Yes, that sounds correct. That is exactly
the sort of analysis and judgment I’d recommend.
If you are reporting at the “timestep”
frequency, then it is expected that the number of iterations can be larger than
the specified maximum. EnergyPlus has two different modeling timesteps,
zone and system. HVACManage Iterations report variable and the Maximum
Iterations setting are at the system timestep level. If you are reporting
HVACManage Iterations at the timestep frequency, then that is the zone timestep
and the reported value is the sum of all the system iterations for all the
system timesteps within that zone timestep. Report out at “detailed”
frequency if you really need to see the results at the system timestep level.
The tolerance flags and such are not necessarily
intended for users, they are for developers and haven’t been documented
for use by users. But those error messages are saying the problem is in resolving
plant mass flow rates.
From:
Sent: Friday, July 25, 2008 4:08
PM
To:
Subject: [EnergyPlus_Support] Re:
** Warning ** SimHVAC: Maximum iterations (40) exceeded
A little more detail....
A closer inspection of the "HVACManage Iterations" report Variable
reveals big numbers (which are greater than my specified maximum
iterations) almost exclusively at times when a) the system is starting
up because of the Night Cycle manager or b) it's starting up for the
normal occupied period schedule.
Since my various setpoints are met at the same timesteps where the max
iterations are exceeded, it seems that the warning may not indicate any
problem at all for this particular case. Does that sound correct?
p.s., Those Flow tolerance questions on my previous post are still of
interest. I want to have as "clean" a run as possible; that is
greatly
aided by better understanding of all the warnings!
p.p.s., Those Report Variable suggestions, assuming that I've understood
them correctly, are priceless. Thanks!
--- In EnergyPlus_Support@
wrote:
>
> Dear Brent, Richard and others,
>
> I've taken a look at these Report Variables, and I'm not quite sure
what
> some of the information means.
>
> An example is:
>
> ** ~~~ ** HVAC Tolerance Flags=[0000000]
>
Enthalpy[0],
\
> [0]..0=ok,1=
> ** ~~~ ** HVAC Tolerance Values, Most Recent listed first
> ** ~~~ ** HVAC EnthalpyTol=
> HumRatTol=0.
> ** ~~~ ** FlowQualTol=
>
> This appears that everything is OK for the HVAC tolerance issues,
since
> all the values are zero. I don't know what these flags represent,
> though. Do you?
>
> For the PlantFlow Tolerance flags, I appear to have problems:
>
>
> ** ~~~ ** Plant Tolerance Flags=[01000101]
>
Enthalpy[0],
\
> [0],PlantFlowMassFl
>
> ** ~~~ ** Plant Tolerance Values, Most Recent listed first
>
> ** ~~~ ** Plant EnthalpyTol=
> HumRatTol=0.
>
> ** ~~~ ** FlowQualTol=
> TempTol=0.00
> .........
>
>
>
> ** ~~~ ** PlantFlowFlowTol=
>
>
>
>
> I've searched my Report Variable values, which include total air and
> water flows, but these highlighted values do not show up anywhere. So
> once again, I'm not sure what they are.
>
> It would help to know what flow is referred to: Airflow or water
flow?
> Same question for mass, although I suspect that solving a flow problem
> will also resolve the mass problem.
>
> I suspect, too, that "PlantFlow" always refers to a Plant Loop.
In my
> case, that's a hot water heating loop.
>
> In summary:
> 1) If I fail an HVAC tolerance flag, where do I look for a cause? or
> what should I report more extensively to see what's going on?
> 2) If I fail a Plant Tolerance flag, where do I look for a cause?
> 3) Are the flows referred to in the tolerance flags airflow or
> waterflow?
>
> Thanks!
>
>
>
>
> --- In EnergyPlus_Support@
> brent_griffith@ wrote:
> >
> > System iterations are also a report variable. I recommend exploring
> > when the issues occur by looking at the number of iterations
reported
> at
> > the timestep or detailed frequency. See the RDD file of course, but
> the
> > variables are 'HVACManage Iterations' and 'SimAir Iterations'
> >
> >
> >
> > ____________
> >
> > From: EnergyPlus_Support@
> > [mailto:EnergyPlus_Support@
II
> > Sent: Wednesday, July 23, 2008 6:27 PM
> > To: EnergyPlus_Support@
> > Subject: [EnergyPlus_
> > iterations (40) exceeded
> >
> >
> >
> > Dear Brent,
> >
> > That's helpful!
