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Re: [TRNSYS-users] TRNSYS Message 441 with Type 56 and Type 921
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
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--
***************************
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@tess-inc.com
http://www.tess-inc.com
http://www.trnsys.com