Re: [EnergyPlus_Support] Errors in some zones and not others

["Michael J. Witte" <mjwitte@xxxxxxxx>]

On 7 Apr 2006 at 18:46, Sam Roose wrote:

> I have uploaded a file named 18_manager_changes that when run in Version
> 1.2.3.031 gives me three errors.
> 
> 1) Calculated design heating load for zone = OUTPATIENT 2 is zero. Check
> zone sizing and zone thermostat inputs.
>
>     The specification for OUTPATIENT 2 is no different to the other zones
> with respect to zone sizing and zone thermostat inputs. Hopefully, this
> isn't due to the use of multiple air loops.
> 


1.  This means the zone has no need for heating on the heating design day.  The 
zone sizing calculation only relies on the building envelope, thermostat, and 
zone sizing objects.  It knows nothing of the HVAC system at this point in the 
calculation, including any fresh air the HVAC system may be introducing.  So, 
this is a loads balance issue for the winter design day.  If I'm reading the 
drawing and inputs correctly, this zone is a large, part interior, part 
exterior zone with a small amount of glass.  So this result may be correct, but 
you should double check the internal gains.

The zone loads are used only to determine the air volume flow rate for that 
zone.  The system coils are then sized to deliver the specified supply air 
temperatures are that flow rate, so the coil load will include the outside air 
loads.
 
> 2) Maximum iterations exceeded for three different air loops: Zone 7, Zone 8
> and Zone 23, all quite large zones and mostly internal to the building. Why
> is this?

2. Max iteration errors indicate the system could not converge on a solution.  
This can be due to inconsistent controls causing battling, or a variety of 
other reasons.  I see two problems in the controller:simple inputs:

2a.  There are HUMIDISTAT and SET POINT MANAGER:SINGLE ZONE MAX HUM objects, so 
I presume you want humidity control.  All of the cooling coi controllers are 
currently set for Control variable = TEMP.  For humidity control these must be 
set to TEMPandHUMRAT.  They are currently controlling just for the dry bulb 
setopint.  (I've posted a suggestion to warn of this condition.)

2b.  The supply duct heating coil controllers (I'm presuming these are reheat 
for the humidity control) are using "Zone 4 Cooling Coil Outlet Node" as the 
control node, but that is the air inlet to the coil.  This most likely why 
there are max iteration errors and poor control.  To fix this, change the 
control node to be the heating coil air outlet node (e.g. Zone 1 Air Loop 
Outlet Node).  This node also needs a setpoint.  In the SET POINT 
MANAGER:SINGLE ZONE REHEAT, the "Name of the set point Node or Node List" needs 
to be a node list which lists both the cooling coil outlet node and the air 
loop outlet node (which is the heating coil outlet).

2c.  I am a bit puzzled at this system configuration.  The way it is described 
now, it appears that the cooling coil and heating coil in the main air loop 
branch will do all of the control and the zone-level reheat coil is 
unneccessary.  

Mike


> 
> 3) Temperatures out of comfort range, despite everything being autosized.
> Mostly it is a result of overheating due to this building having high
> internal gains. However, the number of hours temperatures are out of range
> is high in some cases. Can this be reduced?
> 
> Thanks in advance,
> 
> Sam Roose
> 
> 
> 
> 
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> 
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> 
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> 
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> "search" button.
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 
> 


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





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