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Re: [EnergyPlus_Support] Re: Exceeding maximum iterations problem

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: Exceeding maximum iterations problem
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Wed, 28 Jul 2004 13:02:46 -0500
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There appears to be a bug affecting this run which combines a VAV system, zone 
exhaust fans, and a return fan.  Eliminating the zone exhaust fans fixes the 
problem.  It might also work to eliminate the return fan.

Mike


On 12 Jul 2004, at 21:39, bsiengineer wrote:

> Zheng,
> 
> Thank you for your response.
> 
> My model has only two zones.  I have previously run this model many 
> times with a constant volume system, and encountered no errors.
> 
> I have manipulated the convergence tolerances with no effect on the 
> iterations.
> 
> My model has no economizer, so the outside temperature limit will not 
> affect it.  I think that in many US buildings the value of 19 is a 
> good choice.  The best temperature limit for a dry-bulb economizer 
> depends on the typical outdoor conditions and the typical return air 
> conditions.  If your return air is 25 C and is normally more humid 
> than the outdoor air then 25 may be a good choice, but I think this 
> would be very unusual.
> 
> Regards, David
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, zhen tian <tianzhen9@y...> 
> wrote:
> > I had this iteration problem tried this method before. 
> >  
> > I found this problem was related to the zone number and zone 
> equipment.  The more zones, and the more equipement in the same zone, 
> the more possibilty of this iteration problem. 
> >  
> > I found that if you set the convege tolerance to 0.00005, and this 
> still appear, even you set minor values, this method will not work.
> >  
> > Try to change the ousiside temperature limit from 19 to 20 or 18, 
> this warning may go away. The example file uses 19 degree C, but I do 
> not think it is correct. It should be around 24 to 26. You can give 
> me a response if it works.
> >  
> > From my perepective view, it will be better for the uses if 
> Energyplus can focus on solve and improve the prolems in the existing 
> models rather than to incorporate new models right now.
> >  
> > By the way, I want to ask if somebody or some company has succeedly 
> used Energyplus for simulating of real big building projects. 
> >  
> > Regards, Zhen
> > 
> > bsiengineer <arch_engel@h...> wrote:
> > Rahul,
> > 
> > Thank you for your help.  I have made several simulation runs with 
> > different convergence tolerances (both increased and decreased 
> > values) on the cooling coil controller and reheat controllers but 
> > these changes have had no effect on the number of iterations 
> reported 
> > in the error file.  Does anybody have any other suggestions?
> > 
> > Thanks,  David
> > 
> > 
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Rahul Chillar 
> > <chillarrahul@y...> wrote:
> > > Hello
> > > This same problem had occured with a user earlier , ........... 
> Max
> > > Iteration errors can be eliminated by increasing the convergence 
> > tolerance
> > > on your controllers
> > >  
> > > For example look at the controller information below and you will 
> > easily figure out how to solve that. If it does not kindly let us 
> > know so that we can look at your file which you uploaded.
> > >  
> > > EARLIER CASE with problems:
> > >  
> > > CONTROLLER:SIMPLE,
> > > Central Cooling Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Reverse, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Cooling Coil Water In, !- Actuator_Node
> > > 0.002, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0000001; !- Min Actuated Flow {m3/s}
> > >  
> > >  
> > > CONTROLLER:SIMPLE,
> > > Central Heating Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Normal, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Main Heating Coil 1 Water Inlet Node, !- Actuator_Node
> > > 0.002, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0000001; !- Min Actuated Flow {m3/s}
> > >  
> > > These values created over 350 Max Iteration warnings. Then the 
> > values were
> > > changed to:
> > > CONTROLLER:SIMPLE,
> > > Central Cooling Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Reverse, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Cooling Coil Water In, !- Actuator_Node
> > > 0.001, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0000001; !- Min Actuated Flow {m3/s}
> > >  
> > >  
> > > CONTROLLER:SIMPLE,
> > > Central Heating Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Normal, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Main Heating Coil 1 Water Inlet Node, !- Actuator_Node
> > > 0.001, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0000001; !- Min Actuated Flow {m3/s}
> > >  
> > > The errors were reduced to over 50 Max iteration warnings.
> > > 
> > > When Values Changed to 
> > > CONTROLLER:SIMPLE,
> > > Central Cooling Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Reverse, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Cooling Coil Water In, !- Actuator_Node
> > > 0.0001, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0; !- Min Actuated Flow {m3/s}
> > >  
> > >  
> > > CONTROLLER:SIMPLE,
> > > Central Heating Coil Contoller 1, !- Name
> > > TEMP, !- Control variable
> > > Normal, !- Action
> > > FLOW, !- Actuator variable
> > > VAV Sys 1 Outlet Node, !- Control_Node
> > > Main Heating Coil 1 Water Inlet Node, !- Actuator_Node
> > > 0.0001, !- Controller Convergence Tolerance: delta
> > > temp from setpoint temp {deltaC}
> > > autosize, !- Max Actuated Flow {m3/s}
> > > 0.0; !- Min Actuated Flow {m3/s}
> > >  
> > >  
> > > ALL MAX ITERATION ERROR ELIMINATED.
> > > Try the same procedure in your file , i am sure they will go 
> away. 
> > These occur because outer loop has higher tolerance set than inner 
> > loop . Hence it is unable to converge. 
> > > If they go away with above change you need not worry about the 
> > results even if you loosen up the tolerance.
> > >  
> > > Thanks
> > > Rahul Chillar
> > > Graduate Research Assistant
> > > Building Systems Laboratory
> > > Univerisity of Illinois UC
> > >  
> > >  
> > >  
> > > 
> > > bsiengineer <arch_engel@h...> wrote:
> > > My simulation is having a problem of exceeding the maximum 
> > iterations 
> > > on the HVAC system.  I am simulating two interior rooms served by 
> a 
> > > single-duct VAV reheat system.  This model has previously been 
> run 
> > > successfully with a single-duct constant volume system.  The 
> system 
> > > is electric preheat and reheat, and purchased chilled water 
> > cooling, 
> > > so it's fairly simple.
> > > 
> > > I will upload my file, Iterations.idf, to the 
> > > folder "Problem_Submittals".  Can anyone help me figure out what 
> is 
> > > going wrong?
> > > 
> > > Thanks!
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
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> 
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> 
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> 
> 
> 
> 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx



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References:
- Re: [EnergyPlus_Support] Re: Exceeding maximum iterations problem
  - From: zhen tian
- [EnergyPlus_Support] Re: Exceeding maximum iterations problem
  - From: bsiengineer

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