Forced Draft and Induced Draft Air Cooled Heat Exchangers (ACHEs)
two of the most common types used in industrial cooling:
1. Airflow Mechanism
| Feature | Forced Draft ACHE | Induced Draft ACHE |
| Fan Position | Below the tube bundle | Above the tube bundle |
| Airflow Direction | Fan pushes air upward through tubes | Fan pulls air downward through tubes |
| Pressure Zone | Positive pressure (air forced in) | Negative pressure (air sucked out) |
2. Performance & Efficiency
| Aspect | Forced Draft | Induced Draft |
| Heat Transfer Efficiency | Slightly lower (uneven air distribution) | Higher (more uniform airflow) |
| Hot Air Recirculation | More likely (hot air can loop back) | Less likely (fan disperses hot air upward) |
| Power Consumption | Higher (fan fights static pressure) | Lower (fan works with natural convection) |
| Suitability for High Temp | Less efficient (hot air exits slowly) | Better (rapid hot air removal) |
3. Maintenance & Durability
| Factor | Forced Draft | Induced Draft |
| Fan Accessibility | Easier (fan at ground level) | Harder (fan elevated) |
| Tube Exposure | Cooler air enters, reducing thermal stress | Tubes exposed to hotter air (potential corrosion) |
| Motor Life | Longer (cooler operating environment) | Shorter (exposed to hot exhaust air) |
| Weather Protection | Tubes shielded from rain/snow by plenum | Tubes exposed to elements |
4. Structural Design
| Feature | Forced Draft | Induced Draft |
| Plenum Chamber | Larger (to distribute pushed air) | Smaller (suction effect evens airflow) |
| Noise Levels | Louder (fan noise directed downward) | Quieter (fan noise dispersed upward) |
| Footprint | Compact (fan below tubes) | Taller (fan above tubes) |
5. Typical Applications
| Forced Draft ACHE | Induced Draft ACHE |
| Low/medium-temperature processes | High-temperature applications (e.g., refineries, power plants) |
| Where fan maintenance is critical | Where heat efficiency is prioritized |
| Less corrosive environments | Better for corrosive fluids (hot air exits faster) |
Which One to Choose?
- Pick Forced Draft if:
- Easy maintenance is a priority.
- Process temperatures are moderate.
- Noise control is less critical.
- Pick Induced Draft if:
- High heat transfer efficiency is needed.
- Hot air recirculation must be minimized.
- The environment is corrosive or high-temperature.
Quick Summary Table
| Criteria | Forced Draft | Induced Draft |
| Fan Position | Below tubes | Above tubes |
| Airflow | Push | Pull |
| Efficiency | Lower | Higher |
| Maintenance | Easier | Harder |
| Noise | Louder | Quieter |
| Best For | Moderate heat | Extreme heat |