[TRNSYS-users] "Advanced" tempering valve

[David BRADLEY]

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 at gmail.com/* 
> <mailto:damien.casetta at gmail.com>
> */Site : /**/www.enertech.fr/* <http://www.enertech.fr/>
>
>
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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
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