[TRNSYS-users] Tank Type 534

[Jeff Thornton]

Andrea,

The stored energy output of Type 534 gives the rate of change of energy of the fluid within the storage tank.  If the tank as a whole is getting hotter than this value will be a positive number.

When you integrate volume x density x specific heat as you did you are missing the temperature component of the energy.  A great way to check is with the units.  Volume x density x specific heat gives units of kJ/K.  When you integrate this you get kJ.h/K; very different from the units of kJ/h that the TRNSYS output is calculating.

If you want to check the output from 534, the correct calculation would be:

Storage Rate = Volume x Density x Specific Heat x (Tfinal - Tinitial) / Timestep

Jeff / TESS

Sent from my iPhone

> On Jan 22, 2019, at 6:44 AM, Andrea Diaz Guasgua via TRNSYS-users <trnsys-users at lists.onebuilding.org> wrote:
> 
> Dear group,
> 
> 
> I am trying to understand the energy balance from the following scheme. A boiler(Type 751) sends its temperature and flow to port 1 of a storage tank (Type 534 with two nodes and ports). I left port 2 disconnected with its temperature set to a constant value equal to the boiler's output temperature and flow equal to zero. 
> 
> 
> From my understanding I am injecting energy from the boiler into the tank only. So I computed the tank stored energy as Store_Energy_Tank = Volume_Tank*SpecificHeatCapacity*density, and then integrated over 1 hour period so I can get the rate. I thought this calculation should be approximately to the output from the tank called "Tank Energy Storage Rate [KJ/hr]", but apparently is not. Also, I checked some examples from TRNSYS library and this value is negative. 
> 
> 
> My questions are how can I compute the stored energy in a tank and what do the signs means?
> 
> 
> I would appreciate your help,
> 
> 
> Regards,
> 
> Andrea 
> 
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