Forced draft and induced draft cooling towers are two common types of mechanical draft cooling towers, differing primarily in the placement of fans and airflow mechanisms. Here’s a comparison:
1. Forced Draft Cooling Tower
- Fan Placement: The fan is located at the base (air inlet) of the tower, pushing air into the tower.
- Airflow: High-velocity air is forced upward through the fill media, counterflow or crossflow to the falling water.
- Pressure Conditions: Positive pressure inside the tower.
- Advantages:
- Better suited for high-pressure systems.
- Less recirculation of warm, moist exhaust air.
- Easier fan maintenance (accessible at ground level).
- Disadvantages:
- Higher power consumption (fans work against static pressure).
- Risk of water splash-out due to high inlet air velocity.
- More susceptible to freezing in cold climates.
2. Induced Draft Cooling Tower
- Fan Placement: The fan is located at the top (discharge point) of the tower, pulling air through the fill media.
- Airflow: Air is drawn upward (counterflow) or horizontally (crossflow), creating a negative pressure inside.
- Pressure Conditions: Negative pressure inside the tower.
- Advantages:
- More energy-efficient (fans handle less resistance).
- Better air distribution and reduced recirculation.
- Less water drift loss (lower exit air velocity).
- Disadvantages:
- Fans are exposed to moist, corrosive exhaust air (higher maintenance).
- More prone to recirculation if not properly spaced.
Key Differences Summary
| Feature | Forced Draft | Induced Draft |
| Fan Position | Bottom (air inlet) | Top (discharge) |
| Airflow Mechanism | Fan pushes air in | Fan pulls air through |
| Pressure Inside | Positive | Negative |
| Energy Efficiency | Less efficient (higher power) | More efficient |
| Maintenance | Easier (ground-level fans) | Harder (exposed to moisture) |
| Water Drift | Higher risk | Lower risk |
| Cold Climate Use | More freezing risk | Better performance |
Which One to Choose?
- Forced Draft: Preferred for high-pressure applications, where fan accessibility is critical.
- Induced Draft: More common in large industrial applications due to better efficiency and lower drift losses.