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

[David Bradley]

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
>>>
>>> ------------------------------------------------------------------------ 
>>>
>>>
>>>
>>> ------------------------------------------------------------------------ 
>>>
>>>
>>> _______________________________________________
>>> TRNSYS-users mailing list
>>> TRNSYS-users at cae.wisc.edu
>>> https://www-old.cae.wisc.edu/mailman/listinfo/trnsys-users
>>>   
>>
>> -- 
>> ***********************************************************************
>> 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 at tess-inc.com Web Pages:  http://www.tess-inc.com    
>> and      http://www.trnsys.com
>>
>> ***********************************************************************
>
>

-- 
***********************************************************************
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 at tess-inc.com 
Web Pages:  http://www.tess-inc.com    and      http://www.trnsys.com

***********************************************************************