[TRNSYS-users] Fan mass balance failed

[David BRADLEY]

Ahmed,
   The fan mass balance probably failed because the input mass flow rate 
to the fan was left unconnected. Type56 does not have an output for the 
mass flow rate of ventilation air to my knowledge so while you can (and 
should) pass the flow rate of air into Type56, you can't pass it through 
Type56 and back to the Type112. In order to avoid that warning, you can 
simple connect the flow rate output of Type121 back to the fan.

   As far as the different results are concerned, there are a couple of 
things to check. First, make sure that they system is actually 
maintaining the set point temperatures in the zone. Type56's HEATING and 
COOLING types are idealized and have infinite capacity. Type92 and 
Type121 have limited capacity and may therefore be limited in the amount 
of energy that they can deliver to the zone. If they aren't delivering 
enough, the zone temperature will fall away from its setpoints. Second, 
make sure that you are looking at outputs of energy transferred to the 
air stream, not energy (or fuel) consumed by Type92 or Type121. Loads 
again are ideal and do not take into account the efficiency (COP, EER, 
etc) of the system that is delivering the energy. Third, Type56 is 
reporting sensible loads only while Type92 (if you are correctly 
accounting for the psychrometrics on the air stream by having a Type33 
on the outlet side of Type92 in case the Type92 set point is below the 
air's wet bulb temperature) may be removing some latent energy as well.

Kind regards,
  David


On 12/28/2011 22:15, ahmed hamdi wrote:
> Hi,
>
> I designed an A/C system consists of Type 112b fan followed by Type 92 
> auxiliary cooler followed by Type 121b heater. I controlled this 
> system using the Type 108 thermostat as mentioned in the Restaurant 
> Example. My problem is that after running the simulation and comparing 
> the loads with the loads i got when i used Type 56 only without any 
> additional fans, coolers, or heaters, i found that the results are 
> completely different.
>
> I noticed a warning stating that the fan mass balance failed during 
> 8760 time steps, which is the duration of my simulation. I am not sure 
> what is the problem, and will appreciate your support.
>
> Thanks,
> Ahmed
>
>
> _______________________________________________
> 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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