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RE: [EnergyPlus_Support] Stack Ventilation - Airflow Network


The driving force for air flow is the difference in density between indoor air and outdoor air.� ASHRAE Fundamentals has the equations for calculating stack pressure based on temperature differences and height difference.� The basic air flow equation is flow = coef x pressure^n.� I don’t believe that the airflow network reports pressure.� The network balances the all the pressure differences and flows, so things can get complicated with multiple and different size openings.� For your simple model, and if the windows are the same size, the pressure drop is the same magnitude but opposite sign for the two windows.� You have defined flow coefficients for your windows as part of the network so you can calculate the pressure for each flow.



Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000�main
781.907.9350 direct�
617.285.2162 mobile�
781.907.9009�fax
www.sgh.com



From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of santosh_philip@xxxxxxxxx
Sent: Wednesday, May 07, 2014 4:34 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Stack Ventilation - Airflow Network





I am doing some experiments to see how stack flow ventilation works in Energyplus using Airflow Network. I am primarily interested in Stack ventilation and not in cross-ventilation.



I made a simple box 20' X 30' X 25'(height)

with 2 windows on the 20' elevation, on either side of the box

one window is high and the other window is low



To ensure that I get only stack ventilation, I modified the weather file so that windspeed is 0 m/s at all times.



I looked at output variables

- AFN Linkage Node 1 to Node 2 Volume flow rate (for both windows) - m3/s

- AFN Linkage Node 2 to Node 1 Volume flow rate (for both windows) - m3/s

- AFN Zone infiltration Air Change rate (ach)



These numbers are internally consistent - the volume flow matches the ach.



The ACH varies quite quite a bit through the year going from 0 ACH to 20 ACH

I am trying to understand what makes the ACH change.

What should I be looking at get a sense of this ?



Any advice or pointers ?



Thanx





Santosh Philip








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