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Re: [EnergyPlus_Support] Exceeding maximum iterations problem

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@xxxxxxxxxxx> 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!




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Thanks 
Rahul Chillar 
Grad Student 
Building Systems lab
Univ Of Illinois Urbana Champaign

		
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