[TRNSYS-users] Wet cooling tower modeling

[David BRADLEY]

Mohamed,
   Chun Kwon is correct in his comments. I thought I would just add some 
other things that I noticed.

1. As Chun Kwon mentioned, you need to add some thermal capacitance 
(probably in the form of a tank) in the cooling water loop. You also 
need to reduce your timestep to something on the order of 5 minutes. 
Make sure that all of the storage tanks in the simulation can hold at 
least 1 timestep of fluid in them. The two tanks in your simulation are 
rather small (1m3 and 0.3m3) given the flow rates on your chiller.
2. You have used the same flow rate equation to set all three flow rates 
on the absorption chiller (hot water, cooling water, and chilled water). 
All of the machines that I have seen have a certain ratio of these flow 
rates. I have never seen a machine where all three rated flow rates were 
the same. This might be skewing the performance of the chiller.
3. The thermal capacitance of your building zones is left at the default 
value of 1.2*ZoneVolume, which accounts only for the thermal capacitance 
of the air in the zone, not for any of the furnishings. A better value 
would be approximately 1.2*5*ZoneVolume
4. The chiller's capacity is left at its default value of 1500kW which 
seems rather high, especially given the size of the cooling coil.
5. You correctly caught that you have to set the number of Type4 tank 
nodes on both the parameters and the outputs tab of the Type4 proforma. 
However, be careful, the question that you have to answer is slightly 
different. In one case it asks how many nodes there are and in the other 
case it asks how many nodes there are in addition to the top and bottom 
nodes.

   What is specifically going on in your simulation is that the long 
time step, the lack of capacitance in the cooling loop, and the very 
large chiller capacity are causing one of the flow streams to not only 
freeze but to drop well below -273C at which point the psychrometrics 
routine generates an error.
Kind regards,
  David



On 9/10/2013 07:38, Mohamed Adel wrote:
> Dear All,
> While modeling a wet cooling tower in a simulation i always receive an 
> error from the utility routine psycho-metrics.  Please advise how to 
> fix this error.
> Kindly find attached the needed data.
> Best Regards
>
> Mohamed Adel
> M.Sc. Ing.
>
> SL-Rasch GmbH
> Special & Lightweight Structures
> Kesslerweg 22
> D-70771 Leinfelden-Oberaichen
> t: 0049 176-32315274
> mail:mohamed.adel at Sl-rasch.de
> Best Regards
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
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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