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RE: [EnergyPlus_Support] Exceeded Max Iterations Trouble Shooting
Version 7.2 was changed to revamp the information reported in such warning messages (if you use Output:Diagnostics, DisplayExtraWarnings ).
It can now detect some types of numerical oscillation that show which part of the solution is not converging and causing it to keep on iterating up to the maximum limit. If the messages indicate it found oscillations then there is probably nothing to be done to fix it but you can narrow down which device is the one not finding a unique solution. If the magnitude of the oscillations seem reasonable then the results can be trusted.
It can also now detect if some results are changing monotonically over iterations. If the messages indicate monotonic changes have been found it is probably worthwhile to try to address the issue by raising the limit which can be set in the ConvergenceLimits object input field called Maximum HVAC Iterations.
One main cause for these that I know of occurs when VAV air terminal units are just lifting off the minimum stop and air side economizer cooling is available. The fluctuations in damper position, return air temperatures, OA fraction, and mixed supply air temperature form a nasty numerical problem. You can test without economizer on to see if it clears up. This is a known issue and there doesn?t seem to be anyway to fix the problem on input, but the results should be okay.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jim Dirkes
Sent: Tuesday, October 23, 2012 6:50 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Exceeded Max Iterations Trouble Shooting
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