Forced Draft air cooled heat exchangers
- Fans are located below the tube bundles
- Air is pushed across the finned tube surface
- Better accessibility to the fan for maintenance and fan-blade adjustment
- Fan and V-belt assembly are not exposed to the hot-air stream that exits from the unit
- Less structural support is required, and capital cost is lower.
- Longer mechanical life
- In theory, the primary advantage of the forced-draft unit is that less power is required. This is true when the air temperature rise exceeds 54°F (30°C), because the fan is pumping denser air.
Induced draft air cooled heat exchangers
- Fans are located above the bundle
- Air is pulled across the finned tube surface
- Since air velocity approaching the bundle is relatively low, it provides more even distribution of air across the bundle
- Better suited for exchangers designed for a close approach of product outlet temperature to ambient-air temperature
- Less likely to recirculate the hot exhaust air, since the exit air velocity is much higher than the forced-draft unit
- In a service in which sudden temperature change would cause upset and loss of product, the induced-draft unit gives more protection in that only a fraction of the surface (as compared with the forced draft unit) is exposed to rainfall, sleet, or snow.
- Will transfer more heat by natural convection with fans off because of the stack effect.