wo general classifications of air-cooler fans are:
a) forced draft type where air is pushed across the tube bundle;
b) induced draft type where air is pulled through the bundle
Forced draft should be selected for all normal applications. Amongst other reasons, the accessibility of fans, actuators and drivers is much better for maintenance and there is thus a strong preference for this arrangement.
Forced draft shall be selected for critical and condensing duties where the difference between the design product outlet temperature and the design air inlet temperature is 15°C or higher.
Forced draft shall be selected for all cooling duties where air outlet temperatures would be higher than those specified as limiting for the induced-draft arrangement. For critical cooling or condensing duties where the product outlet temperature falls below a point 15°C above the design air inlet temperature (*), induced draft may be considered providing the air outlet temperature will not rise to a level higher than is acceptable for the fan, fan hub and bearings for the greasing system and for all structural components exposed to the hot air stream. The degree of acceptability is subject to the Company’s approval.