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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

FeatureForced DraftInduced Draft
Fan LocationInlet (bottom/side)Outlet (top)
AirflowPushes air inPulls air through
RecirculationHigher riskLower risk
Cooling EfficiencyModerateHigher
Energy ConsumptionHigherLower
Maintenance AccessEasier (fan at inlet)Harder (fan at top)
ApplicationsSmall/compact systemsLarge 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.