Re: [TRNSYS-users] "Advanced" tempering valve

[David BRADLEY <d.bradley@tess-inc.com>]

Damien,
  The tempering valve controller model is quite a simple equation involving the ratio of temperatures. It is derived from an energy balance (the sum of all the m_dot*Cp*T terms). I would think that if you know the flow rate and temperature of the water that is being added between steps 1 and 2, you could resolve the energy balance and determine a new control algorithm for the tempering valve.
Best,
 David
 

On 5/14/2013 01:42, Damien Casetta wrote:

Hi all, 

I am modeling a hot water system with a tempering valve (step 1 : a fraction of the cold flow is sent to the heat source to be heated up, step 2 : the other is mixed with the resulting hot flow). However, in my case, I can't use the built-in component "tempering valve". Indeed, another hot flow is added between step 1 and 2 so the component equations are not valid anymore. Yet, I haven't found any satisfactory method to handle this. Here is what I have tried out : 

- The flow diverter parameter Y (step 1) is set by user-provided equations (equations box), function of temperatures and flow rates in the loop + set temperature

--> convergence problems 

- The flow diverter parameter Y (step 1) is set by a controller (PID or iterative). However, when the set temperature is reached, tracking error tends to 0 and so does the control signal (connected directly to the valve opening Y). It is not the solution at a given time step. Controller output should not be linked direcly to the valve opening (but to its derivative I guess). 

--> stability problems (it oscillated around the set temperature)

Do you have any idea how to solve this simple problem? 

Please let me know if I am not clear enough. 

Thanks in advance,

Regards,

Damien CASETTA

INSA Lyon / Génie Energétique et Environnement

ENERTECH / Cabinet SIDLER

26160 Félines sur Rimandoule

Tél & Fax : 04 75 90 18 54

Courriel : damien.casetta@gmail.com

Site : www.enertech.fr

_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@cae.wisc.edu
https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
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@tess-inc.com

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