[TRNSYS-users] TRNSYS Message 441 with Type 56 and Type 921

[David BRADLEY]

Nils,
There are a few things to check:

1) make sure you have a realistic amount of thermal capacitance in your 
zone. The default thermal capacitance is 1.2*1.007*zoneVolume. This 
accounts only for the thermal capacitance of the air in the zone. A more 
realistic value would be 5*1.2*1.007*zoneVolume. This allows for the 
thermal capacitance of the furnishings in the zone as well. Thermal 
capacitance slows down the zone's response to changes in the ambient 
conditions (whether this is ventilation, solar, internal gains, ambient 
temperature, etc).
2) make sure you have a realistic amount of moisture capacitance in your 
zone. The default again only accounts for the moisture capacitance of 
the air in the zone. Use the "humidity" button in TRNBuild to increase 
this value to 7 or 10 in order to account for the moisture capacitance 
of the furnishings in the zone.
3) make sure that you are using a thermostat model (like Type108) and 
not an equation in order to control your air conditioner. Controller 
models have hysteresis like in real controllers so that the equipment 
does not short-cycle.
4) make sure that you are using an appropriate time step. TRNSYS can 
make one control decision per time step. If you decide to turn on an air 
conditioner and leave it on for an hour (ie you are using an hour time 
step) then its going to get very cold in the zone by the end of the 
hour. TRNSYS will then decide that it wasn't such a good idea to have 
turned the air conditioner on for that time step and will iterate, 
trying to find a solution with the air conditioner off. In this case, of 
course, it will be really hot at the end of the timestep so it will try 
again with the air conditioner on. The iterative cycle will continue at 
the same time step and it will never get a converged solution when the 
zone and the thermostat are both in agreement. A 1 or 5 minute time step 
is appropriate.
5) make sure that you are passing the airflow of your VENTILATION into 
Type56 as a mass flow rate and that Type56 is expecting a mass flow 
rate. If you are using TRNSYS 16, you need to pass in an air change 
rate, not a mass flow rate.
Best,
David


On 11/7/2011 15:35, Nils Nikolai wrote:
> Dear All,
>
> I am trying to connect a Type 921 Air Condition unit with the 
> ventilation slot of a Type 56 House and I get the following error 
> message even though Type 921 is not directly connected to Type 56. 
> These two units are connected via an equation unit to split the 
> airflow for the different zone and to mix the air stream with some 
> other devices:
>
> Warning at time : 3281.000000
> Generated by Unit : Not applicable or not available
> Generated by Type : Not applicable or not available
> TRNSYS Message 441 : The inputs to the listed units have not converged 
> at this timestep. The values at the last iteration will be used and 
> the simulation will proceed.
> Reported information : UNITS: 45 56
>
>
> The simulation stops due to the maximum amount of warnings allowed per 
> simulation (Message 450).
>
> I tried to exchange Type 921 with some other air condition units like 
> Type 651 but the error stays the same.
>
> When i narrow the problem down, the error doesn't occur anymore when I 
> disconnect one airflow to one specific zone. How could that be?
>
> Thank you for your help,
>
> Nils Nikolai
> _______________________________________________
> 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