Forced Draft (FD) Vs Induced Draft (ID) cooling towers
1. Forced Draft Cooling Tower
- Fan Location: Fan is placed at the air inlet (bottom or side) of the tower.
- Airflow: The fan pushes (forces) air into the tower, and it exits through the top.
- Characteristics:
- Smaller footprint → compact design.
- Positive pressure inside tower → higher risk of drift (water droplets carried away).
- More prone to recirculation (discharged hot, moist air getting sucked back into the tower).
- Fan is located at the air entrance → easier access for maintenance.
- Less efficient air distribution compared to induced draft.
- Higher energy consumption since fans work against internal resistance.
- Applications: Small installations, HVAC cooling towers, where compactness is important.
2. Induced Draft Cooling Tower
- Fan Location: Fan is mounted at the air outlet (top) of the tower.
- Airflow: The fan pulls (induces) air through the tower, discharging it upward at high velocity.
- Characteristics:
- Negative pressure inside tower → reduces drift losses.
- Hot, moist air is expelled at high velocity upward → minimizes recirculation.
- More uniform airflow across the fill → better cooling efficiency.
- Slightly larger footprint and higher structural requirements.
- Fan operates in hot, moist exhaust air → may require more robust fan/motor materials.
- More energy-efficient than forced draft for large towers.
- Applications: Power plants, petrochemical plants, and large industrial cooling loads.
Quick Comparison Table
| Feature | Forced Draft | Induced Draft |
| Fan Location | Inlet (bottom/side) | Outlet (top) |
| Airflow | Pushes air in | Pulls air through |
| Recirculation | Higher risk | Lower risk |
| Cooling Efficiency | Moderate | Higher |
| Energy Consumption | Higher | Lower |
| Maintenance Access | Easier (fan at inlet) | Harder (fan at top) |
| Applications | Small/compact systems | Large industrial systems |
- Forced draft = compact, easier to maintain, but less efficient and more prone to recirculation.
- Induced draft = widely used in industry due to better cooling efficiency and reduced recirculation.