> > I think I'm in the "when things are changing quickly"
situation, but
> > there are a
> > almost every morning in my case. When there are more than a dozen or
> > so of these max iteration conditions, E+ just condenses the rest of
> > them into a message saying that you had "XX" max iteration
warnings.
> > This, of course, means that you don't really know where they're all
> > coming from. My hope is that the first few are representative; if
> > not, I'll be forced to guess a lot.
> >
> > I was hoping to figure out a process that helped identify the source
> > of most of the iteration errors. In my current model, there are
> > relatively few unmet load hours, which I take as a good sign.
> > Nonetheless, there are 2800 maximum iteration warnings and that
seems
> > like a lot...
> >
> > Any other hints?
> >
> > --- In EnergyPlus_Support@
> > <mailto:EnergyPlus_
> > brent_griffith@ wrote:
> > >
> > > Good question, difficult to answer. Here are my 2 cents,
> > >
> > >
> > >
> > > It is something to be concerned about, but in many cases there
does
> > not
> > > seem to be a way to completely eliminate them and they aren't
> > > necessarily a cause for alarm.
> > >
> > >
> > >
> > >
> > >
> > > 1. The total count is a difficult measure to use because it
varies
> > > with number of zones, number and type of air systems, and length
of
> > run
> > > period. A 1,000 might not be a problem for a big model with an
> annual
> > > run, but it could be way too many for a single zone design day
run.
> > The
> > > errors are more common with VAV than CV. The frequency is key
> though.
> > I
> > > look at the timing of the errors. If they happen every time step
> > during
> > > some period, then it usually means there is something wrong with
> HVAC.
> > > If they happen only sometimes, and those times are when things
are
> > > changing quickly (like recovery from setback), then I don't
worry
> > much.
> > >
> > > 2. I depends if the system is succeeding at controlling the zone
> > > conditions. If the systems are controlling well, and the errors
are
> > > intermittent, then the results are probably not affected
> > significantly.
> > > If the systems are not controlling zone conditions, then the
errors
> > are
> > > probably very significant. Check the comfort conditions and zone
air
> > > temperatures to see.
> > > 3. When the errors are significant, they usually indicate
something
> > > is wrong with HVAC input that EnergyPlus isn't able to trap in
some
> > > other way. Possibilities include all sorts of things that can go
> wrong
> > > such as: systems connected wrong (node connections usually),
sized
> > > wrong (mixing hard and auto sizes), controlled wrong (check
> operation
> > of
> > > set point managers by reporting node set point values).
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ____________
> > >
> > > From: EnergyPlus_Support@
> > <mailto:EnergyPlus_
> > > [mailto:EnergyPlus_Support@
> > <mailto:EnergyPlus_
Dirkes
> > II
> > > Sent: Wednesday, July 23, 2008 1:45 PM
> > > To: EnergyPlus_Support@
> > <mailto:EnergyPlus_
> > > Subject: [EnergyPlus_
> > iterations
> > > (40) exceeded
> > >
> > >
> > >
> > > Dear Forum,
> > >
> > > I am wondering whether this warning ("Maximum iterations
....
> exceeded)
> > > is something to be concerned about.
> > >
> > > I get the warning often in varying quantities. Most of my E+ use
is
> > > for LEED projects and I don't want to look (too) silly by
submitting
> a
> > > project to USGBC with a lot of these warnings without
understanding
> it
> > > better.
> > >
> > > 1) If it is a concern, at what frequency? (e.g., "whenever
it
occurs
> > > more than 100? 500? 1000? times in a full year run.")
> > > 2) Roughly how much does it affect accuracy of the simulation?
(A
> lot
> > > or a little? proportional to the number of occurrences?
> > > 3) Any tips about how to avoid it?
> > >
> > > Thanks!
> > >
> >
>
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 not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
__,_._,___