Re: [EnergyPlus_Support] iterations for fan-coils and warnings

Francisco,

Although I don't have many details of your model, a few things come to mind which may be helpful:

Variable air and water flow rates is probably a more difficult situation to converge than only one flow rate.Â I think convergence is expressed in degrees C. If so, 0.001C is very tight and could be relaxed.
You might consider reviewing the output to see when this convergence problem occurs. If it is at the start of an occupancy period, for example, that is probably normal because of the sudden change of setpoint. Your review may indicate some other condition that would make convergence more difficult (and thus more explainable)
LEED reviewers are normally very competent people, but have much less familiarity with your model than you do. They are not necessarily familiar with your software, either. All that you can do to convey that you have "done your homework" by carefully reviewing inputs and output will help them believe your results.

On Fri, Dec 30, 2016 at 11:35 AM, fpasserini.tn@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Â

Hello,
the LEED reviewers have asked the reason of many warnings.
Many are of the following kind:
Â
Â Â *************Â ** Warning ** ZoneHVAC:FourPipeFanCoil="0AZ1:CUCINA FAN COIL UNIT"Â -- Exceeded max iterations error (sensible runtime) continues...
Â Â *************Â **Â Â ~~~Â Â **Â Â This error occurred 5842 total times;
Â Â *************Â **Â Â ~~~Â Â **Â Â during Warmup 114 times;
Â Â *************Â **Â Â ~~~Â Â **Â Â during Sizing 0 times.
Â
In the .err file there is also:
Â
** Warning ** ZoneHVAC:FourPipeFanCoil="0AZ1:CUCINA FAN COIL UNIT" -- Exceeded max iterations while adjusting cycling fan sensible runtime to meet the zone load within the cooling convergence tolerance.
Â Â **Â Â ~~~Â Â ** Iterations=100 During Warmup, Environment=MILANO-LINATE ANN CLG 1% CONDNS DB=>MWB, at Simulation time=07/21 22:15 - 22:30
Â
The control method of the fan-coil units is VariableFanVariableFlow
Both the â??Cooling Convergence Toleranceâ?? and the â??Heating Convergence Toleranceâ?? are equal to 0.001.
In the object ConvergenceLimits the â??Maximum HVAC Iterationsâ?? are equal to 25.
What do you suggest? Should I change some parameters or should I explain the reason to the reviers?

Best Regards and happy new year!

James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
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Website l Â LinkedInÂ | May 2016 ASHRAE Journal article on energy modeling

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