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.
- 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.
- 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.
- 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@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of JV Dirkes II
Sent: Wednesday, July 23, 2008
1:45 PM
To:
EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] **
Warning ** SimHVAC: Maximum 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!
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