PID algorithm predicts.
3) Experiment with the P, I and D coefficients (inputs 7, 8 and 9). If you
use the Proportional term only, the control signal will often oscillate as
the set point is met in one time step but not in the next and so on.
4) Be sure to have enough thermal mass in your system (for example tanks
and pipes) and a sufficiently high thermal capacitance of your building.
That way, the system will react slower to changes in external and internal
conditions, and it will be easier for the controller to stabilize.

Hope this helps.

Kind regards,
Knut Erik




From:
trnsys-users-request@cae.wisc.edu
To:
trnsys-users@cae.wisc.edu
Date:
08/07/2009 07:08 PM
Subject:
TRNSYS-users Digest, Vol 56, Issue 9



----- Message from Yeonsook Heo <yeonsook@gatech.edu> on Fri, 7 Aug 2009
08:29:15 -0700 -----
To:
trnsys-users@cae.wisc.edu
Subject:
[TRNSYS-users] PID controller to modulate the opening of a damper
Dear TRNSYS users,

I am using PID controller to modulate the damper to control natural
ventilation coming to a space through an atrium. The problem is that
control output constantly osciallates from 0 to 1, but never stabilizes at
a certain value between them. I tried to simulate with different time
steps, but the results did not change.

Could you help me what possible problems and solutions are for this
matter?


Thanks,
Yeonsook

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