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Re: [TRNSYS-users] Determining umax in feedback controller

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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