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# EnergyPlus SimHVAC errors and iterations warnings

I am modeling infiltration studies in one block....I encountered in following problem, How to resolve this error

Warning ** SimHVAC: Maximum iterations (20) exceeded for all HVAC loops, at AXON CFD ANALYSIS (01-01:31-12), 01/02 05:00 - 06:00
**   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
**   ~~~   ** ...use Output:Diagnostics,DisplayExtraWarnings; to show more details on each max iteration exceeded.
** Warning ** SimHVAC: Maximum iterations (20) exceeded for all HVAC loops, at AXON CFD ANALYSIS (01-01:31-12), 01/02 05:00 - 05:03
**   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
** Severe  ** PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0 [-1.42805].
**   ~~~   ** pb =[-126410.14], tdb=[30.32], w=[1.0157873E-002].
**   ~~~   **  Routine=Unknown, Environment=AXON CFD ANALYSIS (01-01:31-12), at Simulation time=01/02 05:00 - 05:03
**  Fatal  ** Program terminates due to preceding condition.
...Summary of Errors that led to program termination:
..... Reference severe error count=1


Here is the IDF file in question.

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Please don't tag people directly (with the "@"). Tag your question correctly instead (eg: you are clearly missing "energyplus" as a tag) and it'll get to the right people's eyes.

( 2018-05-16 02:51:53 -0600 )edit

@Julien Marrec........I have been doing that.....but there is no response for most of my queries....when I had seen other people queries ....they are getting answers from experts....I was like why are they not looking at my post? that is why with that intention I made one of the guy in the loop...sorry for that....

( 2018-05-16 07:18:11 -0600 )edit

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These max iteration warnings are very hard to diagnose. You have a very simple air loop defined. I see that you are using air flow network and I suspect this is the root of the warnings. I disabled air flow network by changing the AirflowNetwork:SimulationControl input for AirflowNetwork control to NoMultizoneOrDistribution and the max iteration warnings are gone.

************* EnergyPlus Completed Successfully-- 15 Warning; 0 Severe Errors; Elapsed Time=00hr 00min  4.47sec


Changing the control input back to MultizoneWithDistribution causes the max iteration warnings.

** Warning ** SimHVAC: Maximum iterations (20) exceeded for all HVAC loops, at AXON CFD ANALYSIS (01-01:31-12), 01/02 05:00 - 06:00
**   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
**   ~~~   ** ...use Output:Diagnostics,DisplayExtraWarnings; to show more details on each max iteration exceeded.
** Warning ** SimHVAC: Maximum iterations (20) exceeded for all HVAC loops, at AXON CFD ANALYSIS (01-01:31-12), 01/02 05:00 - 05:05
**   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
** Severe  ** PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0 [-1.61928].
**   ~~~   ** pb =[-130808.27], tdb=[7.42], w=[1.9966870E-003].

************* EnergyPlus Terminated--Fatal Error Detected. 15 Warning; 1 Severe Errors; Elapsed Time=00hr 00min  3.12sec


I suggest adding more Output:Variable reports to show how the simulation is proceeding up to the point where the fatal occurs to see if you can identify anything wrong with your inputs. Your goal is to find reasons for the severe error:

** Severe  ** PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0 [-1.61928].
**   ~~~   ** pb =[-130808.27], tdb=[7.42], w=[1.9966870E-003].
**   ~~~   **  Routine=Unknown, Environment=AXON CFD ANALYSIS (01-01:31-12), at Simulation time=01/02 05:00 - 05:05


If you cannot find a reason for this issue then I suggest posting your question and input file on the HelpDesk and note that you are using AirFlowNetwork so that the AFN expert can respond. See http://energyplus.helpserve.com or send a message to energyplus-support@gard.com.

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The AirflowNetwork expert responded on the HelpDesk and noted that only 1 fan was allowed in the air loop. The IDF above shows use of a return and supply fan. Removing the return fan allowed the simulation to proceed to completion without max iteration warnings.

( 2018-05-18 08:03:10 -0600 )edit

( 2018-05-18 10:34:06 -0600 )edit