[TRNSYS-users] Auxiliary Heater and Stratified Storage Tank

[Haluf, Christopher]

Dear TRNSYS-Users,

I'm modelling an easy system that consists of a pump (Type 3b), an auxiliary heater (Type 6) and a stratified storage tank (Type 4a). I've attached my .tpf-file, so you can comprehend what I'm writing.



I'm doing this simulation because I want to get familiar with the behavior of a tank while it is loaded. I set the losses of each component to 0 and the efficiencies to 1, so that I have a loss-free system.

Concerning the heater, I set the "maximum heating rate" to 10 kW and the "set point temperature" to 100°C. I defined 3 nodes besides the top and the bottom in the tank, so I have 5 nodes. I set the "initial temperature" for each node to 20°C. The volume of the tank is 1m³ and I disabled the internal heaters, so that all of the heat is provided by Type6.

What I want to do, is to check if all of the energy which is provided by the Heater gets into the tank. Therefore, I run the simulation for 10 hours. Now, I calculate the energy provided by the heater which is 10 kW * 36.000 s = 360.000 kJ. In order to control if all of this energy got into the tank, I take the highest and the lowest value of the average tank temperature which is the delta T. Cp for water is 4.19 kJ/kg*K and the mass of the water is 1.000kg. Now, I can calculate the internal energy of the tank (1000 kg * 4.19 kJ/kg*K * (74.2°C-20°C) = 227.098 kJ). This value is definitely much lower than the energy that is provided by the heater...

Another strange thing is, that the average tank temperature begins with a value of 0°C. I don't understand this, because I set the initial temperature for all nodes to 20°C, so I think that the average tank temperature should have the same value...

Could someone of you please have a look at my simulation and see if there is something wrong. And if there is all right, could you please explain the bahvior of the tank? It would be very helpfull for me!

Thank you in advance!


Mit freundlichen Grüßen / Kind regards
Christopher Haluf
Intern

Siemens AG
Corporate Technology
CT PS 3
Günther-Scharowsky-Str. 1
91058 Erlangen, Deutschland
Tel.: +49 (9131) 7-24724
Fax: +49 (9131) 7-21339
mailto:christopher.haluf at siemens.com

Siemens Aktiengesellschaft: Vorsitzender des Aufsichtsrats: Gerhard Cromme; Vorstand: Peter Löscher, Vorsitzender; Wolfgang Dehen, Heinrich Hiesinger, Joe Kaeser, Barbara Kux, Hermann Requardt, Siegfried Russwurm, Peter Y. Solmssen; Sitz der Gesellschaft: Berlin und München, Deutschland; Registergericht: Berlin Charlottenburg, HRB 12300, München, HRB 6684; WEEE-Reg.-Nr. DE 23691322


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