[TRNSYS-users] Tank - energy balance

[Jeff Thornton]

Amaia, 

With small timesteps and tight tolerances, your energy balance should be
nearly perfect. Take into account the change in stored energy and your
balances should be well within 1%. Taker some time and make sure that
they are. If not, it's possible you're noty accounting for a term, have
mismatched fluid properties or even a bad connection. 

As for your second question <In winter there are some peak demands from
the chiller where the tank is enough to absorb the heat from the
condenser, then, how is this translated in the results?>. I'm not sure
what you mean. If the tank can absorb the heat, and does, then the tank
gets hot. You could use this energy for something (meet a heating load,
pre-heat DHW etc), let it decay to the environment through tank losses,
etc. If you're asking how it's accounted in the energy balance, then
we'd have to see the boundaries of your balance to answer that question.


Jeff 

---
Jeff Thornton
President - TESS LLC
3 N. Pinckney Street, Suite 202, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 10/08/2018 12:45 pm, Amaia Zuazua Ros via TRNSYS-users wrote: 

> Hi, 
> 
> Thank you all. I had the timestep for one hour, I have reduced it to 0.1 hour and now the difference between the energy to the load and energy to the source has been reduced considerably (taking one month, earlier the difference was 1.24 MWh and now is 0.2 MWh). Yet, I have a question, I am simulating an office building, where the cooling demand is specially high in summer season but still there is some demand during winter. In winter there are some peak demands from the chiller where the tank is enough to absorb the heat from the condenser, then, how is this translated in the results? 
> 
> Best regards, 
> Amaia 
> 
> El lun., 8 oct. 2018 a las 17:18, David BRADLEY (<d.bradley at tess-inc.com>) escribió: 
> 
> Amaia, 
> 
> There could be two things I think. First, you're right that you need to take into account the change in energy stored in the tank. Type4 has an output that you can use. Second, make sure you are using a small timestep (maybe 5 minutes). With large timesteps you often get problems with energy balances. 
> 
> kind regards, 
> 
> David 
> 
> On 10/07/2018 13:57, Amaia Zuazua Ros via TRNSYS-users wrote: 
> 
> Hi TRNsys users, 
> 
> I am simulating a water to water chiller coupled to two storage tanks one each side of the chiller. It's the first time that I work with tanks (I'm using type 4), and I understand that the energy balance should be accomplish, I mean, the total energy coming from the source should be the same than the energy going to the load, but this is not happening in my case with the condenser side of the chiller (the annual totals have around 10% difference) and still the system seems to work (the idea is to simulate a radiative system that dissipates the heat from the condenser). I don't know if it can be related to the internal energy change of the tank. Could some one give a bit further explanation/information about this? 
> 
> Thanks in advance! 
> 
> Amaia 
> 
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> 
> -- 
> ***************************
> David BRADLEY
> Principal
> Thermal Energy Systems Specialists, LLC
> 3 North Pinckney Street - suite 202
> Madison, WI 53703 USA
> 
> P:+1.608.274.2577
> F:+1.608.278.1475
> d.bradley at tess-inc.com
> 
> http://www.tess-inc.com [2]
> http://www.trnsys.com [3]

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