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[EnergyPlus_Support] Outside temperature limit
Hi, David:
About the outside temperature limit, I have a question. For air system, the supply air temperature is around 13 to 16 degree C, the return air temperature is around 25 is the indoor temperature is around 24. To my understading, if the outside temperature is under return air temperature, you can use "free cooling". If the outside temperature is between supply and air temperature, say 13 to 25 degree C, you can use 100 percent outside air for cooling, it will save energy for mixing air.
So could you tell me what is unusual?
Thanks.
Zhen
bsiengineer <arch_engel@xxxxxxxxxxx> 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!
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