[TRNSYS-users] Determining umax in feedback controller

[David BRADLEY]

Rambod,
   I assume that by umin and umax, you mean inputs 4 and 5. If that is 
the case then this inputs simply define the range of the controller's 
output. If you want to control a pump between fully off and fully on at 
its rated flow rate then you might choose 0 and 1 for your limits (as in 
the SDHW-Feedback example). If you wanted the controller to set the flow 
rate directly then you would set umin to 0 and umax to the maximum 
allowable flow rate.

   As for the issue of the temperature being above 120C when flow rate 
is zero, that seems quite possible since collectors can reach very high 
"stagnation" temperatures when there is no flow through them. It may be 
that under those circumstances, your controller cannot meet 120C at any 
flow rate so hits its limit on the number of times that it can change 
control decisions before it "sticks" (oscillation limit parameter).
Kind regards,
  David


On 1/16/2011 16:49, Rambod Rayegan wrote:
>
> Dear TRNSYS users,
>
> I created a TRNSYS file to simulate the performance of a flat plate 
> collector. In this file I used a feedback controller to set the 
> collector's output temperature on 120 °C.I checked the TRNSYS example 
> "SDHW-Feedback controller" and I chose umin and umax equal to 0 and 1 
> respectively.
>
> When I check the results I see that in some time steps temperature is 
> higher than 120 °C while flow rate is zero. BY changing umax in 
> feedback controller the results are being modified slightly but I 
> don't know how I can find the optimum umax.
>
> Actually I am not sure that changing umax will solve the problem.
>
> Attached to this email you can find a copy of my file.
>
> Thank you.
>
> Rambod
>
>
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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