CHAPTER 5. MECHANICAL VENTILATION COOLING SYSTEMS
5.1 GENERAL. Mechanical ventilation cooling systems, better known as "Whole
House Fans" are ventilation systems that rely on "wind chill" or evaporative
cooling of the skin for its cooling effect.
The building is normally ventilated at the rate of 30 to 60 air changes
per hour for best cooling effect. Air movement velocity is normally limited
to 100 feet per minute (fpm) or less in residences and office areas as
higher velocities will cause light objects to flutter and move and produce
annoying drafts. In industrial applications, local velocities up to 4,000
fpm may be used. However, velocities greater than 1,000 fpm may disrupt the
performance of nearby local exhaust systems and care must be taken to direct
air motion to prevent such interference. The current edition of Industrial
Ventilation, by the American Conference of Governmental Industrial
Hygienists, has a chapter on ventilation for heat control and should be
consulted regarding velocities and air movement in the industrial workplace.
For dry bulb temperatures over 95 F, ventilation cooling does not
appear to work. Current practice is to limit its application in offices and
residences to temperatures of 85 F.
5.2 FANS AND INSTALLATION PRACTICES. The fans used for mechanical
ventilation are generally propeller types and may be direct or belt driven,
have sealed bearings or bearings requiring periodic oiling. Multiple speed
arrangements are also available. The fans may be installed directly on an
outside wall, in a penthouse on a flat roof, or in a hallway which vents
into an attic as shown in Figures 5-l and 5-2.
The net free area of the exhaust opening must be as large or larger than
the area of the fan in order for the fan to operate properly.
installations will have shutters that automatically open and close with the
operation of the fan. For proper operation, the net free area of the
shutter opening should be equal to or greater than the area of the fan.
Roof Mounted Fan With Penthouse