GE AF-600 FP Design Manual page 25

AF-600 FP Design Guide
2.7.17 Cooling Tower Fan
Cooling Tower Fans are used to cool condenser water in water cooled chiller systems. Water cooled chillers provide the most efficient means of creating chilled
water. They are as much as 20% more efficient than air cooled chillers. Depending on climate, cooling towers are often the most energy efficient method of cooling
the condenser water from chillers.
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They cool the condenser water by evaporation.
The condenser water is sprayed into the cooling tower onto the cooling towers "fill" to increase its surface area. The tower fan blows air through the fill and sprayed
water to aid in the evaporation. Evaporation removes energy from the water dropping its temperature. The cooled water collects in the cooling towers basin
where it is pumped back into the chillers condenser and the cycle is repeated.
2.7.18 The AF-600 FP solution
With a frequency converter, the cooling towers fans can be controlled to the required speed to maintain the condenser water temperature. The frequency
converters can also be used to turn the fan on and off as needed.
Several features of the GE dedicated frequency converter, the HVAC frequency converter can be utilized to improve the performance of your cooling tower fans
application. As the cooling tower fans drop below a certain speed, the effect the fan has on cooling the water becomes small. Also, when utilizing a gear-box to
frequency control the tower fan, a minimum speed of 40-50% may be required.
The customer programmable minimum frequency setting is available to maintain this minimum frequency even as the feedback or speed reference calls for lower
speeds.
Also as a standard feature, you can program the frequency converter to enter a "sleep" mode and stop the fan until a higher speed is required. Additionally, some
cooling tower fans have undesireable frequencies that may cause vibrations. These frequencies can easily be avoided by programming the bypass frequency
ranges in the frequency converter.
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