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Re: [EnergyPlus_Support] Geometry, Exhaust Fan, AFN

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Geometry, Exhaust Fan, AFN
From: Lixing Gu <gu@xxxxxxxxxxxx>
Date: Wed, 27 Sep 2006 10:13:09 -0400
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Kristin:

The AirfloeNetwork control option of Multiozne without Distribution 
simulates multizone airflows driven by outdoor wind only (no involvement of 
forced air). The option of Multiozne with Distribution simulates multizone 
airflows driven by wind and forced air, including duct leakage and duct 
energy losses. The Airflow Network System section in the Input Output 
Reference provides detailed description on p. 582.

The AirflowNetwork model dose not have any restriction of time step. The 
minimum time step is 1 minute restriceted in HAVC system simulations. Since 
windows are controled by temperature using the AirflowNetwork model in your 
case, the openess is determined by the temperature difference between indoor 
and outdoor, and availability schedule. The openess is not controlled by 
HVAC system. Thereofre, it is possible that windows are open and HAVC system 
is on at the same time. Warnings are issued to let users be aware.

I agree with you to have different monthly vantilation temperature setpoints 
in order to eliminate warnings. You may run simulations twice for June and 
Sep control. You can get hourly HVAC system on/off schedule from the first 
run. Then set 0 in the availability schedule when the HVAC system is on. Run 
the simulation again using the revised availability schedule.

Hope my reply helps.

Lixing
----- Original Message ----- 
From: "Kristin Field" <fieldkm@xxxxxxxxx>
To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Tuesday, September 26, 2006 3:12 PM
Subject: [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@...
>>
>
>
>
>
>
>
> 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
>
>
>
>
>
>
>
>
>
>
> 




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References:
- [EnergyPlus_Support] Geometry, Exhaust Fan, AFN
  - From: Kristin Field

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