ASHRAE Journal - February 2014 - 46

Column BUILDING SCIENCES

(Photos 1 and 2). Just by looking at
buildings you could often tell where
the neutral pressure plane was.
Many two-story houses had frost on
the second floor windows, whereas
the first floor windows were clear-
infiltration through the lower windows and exfiltration through the
PHOTO 1 (LEFT) Peeling Paint "Tell." Where is the neutral pressure plane in this photograph? Neat, eh? Air exfiltrating
above the neutral pressure plane typically carries interior moisture. This moisture is deposited in the wall leading
upper windows-neutral pressure
to peeling paint problems. Below the neutral pressure plane, air is infiltrating from the exterior, carrying little or
plane between the two.
no moisture. Legend has it that in this building an old oil boiler with a large active chimney was replaced with a
sealed combustion condensing gas boiler lowering the neutral pressure plane. Of course, this picture could also
When we go to high-rise buildbe explained by rain deposition, but I am sticking with the air leakage neutral pressure plane story because it is so
ings the principles remain the
cool. PHOTO 2 (RIGHT) Stack Effect Damage. This is stack effect air leakage leading to moisture induced damage for
same as do the problems. Stack
sure. Not rain. Why? Only happens in winter when it does not rain. Efflorescence. It came from inside and ate your
building-wooo-scary stuff, boys and girls.
effect-driven airflows in tall
buildings compromise smoke
control and fire safety, adversely affect indoor air
Basically, you turn a 10-story building into 10
quality and comfort, as well as increase operating
one-story buildings that are stacked on top of one
costs for space conditioning energy (Figure 7 ). The
another. I wrote about this much earlier in this very
air in lower units ends up in the upper units. I guess Journal.4,**
Achieving compartmentalization is not easy. You have
that is why folks in the upper units pay more for the
to think three dimensionally, and treat your interior
privilege.
walls like exterior walls (Figure 9). Back in the day some
By isolating the units from each other and from corridors, shafts, elevators and stairwells, stack effect-driven
interior airflows can be controlled (Figure 8). Today we
Reduced Individual Unit Stack Effect
call this compartmentalization. The most elegant argument for compartmentalization of tall buildings came
from Handegord.3
Stack Effect Flow Out
(Exfiltration)
Poutside Drops
With Height
Faster than Pinside

Pinside Drops with
Height Slower
than Poutside
Neutral
Pressure
Plane

Stack Effect Flow In (Infiltration)
FIGURE 7 Stack Effect in a Tall Building. Stack effect-driven airflows in tall build-

ings compromise smoke control and fire safety, adversely affect indoor air quality
and comfort as well as increase operating costs for space conditioning energy.
The air in lower units ends up in the upper units. I guess that is why folks in the
upper units pay more for the privilege.

FIGURE 8 Compartmentalization. Basically, you turn a 10-story building into 10 one-

story buildings that are stacked on top of one another. By isolating the units from
each other and from corridors, shafts, elevators and stairwells, stack effect-driven
interior airflows can be controlled.

**Make no mistake about this-I was channeling Gus-this is not my stuff. I just grabbed onto it earlier than most. Gus was on to this very early; he just didn't always write things down and get them published
and peer reviewed in a timely fashion. He finally wrote it all down in his 2001 paper but I first heard it from him when I took his class at the University of Toronto in 1982, and he was talking about it much
earlier than that. I was pushing compartmentalization when I first started working in the United States in 1986. I still smile when I remember the arguments with the Chicago high-rise boys in the late '80s.
46

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