CHAPTER 3. NATURAL OR GRAVITY VENTILATION SYSTEMS
3.1 GENERAL. Natural ventilation systems do not depend upon fans and motors
to move air. Rather, wind velocity and the natural buoyancy of warm air
provide the motive force for moving air.
3.2 WIND-OPERATED FANS. Figure 3-l shows a turbine-type exhauster with a
fan attached to a turbine. As wind passes the turbine, it turns and drives
the fan to remove the warm air. The driving force on the fan is minimal,
and for effective operation, the bearings that allow free rotation must be
clean and lubricated. The wind-powered turbine fan sitting stationary atop
a roof on a windy day is a testimonial to poor maintenance of bearings.
3.3 GRAVITY VENTILATORS. Gravity ventilators have no moving parts. They
merely provide the necessary openings to allow warm air to rise in a
building and exit through the roof, and for cooler air to enter from a lower
Figure 3-2 shows a gravity ventilator which may be located on a
rooftop. The taller the building, the better a gravity ventilation system
may be expected to operate.
Another type of gravity ventilator is the louvered roof monitor, shown
on figure 3-3, which provides an exit path for the warm air in the building.
One of the advantages to gravity systems is the low maintenance
Semiannual inspection will reveal any need for painting or
repair. Dampers should be closed at the beginning of each winter season,
and opened prior to the need for summer ventilation.