[TRNSYS-users] Calculating right mass flow and outlet temperature for programmed boiler

[Böttner, Jan]

Hi,

I have been programming a log gasification boiler based on its behavior in reality. Unfortunately I have trouble calculating the right mass flow and the outlet temperature.
In praxis, the mass flow changes and is variable. But the same goes for the outlet temperature. It increases with time. Since they are dependent on each other (Q = m*cp*deltaT -> m = Q/(cp*deltaT)) I can't figure out how to correctly calculate m and T_out.
A little about the boiler and system:
It has a nominated power and a part load ratio and switches off, when the outlet fluid temperature reaches a certain point. So you could say, the amount of energy transferred to the fluid per time is fixed. The boiler is connected to a storage tank and the fluid entering the boiler (coming from storage tank) is tempered with the outgoing fluid so that T_in has a minimal temperature of 65°C.

I now have two unknowns, m and T_out (and three know, Q, cp and T_in). Since in praxis they both vary, I can't say that one is fixed, at least not completely. I tried setting some boundaries with a minimal and maximal mass flow but I couldn't figure it out.

Is there a way, type or solution of any kind, where TRNSYS calculates an optimal mass flow/outlet temperature for the system?
I feel like I'm forgetting about or missing something essential to all of this.
Thanks a lot for any help!

Best regards, Jan
(if needed I can provide the F90 file for the boiler, it's jus not very clean and I don't know if it really helps)

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