Induced Draft Cooling Tower Fan Blade Angle

Induced Draft Cooling Tower Fan Blade Angle (Blade Pitch)

The fan blade angle in an induced draft cooling tower controls how much air the fan moves through the tower. It directly affects cooling capacity, motor amperage, noise, and energy consumption.

What Is Induced Draft Cooling Tower Fan Blade Angle?

* The angle between the fan blade chord line and the plane of rotation

* Measured in degrees (°)

* Set and checked at 70–75% of blade radius from the hub

* Must be identical on all blades

Typical Induced Draft Cooling Tower Fan Blade Angle Range

Application	Normal Range
HVAC cooling towers	8° – 12°
Industrial / process towers	10° – 16°
Large high-efficiency fans	12° – 18°

> ⚠️ Always follow the fan manufacturer’s data. Exceeding limits can overload the motor or gearbox.

Effect of Changing Induced Draft Cooling Tower Fan Blade Angle

Increase Blade Angle

* ↑ Airflow

* ↑ Cooling performance

* ↑ Fan power & motor current

* ↑ Noise and vibration (if excessive)

Decrease Blade Angle

* ↓ Airflow

* ↓ Cooling capacity

* ↓ Power consumption

* ↓ Noise

Power & Current Relationship

Fan power increases approximately with the cube of airflow:

                                                                  P ∝ Q³

A small increase of 1–2° can raise motor current by 10–25% depending on system resistance.

How to Measure Induced Draft Cooling Tower Fan Blade Angle

Tools: Digital inclinometer or blade pitch gauge

Procedure:

1. Lock out & tag out the fan motor

2. Position blade horizontally

3. Measure at 70–75% blade radius

4. Use the fan hub reference surface as zero

5. Check every blade (tolerance typically ±0.2°)

How to Adjust Induced Draft Cooling Tower Fan Blade Angle

1. Loosen blade clamp bolts evenly

2. Set blade to target angle

3. Tighten bolts to specified torque

4. Re-check angle after tightening

5. Verify blade tracking and balance

Common Problems Due to Incorrect Induced Draft Cooling Tower Fan Blade Angle

Problem	Likely Cause
Motor overload / tripping	Blade angle too high
Poor cooling	Blade angle too low
High vibration	Unequal blade pitch
Excessive noise	Over-pitched blades

Practical Adjustment Guidelines

* Change angle in ≤1° increments

* After adjustment, measure motor amperage

* Keep running amps ≤ 90–95% of motor FLA

* Clean fill and drift eliminators before increasing pitch

Typical Manufacturer Guidance

* Marley axial fans: ~10°–14°

* EVAPCO fans: ~11°–16°

* BAC fans: ~9°–15°