[TRNSYS-users] Convergence errors with adaptive temperature limits

David BRADLEY d.bradley at tess-inc.com
Mon May 6 07:25:20 PDT 2013


Tom,
   Good job decreasing the time step and making sure that the zone 
capacitance was reasonable!

   Almost all of the controller components in TRNSYS (and in fact 
controllers in real life) have a deadband around the setpoint. In 
cooling mode, if the set point is 21C, the cooling system might not 
start until the temperature reached 21.5C and then it would continue to 
operate until the zone temperature got down to 20.5C (or something like 
that). Controllers (again both in TRNSYS and in the real world) also 
often implement some form of a limit on the number of oscillations that 
they may go through in a period of time. Unfortunately, it is not 
possible to implement either a limit on controller state changes or a 
thermostat dead band using equations. You may be able to implement a 
dead band in Excel but it won't be easy. There is an outside air reset 
controller (which basically does the same as your adaptive temperature 
control) in the TESS Controls Library (Type1250). If you do not have 
that component then I would recommend that you use a Type2 (the instance 
in the Studio that is labeled Aquastat: Cooling Mode: Type2-AquastatC) 
within your equation to provide yourself with a dead band and a limit on 
state-changes.

On 5/6/2013 05:40, Tom B wrote:
> Dear Marcello,
>
> you're absolutely right about this, the formula was unnecessarily 
> complicated. I deleted this variable and the number of convergence 
> errors decreased indeed, but unfortunately did not go away completely.
>
> I also tried looking at it from a different point of view. According 
> to the list file, the convergence errors occur between Type 56 and 
> type 62 (calling Excel) which are part of the loop. Type 62 components 
> outside the loop do not give any problems. Is there something that 
> makes Type 62 inadequate for loops? And if so, could I adjust some 
> value or component order to make sure that I can use Type 62 in a loop?
>
> Kind regards,
>
> Tom
>
> ------------------------------------------------------------------------
> From: marcello.caciolo at cofelyaxima-gdfsuez.com
> To: trnsys-users at cae.wisc.edu
> Date: Mon, 6 May 2013 12:03:57 +0200
> Subject: Re: [TRNSYS-users] Convergence errors with adaptive 
> temperature limits
>
> Dear Tom,
>
> Actually you are right, I misunderstood your question and gave you the 
> same equation you used.
>
> As a second guess, I would say that your problem is in the definition 
> of the variable "cooling need". If I well understand, you compute 
> cooling need by using the actual temperature calculated by type 56 and 
> comparing it to your target temperature. This could be the reason of 
> the bad behavior of your simulation and it is not necessary. Indeed, 
> if your actual temperature is lower (in the case of cooling) of the 
> target temperature, cooling need is zero anyway.
>
> Try to remove this variable and rerun the simulation.
>
> Hope this helps.
>
> Best regards,
>
> *Marcello Caciolo*
> Responsable Outils et Méthodes d'Analyse Energétique
>
> cid:image003.jpg at 01CD4E08.954D04D0
> *
> *Cellule Efficacité Energétique et Environnementale - Pôle Projets et 
> Réalisations
> 46 Boulevard de la Prairie au Duc
> BP 40119 - 44201 Nantes Cedex 02
> Tél.: +33 02 40 41 06 57
> marcello.caciolo at cofelyaxima-gdfsuez.com 
> <mailto:prenom.nom at aximaseitha-gdfsuez.com>
>
> P*Pensez à l'environnement avant d'imprimer ce message*
>
> *De :*trnsys-users-bounces at cae.wisc.edu 
> [mailto:trnsys-users-bounces at cae.wisc.edu] *De la part de* Tom B
> *Envoyé :* lundi 6 mai 2013 11:53
> *À :* TRNSYS users mailing list at the Solar Energy Lab, UW-Madison
> *Objet :* Re: [TRNSYS-users] Convergence errors with adaptive 
> temperature limits
>
> Dear Marcello,
>
> First of all, thank you very much for your response, it is much 
> appreciated. I tried your formula as well, but I'm afraid this is not 
> the problem, because it still gives the same errors. This may be 
> because the formula is in fact the same, just written down differently 
> (because the part between brackets is reversed, the plus turns into a 
> minus). I hope you or someone else may have another suggestion.
>
> Kind regards,
>
> Tom
>
> ------------------------------------------------------------------------
>
> From: marcello.caciolo at cofelyaxima-gdfsuez.com 
> <mailto:marcello.caciolo at cofelyaxima-gdfsuez.com>
> To: trnsys-users at cae.wisc.edu <mailto:trnsys-users at cae.wisc.edu>
> Date: Mon, 6 May 2013 10:50:59 +0200
