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[EnergyPlus_Support] Re: HVAC loop convergence exceeded...
Hi Sankar,
Thanks for your reply.
Yes I have already been disactivating some autosized values first
because it didn't give the values I wanted to match the installation
operating typical flows and values.
As a result, I still have a mix between autosized and given values
but now most of them are given.
I think you are right, the problem must come from the chiller because
it started when I arranged them in parallel so, at some point (loads)
they might not know if they should turn on or not. Problem is that I
cannot give a minimum water flow value for their water pump because
then, the simulation crash (flow equations do not converge anymore,
that's one thing I cannot have exactly as it performs in reality).
System description:
Pump control is continuous and max flow rate is given, set as active
component
Loop control is typical (demand side gives supply side setpoint
features that drive pumps and chillers operation). It targets my
plant sizing parameters for the DT and Tsupply. As a result I have
quite realistic operating values (match quite well what installation
manager says, only problem is that calculation time!!). Chillers are
set as passive component in each branch.
It is installation with AHU at each floor, precooling air at 26°C.
Then, fancoils object are terminal units to cool down the zones at 26°
C. They only draw room air.
Also, there are more than 30 zones, maybe is a problem but I don't
think so because heating season does not have this problem.
As another group member suggested, I changed the maximum iteration
number and time step. Of course, if I set the timestep of system to
match the timestep of zones (input=1) it reduces convergence excess
problems but they remain.
Maybe it is the last chiller (that is less used) that causes the
problem? what do you think?
I have another problem for heating as well if you have the magic
idea: I created the air to water heat pump for heating. It performs
well. Though, if I want to create them in parallel I can't have
variable flow operation anymore (something is telling the loop to
perform in constant flow and I do not know what). When I plug them in
series, no problem, it works well. Any idea?
Thank you for your help
Best regards
Aymeric
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Sankar Padhmanabhan
<sankar.padhmanabhan@...> wrote:
>
> Hi Aymeric,
> Is the loop autosized? If yes do you have autosizing in all the
> components? There could be a problem when you have autosizing and
hard
> number mixed up in the loop. What control type are you using for
the
> loop. In variable flow configurations, the simulation some times
get
> stuck at some loads. If that happens the chillers tend to turn
OFF/ON in
> between iterations. Give a brief description how you have your
system
> modeled as in what type of pump control, loop control etc, which
might
> help in identifying the problem.
>
> Thanks
> Sankar
>
> aymericnovel wrote:
> >
> > Good morning,
> >
> > I have a chilled water loop with 4 chillers in parallel. Each
branch
> > has a variable speed water pump. The whole water loop is meant to
> > perform with variable water flow to adapt to the load.
> >
> > It looks like it works. Still, the simulation takes a lot of time
> > and "HVAC loop maximum iteration exceeded" error message occurs a
lot.
> > I am pretty sure it is the mass flow balance that does not
converge but
> > I do not find a solution to solve this.
> >
> > Does anyone see what would be the trick? (where is convergence
criteria
> > of massflow by the way?)
> >
> > Thank you,
> > Aymeric
> >
> >
>
> --
> Sankar Padhmanabhan
> Graduate Research Assistant
> Ph.D Student
> Mechanical & Aerospace Engg
> Oklahoma State University,
> Stillwater, OK-74078
> Ph:405-744-2410 (O)
>
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