Re: [TRNSYS-users] Cooling tower (type 51b) controlling

[Shahen Fakhraldin <shahinrkl_7@yahoo.com>]

Hi Jeff,

Even it is not realistic, but I feel there is a lag in the mass flow rate at the outlet 1 of (type 11f) by one timestep, and I think that causes the outlet flow rate from the CT loop being greater than the rated flow of the pump.

However, the problem was solved when I used TESS diverting valve (type 647) instead of (type 11f) and I am not facing any errors or warnings. I didn't change anything in my controlling equations that being used in the W-interpreter (I just added another out for the CT mass fraction)

Thank you so much to remind me to use TESS lib

Kind regards,

Shahen

 

Shahen,

I suggest you use the TRACE command and check to see what the controller is producing for a signal through all iterations of the timestep.  It's very possible that the simulation is not converging and you are seeing the result of that non-convergence.  Make sure you are using a small timestep, have pipes for capacitance, etc.  We control towers all the time but use the tempering valve controller module in the TESS HVAC Library and not an external controller.

 

Jef

On Tuesday, August 19, 2014 5:31 PM, Jeff Thornton <thornton@tess-inc.com> wrote:

Shahen,

I suggest you use the TRACE command and check to see what the controller is producing for a signal through all iterations of the timestep.  It's very possible that the simulation is not converging and you are seeing the result of that non-convergence.  Make sure you are using a small timestep, have pipes for capacitance, etc.  We control towers all the time but use the tempering valve controller module in the TESS HVAC Library and not an external controller.

 

Jeff

 

---
Jeff Thornton
President - TESS LLC
22 N. Carroll Street, Madison WI USA 53703
Office: (608) 274-2577  Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton@tess-inc.com

On 08/19/2014 8:43 am, Shahen Fakhraldin wrote:

Dear TRNSYS users,

 

I am trying to control a cooling tower of absorption chiller by using a three-way valve (type 11f) to mix between the returned water from the chiller and the water coming from the cooling tower (type 51b). 

 

I assumed the range of temperature of mixing 28 - 33 C (over 33 C the flow completely will be through the cooling tower), and I am using (W-interpreter) to produce the mixer (diverter) signal.

 

I am getting strange results where the inlet mass to the chiller (that comes from the cooling tower subsystem) is not equal to the inlet mass of the cooling tower subsystem (that comes from the chiller), even these mass rates exceeded the rated flow rate of the pump of cooling tower subsystem (type 114). Whereas if the diverter signal is fixed (from 0 to 1.0) I do not face this error

 

Did anyone try controlling a cooling tower in TRNSYS?

 

All kinds of help are very much appreciated.

 

Kind regards,

Shahen

 

 

 

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