[TRNSYS-users] Convergence errors with adaptive temperature limits

[marcello.caciolo at cofelyaxima-gdfsuez.com]

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
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De : 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
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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