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[EnergyPlus_Support] Geometry, Exhaust Fan, AFN



Michael, Linda, and Lixing,

Thank you so much for your suggestions - they were very helpful!!

Lixing, eliminating the exhaust fan has improved the runs.  I'm glad 
you told me about the multizone w/o distribution option, though.  In 
that scenario, I get to keep my exhaust fan.  Could you (or someone 
else) tell me - does "multizone w/o distribution" mean that the 
pressure differences, etc. that characterize the airflow network 
simulations are simulated for the zone air and wall/window surfaces, 
but not for the air distribution itself (i.e., ducts, coils, and 
fans)?  Does this just mean that duct leakage, etc. is simulated as 
it would have been prior to the airflow network capability?

New question: does the airflow network simulate every 5 minutes?  I'm 
getting errors that say that a certain 5-minute interval has both the 
HVAC on and windows open at the same time (nat. vent. - I have mine 
on "temperature" control).  My runs are only going hourly right now, 
though.  When I adjusted the temperature schedule, it did affect how 
frequently this problem occurred, but it still never got rid of it.  
Some info. in case this helps:

*I have very large areas open for natural ventilation, but I really 
don't want to change this (as it's specified for my project).  It's 
possible that when the windows open, the zone conditions change 
relatively quickly due to the large exposure to the outdoors.

*My heating setpoint is always 21.7C, and my cooling setpoint is 
always 24.4C.  Cooling is enabled June-Sep. only, and heating is 
enabled all months except July&Aug.

*The closer I set the nat. vent. temp. to 24.4C, the fewer 
simultaneous-nat-vent-HVAC errors I got.  However, the errors occured 
on Feb. 1 in the afternoon, and cooling is not enabled in Feb.  The 
simultaneous HVAC/natvent error has to be referring to heating.  This 
could be a good reason to have different monthly values for the 
natvent temp. schedule, but I wouldn't be sure how to handle June & 
September, when both heating and cooling are enabled - especially if 
the large window area means that my zone temperatures change too 
quickly during natvent.

Thanks again for any/all help!

--Kristin

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
<mjwitte@...> wrote:
>
> Regarding the view factor area, the MAIN zone description has 
internal mass 
> with an area of 333 m2, and the total area of the other surfaces in 
the zone is 
> 338 m2.  The EnergyPlus view factor calculation struggles to define 
an 
> enclosure when the area of one surface is equal to or greater than 
the sum of 
> the areas of the other surfaces.  In this case, it is very close 
and happens to 
> fail.  Splitting the one large internal mass surface into two 
smaller ones 
> eliminates the view factor error.
> 
> Mike
> 
> 
> On 24 Sep 2006 at 8:50, Kristin Field wrote:
> 
> > If anyone could help me with the following errors I've been 
> > receiving, I would be *very* grateful.
> > 
> > Background: My file, which I'll upload shortly (titled 
> > BAB_Baltimore_092306.idf), is supposed to represent a simple 
30'x30' 
> > house that's 16' tall with a 4-sided, unconditioned attic on top 
(2 
> > triangles and 2 rectangles).  The attic peak is at 23.5'.  This 
house 
> > should have typical DX cooling and furnace heating, with natural 
> > ventilation when weather permits.  I have attempted to implement 
a 
> > simple airflow network model with several cracks for infiltration 
and 
> > operable windows/doors for natural ventilation.  To the greatest 
> > extent possible, I followed the simple house airflow network 
example 
> > file with EP-V1.3.0.
> > 
> > First (Severe) Error: I get the following geometry error after 
having 
> > experimented with several different view factor combinations and 
> > after thoroughly reviewing what seem to be logical vertices to me.
> > 
> > "View factors not complete. Probably bad surface descriptions in 
> > zone="MAIN ZONE". Enforced reciprocity has tolerance (ideal is 
0.0)
> > =3.0292E-002. Enforced value is not within normal convergence 
> > tolerance (<.0001)."
> > 
> > Second (Fatal) Error: I get this message after EP aborts 
following 
> > the "Initializing HVAC" line in the command prompt window.  I 
have 
> > also tried several combinations of new values for the parameters 
it 
> > suggests - including increasing and decreasing them by several 
orders 
> > of magnitude.  No effect except increased processing time in some 
> > cases.  The audit file doesn't tell me anything.  I actually 
wonder 
> > if the first error is influencing EP's ability to converge here.
> > 
> > "Too many iterations (SOLVZP) in AirflowNetwork simulation
> > AirflowNetwork: SOLVER, Changing values for initialization flag, 
> > Relative airflow convergence, Absolute airflow convergence, 
> > Convergence acceleration limit or Maximum Iteration Number may 
solve 
> > the problem. Occurrence info: Occurrence info=STERLING VA USA 
TMY2-
> > 93738 WMO#=724030, 01/01 01:00 - 02:00
> > AirflowNetwork: SOLVER, The previous error causes termination."
> > 
> > Any ideas/help appreciated - thanks!
> > 
> > --Kristin Field
> > 
> > 
> > 
> > 
> > 
> > 
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> > 
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> > 
> > Attachments are not allowed -- please post any files to the 
appropriate folder
> > in the Files area of the Support Web Site.
> > 
> > EnergyPlus Documentation is searchable.  Open EPlusMainMenu.idf 
and press the
> > "search" button.
> >  
> > Yahoo! Groups Links
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> 
> 
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support      
> EnergyPlus-Support@...
>






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