[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[EnergyPlus_Support] Re: Exceeded Max Iterations Trouble Shooting
Yeah the problems typically occur when I move to a much more demand control simulation and I can see how it becomes a nasty numerical problem. Even when I am actually doing controls work I know how much of an issue having all those PID loops (although I tend to just use PI loops) I see how hard to tune a system with all those "springs" is so I can imagine how difficult it can be to numerically calculate energy consumption.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Griffith, Brent" <brent.griffith@...> wrote:
>
> 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
>
>
> I hope someone knows the answer, because it's been bothering me every so often, too.
>
> p.s., Great explanation and great effort to research answers before posting! I'm inclined to think that those warnings for specific days are OK, but would like to have more confidence. I'm guessing that they occur at startup of the HVAC system when things are less stable.
>
> James V Dirkes II, PE, BEMP, LEED AP
> www.buildingperformanceteam.com<http://www.buildingperformanceteam.com/>
> Energy Analysis, Commissioning & Training Services
> 1631 Acacia Drive, Grand Rapids, MI 49504 USA
> 616 450 8653
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of ntraughpee
> Sent: Tuesday, October 23, 2012 5:18 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Subject: [EnergyPlus_Support] Exceeded Max Iterations Trouble Shooting
>
>
>
> So this is a problem I seem to have on a regular basis and I am attempting to trouble shoot it.
>
> I do a lot of retrofit modeling and one of the big sources of potential savings we have is from upgrading older pneumatic systems with OA resets (if they even operate) to newer electronic demand control systems. However, one problem I always seem to run into is it saying that the maximum number of iterations have been exceeded (or the average) where E+ has an issue converging the time steps into smooth iterations. That is to say that the difference in values from one iteration to the next is larger than E+'s tolerance which causes E+ to do more iterations until it can "converge" the values.
>
> http://energyplus.helpserve.com/Knowledgebase/Article/View/24/33/maximum-iterations-exceeded
>
> The above article goes over what some of the problems are involving this particular warning but it never explicitly says that this warning means your results are invalid. For instance, in the model I am running now which gives me the exceed max iterations warning, when I view the results in ResultsViewer I see that the issues only occur on specific days during specific time intervals (ie I'll have ~500 errors in one day) but the energy consumption, the HVAC system, and the zone temperatures all appear to be within reason. So if everything looks fine would this model be considered valid or not?
>
> Furthermore, this E+ article explicitly states that E+ has an issue attempting to converge values using the higher order SetpointManager functions which more accurately detail demand control HVAC systems.
>
> Now I have been attempting to increase the amount of time steps per hour which hasn't fixed the error and I have read that you can use the ConvergenceLimits object to fix this but I don't really know how it would be fixed.
>
> If everything looks good in trouble shooting is it something to worry about? Is there a way to up the max iterations, increase the modeling run time and fix the problem?
>
------------------------------------
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/