RE: [EnergyPlus_Support] Re: AFN Node Pressure Distribution & Air Density

[Lixing Gu <gu@xxxxxxxxxxxx>]

Tobias:

The existing AirflowNetwork model does not address the thermal chimney yet.
A horizontal opening is manly used to introduce a circular flow between two
zones.

Thanks.

Lixing  

-----Original Message-----
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of tobiasschulzeoooitu
Sent: Monday, May 03, 2010 7:49 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: AFN Node Pressure Distribution & Air
Density

Dear Lixing,
Thank you for your prompt answer. I have one more question about vertical
airflow in the AFN which for I first should describe my model a little.
I try to connect several floors of a high rise building to a common used
thermal chimney. So this stack has openings on different heights to
different zones. I simulated the case 1) with one chimney zone 2) multi
chimney zones (one per floor) connected by horizontal openings (90deg Cd=1).
With the one zone chimney i had a faster decrease of flow rates from bottom
to higher floors than with the multi zone model.
Anyway, my question is, if it is a meaningful way to connect more than 2
zones vertically by horizontal openings? What are the restictions here?
There is one example file available, where only two zones are stacked
(AirflowNetwor_Multizone_HorizontalOpening.idf). Would the model work, if
more zones are stacked, for example in stairways, elevator stack, atrium or
double skin facade? I wonder if the AFN Restriction In-Out-Ref also counts
for horizontal openings connections or if it was written before the
introduction of horiz.open. in E+.

"Air circulation and/or air temperature stratification within thermal zone.
For example, you should not try to divide a high space, such as an atrium,
into subzones separated by artificial horizontal surfaces that have cracks
or openings with the expectation that AirflowNetwork will give you a
realistic temperature in each subzone and/or a realistic air flow between
subzones."

If you would know a reference dealing with a similar problem, that would be
also helpful for me.
Best regards,
Tobias



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Lixing Gu <gu@...> wrote:
>
> My answers are under your questions.
> 
> 1a) Where is the Zone_Node situated Floor/ceiling/center?
> 
> A: Center.
> 
> 1b) Is there a link to the room-air-model (temperature at a specific
height
> - if not mixed air)?
> 
> A: No.
> 
> 1c) could you please give the formuala for the zone 'AirflowNetwork Node
> Total Pressure'? Especially how is the zone static pressure calculated?
> 
> A: The model uses the total pressure, The static pressure is not
calculated
> alone. The section of AirflowNetwork model in the Engineering Reference
> provides detailed information.
>  
> 2) For the calculation of the air density i used following formula, which
> wasn't found in the eng.reference - but it gives slightly different
results:
> 
> &#961;=(P_atm (1+W_air))/(461,518(T_air+273,15)(W_air+0,62198))
[kg/m3]
> &#961; = Air density [kg/m3]
> Patm = Outdoor barometric pressure at ground level [Pa]
> Wair = Air humidity ratio [kgWater/kgAir]
> Tair = Air Temperature [°C]
> 
> A: the following equation is used to calculate air density
>       rhoair = pb/(287.d0*(tdb+KelvinConv)*(1.d0+1.6077687d0*w))
> 
> Lixing
> 
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> 
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