Most air-cooled exchangers are forced drafts which are easier to maintain. In forced draft arrangement fans are mounted bellow tube bundle. Forced draft air cooled heat exchangers require slightly less horse power moving less volume of air.
Advantages Of Forced Draft Lower horsepower requirements if the effluent air is very hot.
Better accessibility of fans and upper bearings for maintenance.
Better accessibility of bundles for replacement.
Accommodates higher process inlet temperatures.
Disadvantages Of Forced Draft Less uniform distribution of air over the bundle.
Increased possibility of hot air recirculation, resulting from low discharge velocity from the bundles, high intake velocity to the fan ring, and no stack.
Low natural draft capability on fan failure.
Complete exposure of the finned tubes to sun, rain, and hail, which results in poor process control and stability.