[EnergyPlus_Support] questions how COMIS calculates infiltration

[idoebber <idoebber@xxxxxx>]

I am trying to understand how COMIS calculates the pressure difference across 
a crack/opening.  I understand that the pressure difference across an crack on 
an exterior wall is due to stack (temperature) and wind effects.

Stack Effects:
In the summer time when the air is hotter outside, assuming 0 wind speed, the 
outside air pressure should be greater then the inside air pressure thereby 
causing infiltration into the zone.  Conversely, in the winter time with 
colder outside air, assuming 0 wind speed, exfiltration should occur since the 
inside pressure is greater then the outside pressure.  When I did a test run 
on a specific crack in the zone, infiltration occured for both the summer and 
winter.  What am I assuming that is wrong?

Wind Effects:
In a brief design day caculation, I had the wind coming from the south hitting 
directly on a southern wall of my building.  I thought the surface pressure on 
that particular wall should increase with a positive Cp value.  When I 
outputted the surface-averaged wind pressure on the outside surface, the 
values that I got were negative.  I thought these outputed surface-average 
wind pressure was the added pressure on the exterior wall on top of the 
atmospheric pressure of the stagnant outside air.  If this is true, shouldn't 
a wind directly on a surface have a positive surface-average wind pressure.

Finally is there any documentation on how COMIS determines the final pressure 
difference based upon adding together stack and wind effects.  I want to 
understand the relative importance of the two.

Thanks
Ian


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