[TRNSYS-users] Equation's problem

[David Bradley]

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 at engr.wisc.edu
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