> Subject: Re: [TRNSYS-users] Convergence errors with adaptive 
> temperature limits
>
> Dear Tom,
>
> I think that your problem is in the definition of the cooling 
> temperature. It should read :
>
> T_Cool_On = 30 - Cooling_need*Cooling_schedule*(30 - Target_temperature)
>
> In this way, cooling temperature is 30 when cooling need and/or 
> cooling schedule are zero, and your target temperature when both 
> cooling need and cooling schedule are 1.
>
> Hope this helps.
>
> Best regards,
>
> *Marcello Caciolo*
> Responsable Outils et Méthodes d'Analyse Energétique
>
> cid:image003.jpg at 01CD4E08.954D04D0
> *
> *Cellule Efficacité Energétique et Environnementale - Pôle Projets et 
> Réalisations
> 46 Boulevard de la Prairie au Duc
> BP 40119 - 44201 Nantes Cedex 02
> Tél.: +33 02 40 41 06 57
> marcello.caciolo at cofelyaxima-gdfsuez.com 
> <mailto:prenom.nom at aximaseitha-gdfsuez.com>
>
> P*Pensez à l'environnement avant d'imprimer ce message*
>
> *De :*trnsys-users-bounces at cae.wisc.edu 
> <mailto:trnsys-users-bounces at cae.wisc.edu> 
> [mailto:trnsys-users-bounces at cae.wisc.edu] *De la part de* Tom B
> *Envoyé :* samedi 4 mai 2013 13:39
> *À :* trnsys-users at cae.wisc.edu <mailto:trnsys-users at cae.wisc.edu>
> *Objet :* [TRNSYS-users] Convergence errors with adaptive temperature 
> limits
>
> Dear all,
>
> In short, I'm facing a problem in which I would like to use a formula 
> for cooling which works perfectly for heating, but gives convergence 
> errors when I apply it to my cooling temperature. It occurs 
> when I'm using adaptive temperature limits in an energy calculation to 
> find the efficiency of a certain shading device. I tried increasing 
> the thermal capacitance to 5*1.2*1.007*roomvolume, the moisture 
> capacitance to 7, I've used time steps varying from 5 minutes to 1 
> hour, but nothing works. Eventually this results in a fatal error, or 
> if I increase the Limits drastically it only slows down my simulation 
> enormously. I'm using Trnsys 17 by the way.
>
> *Problem description*
>
> I've used a 4199.1 kJ/h for both heating and cooling, so given a floor 
> area of 19.44m2 that would be 60W/m2. I've included a file of a 
> project where I isolated this adaptive temperature limit and 
> heating/cooling schedule, so without any shading. One of them shows 
> the situation when there are no convergence errors, but T_Cool_On 
> remains zero degrees, and the other one where in my mind the formula 
> is correct, but convergence errors occur.
>
> I think I found where the problem occurs, but I don't know what I'm 
> doing wrong. I use a loop from type 56 to an equation, in which the 
> acceptable indoor temperature depends on the outside temperature 
> (people tollerate higher temperatures if it's warm outside as well), 
> and is compared to the actual indoor temperature to see whether the 
> cooling/heating should be on or off. This goes to another equation to 
> incorporate the annual occupancy schedule for heating and cooling, 
> which is then lead back to type 56.
>
> *Heating goes fine, cooling becomes a problem*
> Strangely enough, I use similar formulas for heating and cooling, and 
> while heating does not give any problems, the cooling does. This is 
> what I use:
>
> T_Heat_On = Heating_need*Heating_schedule*(Target_temperature - 15) + 
> 15 --> 'need' and 'schedule' give either a 0 or 1, and in this way the 
> heating goes on either when the indoor temperature drops below the 
> target temperature while the building is occupied, or when the 
> temperature drops below 15 degrees at any time.
>
> T_Cool_On = Cooling_need*Cooling_schedule*(Target_temperature - 30) + 
> 30 --> I tried to do the same for cooling, so it would cool when it 
> would become too hot, or when the temperature would rise above 30 
> degrees when the building is unoccupied. Strangely enough, this only 
> works when I leave out the maximum of 30 degrees (so T_Cool_On = 
> Cooling_need*Cooling_schedule*Target_temperature), but if I'm not 
> mistaking, this means that at times when the building is not occupied 
> or no cooling is needed, the T_Cool_On is equal to 0, meaning that the 
> heating and cooling start to compete with each other because the 
> cooling 'wants' a lower temperature than the heating.
>
> Could someone please tell me what might cause this convergence error, 
> and possibly also how to solve this? Thank you very much in advance!
>
> Kind regards, Tom
>
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
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
http://www.trnsys.com

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