Re: [TRNSYS-users] Equation's problem

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

Samuele,
  I am not quite sure what you are trying to model. The loop that
contains Type654-2, Type700, Type650, and Type60 is not converging. The
pump is ON from 06h00 to 18h00. The liquid gets hot going through the
boiler then goes into a heat exchanger whose hot side flow rate is
modulated in order for the cold side outlet temperature not to
come out any hotter than the temperature profile set by Type14e. Water
comes into the heat exchanger at 0C with a flow rate of 8000 kg/h. The
set point temperature function becomes 0 at 15h00 but the pump is still
running on the hot side so the heat exchanger is trying to maintain a 0C
temperature rise across the cold side between 15h00 and 18h00.

  The other pump is ON if it is between 18h30 and 0h00 and the
temperature of the tank is greater than 44C. Using equations as control
signals can be a little dangerous because you lose the ability to model
hysteresis in the controller. The pump would turn on at a tank
temperature of 44.0000000000000001 and off again at a temperature of
44.0000000000000000. I would recommend using a controller model such as
Type2 or Type503 (cooling aquastat in the TESS controllers library)
because those models have deadbands that can avoid the convergence
problems of equations.
Cheers,
 David



At 04:51 6/6/2007, Samuele wrote:
>    
> Dear all,
>  
>     I have done a simple project (enclosed)
> in which there are a pump, a boiler, an heat exchanger, a thermal storage
> and another pump controlled by an equation.
>  
>     I think there are no errors but, if I
> changed some values ( for example the temperature's value in type 14e-2
> or the value for the gt equation which controlls the function of the
> pump)
>     It doesn't run.
>  
>     Could anybody tell me if the problem is
> the equation which calculates the control function of the pump?
>  
>     Best regards,
>                           
> Samuele.
>     
>
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> TRNSYS-users@engr.wisc.edu
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