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Re: [TRNSYS-users] Cooling loads... Strange results (energy balance)

Thibault,
Are you using the Type56 summary files for your energy balance? I have had terrible problems trying to construct energy balances out of individual NTYPES. The balances are much more complete - the problem with them is that you can't rely on them if you are running a timestep less than 1 hour because if you are using a smaller timestep, they don't integrate over the hour - in that case, they just give you the energy balance for the last timestep of the hour. 
Kind regards,
David


Thibaut VITTE wrote:

David,

Thanks for your help.
I checked my schedules, and there is nothing specially correlated with the pikes. As I said, the pikes can appear on different days, "depending" on minor changes in the simulation, and happen on different hours as well. This is not a convergence problem in the TRNSYS solver, but i checked the energy balance, and I do have problems with that. The energy balance is totally wrong (up to 2.15*10^6 kJ/hr) on these timesteps, and the Qtrans value goes from negative (which is normal, due to solar radiations) to positive (more than the opposite) in one time step. It can be seen on the surfaces' temperature that goes down for the timesteps where the loads are meaningless.
I think my problem comes from great coupling air flows (up to one third of a volume in one hour, I have virtual walls). Am I right ? Is there a way to avoid this, is there a parameter to tune to make the energy balances more precise ? 

Thanks in advance.


David Bradley a écrit :

Thibault,
Is it possible that there is a change in zone set point at those times? Technically, there is an infinite load on the space when the space temperature is changed by returning from a setback or setup temperature. You should be able to tell if there is a convergence problem by looking at the *.lst file - it will let you know whenever the system didn't converge. 
Kind regards,
 David


Thibaut VITTE wrote:

Dear Trnsys Users,
I'm working on a rather big building, and I have a strange behaviour, that I don't understand. The cooling loads computed by Trnsys follow a normal pattern, except some days, for one or 2 points that ar 3 to 4 times greater than the baseline. 
I've attached a picture to explain it better.
I've thought it was a bug in my inputs, so I tried to disable solar radiations, temperature, internal gains, I double checked my schedules, I... and I found nothing. Actually I found some minor errors, and they had an effect on the pattern (for example the "pikes" appear later in the year), but the behaviour is still erratic.
So, is it possible that a convergence problem (even though I have a 10^-3 tolerance convergence) makes this erratic behaviour ? It is a big building, with shading masks, internal windows, high coupling air flows (exactly in the zones that show the unexplainable loads), and the simulation takes a pretty long time. 

I Hope someone has some answer, because I really don't see!..

Thanks in advance
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Thermal Energy System Specialists (TESS), LLC David BRADLEY 22 N. Carroll Street - Suite 370 Partner Madison, WI 53703 USA 
P: +1.608.274.2577 F: +1.608.278.1475
E-mail: bradley@tess-inc.com Web Pages: http://www.tess-inc.com and http://www.trnsys.com 

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--
***********************************************************************
Thermal Energy System Specialists (TESS), LLC David BRADLEY 22 N. Carroll Street - Suite 370 Partner Madison, WI 53703 USA P: +1.608.274.2577 F: +1.608.278.1475 E-mail: bradley@tess-inc.com Web Pages: http://www.tess-inc.com and http://www.trnsys.com 

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