Variable Frequency Drives for Cooling Towers
Cooling towers are widely used and industry. Cooling towers main function to cool the air from atmosphere and remove the heat by evaporation of water. Cooling towers varies in designs but the fans used in it are used to cool down temperature by cold water. Mains operations of cooling fan requires start and stop function, Variation in the speed of fan, and some time variation in direction too; under certain atmospherically conditions. Cooling tower is used in industries such as Oil refineries, Pharmaceutical plants, thermal power, food processing plants Petrochemicals plants and HVAC systems (in malls, exhibitions halls, corporate buildings, etc.). Cooling tower fans are basically of two types Induced draft and natural draft.
Need of VFD in Cooling Tower Fans
- Variable speed is required at different atmospheric conditions (air temperature).
- Rotational direction of Fan may change due to phase change in mains supply and this can lead Fans to malfunction its operation. In traditional system additional starter is required or a operator is required to correct it.
- VFD avoids high inrush current and jerky starts.
- VFD avoids the necessity of mechanical and electrical brakes
- Pitch of the blades may need to be adjusted according to the season (air temperature) to prevent motor overloading due to cold, dense air
- Increased maintenance costs due to power train shock/stresses and motor starter replacement
Features required in VFD
- Soft Start Stop (reduces Mechanical Wear and tear.)
- Sensorless vector Control
- Auto energy saving Feature for energy saving purpose
Energy saving is most important role of VFD in this application. Due of continuous changes in weather and air temperature speed of the fan is required to change. Due to law of affinity whenever there is change in speed power changes in cube with respect to speed.
N = Speed of Motor
P = Power consumption of motor
Law of affinity states that
N α P3
So even if speed is decreased by 20% power consumption of motor reduces by around 40% – 50%. So applying a VFD is very cost saving.
Fuji, ABB, Danfoss, Hitachi and Delta
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