Effect of Exterior Conditions.
The spaces between buildings will
condition the air before it enters through building openings. If possible,
the airflow approaching the building inlet should not pass closely over a
large hot surface (such as a sunlit asphalt parking lot) which will heat the
The Vertical Location in the Wall. The stack effect in most
residential buildings is negligible and completely overwhelmed by even modest
wind effects. If stack ventilation is used, openings must be placed both low
and high in the building. While the movement of air as a result of the stack
effect may be adequate for fresh air supply, it is rarely sufficient to create
the appreciable air movement required in hot zones to provide thermal comfort.
Schemes that attempt to create forced stack ventilation by heating mass within
the stack should not be used.
For wind-driven ventilation, outlet height has little influence on
interior airflow, but inlet height has a great effect on the airflow pattern
in the room. Positive pressures built up on the windward face of the building
can direct the airflow up to the ceiling or down to the floor of the room.
These positive pressures are related to the area of the windward face. Thus,
a window located high on the wall directs airflow up to the ceiling because
the positive pressure built up on the building face is larger below the
window than above it (see Figure 29).
There is usually an abrupt drop (up to 25 percent) in airspeed
below the level of the inlet sill (see Figure 29). The sill height may
significantly alter the air velocity at certain levels while only slightly
affecting the average airspeed in the whole room. Therefore, for body