[TRNSYS-users] Controller Type2b seems to generate error in flat plate collector outlet temperature

[David BRADLEY]

Hooman,

   I doubt that Type2 is doing the wrong thing. It might be worth 
reading the reference manual section on Type2 if my reply does not make 
sense but my guess is that early in the morning there is enough solar 
energy to heat up the stagnant collector fluid above the Type2 turn on 
temperature difference. However, as soon as the pump starts flowing the 
outlet temperature drops again because there is not enough solar to 
maintain the outlet temperature of flowing liquid above the temperature 
difference. The controller probably oscillates back and forth between 
the possible decisions (pump on vs pump off) and cannot converge so it 
"sticks." In your case it sticks in the pump-off position so you see a 
bit temperature spike until there is enough solar radiation to maintain 
the outlet temperature above the turn-on temperature difference.

   If you are using Type1 then it is important to be aware that this 
collector model ignores the thermal capacitance of the collector 
materials themselves as well as that of the fluid contained in the 
collector. As a result the collector reacts to changes very fast 
(sometimes unrealistically fast). You could use Type539 from the TESS 
Solar library if you have access to it. That collector model accounts 
for the capacitance of the collector itself. Also make sure that you are 
using a reasonably short timestep (1-5 minutes) and that there is not 
some unrealistic mismatch between the size of the tank, the area of the 
collector array and the flow rate of the pump.

kind regards,

  David



On 09/15/2018 04:48, Hooman Azad via TRNSYS-users wrote:
>
> Dear friends
>
> Please check my simple circuit. A 150 kg tank is supposed to be 
> maintained at 60 degrees all year. A flat plate collector has been 
> employed. When you run the simulation (file FPC1), you see some sharp 
> rises of collector outlet temperature, as high as 400 degrees, which 
> are obviously wrong.
>
> If you remove the type2b controller and, for example, control the pump 
> with type14h (file FPC2), the sharp rises disappear. It seems type2b 
> is responsible for the errors in the first case. Thank you very much 
> for your kind help.
>
> Hooman
>
>
>
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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
http://www.trnsys.com

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