Danfoss VLT Series Design Manual page 24

2. Introduction to VLT HVAC Drive
2.7.16. 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
2
efficient than air cooled chillers. Depending on climate, cooling towers are often the most energy
efficient method of cooling the condenser water from chillers.
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 evapo-
ration. 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.
2.7.17. The VLT 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 Danfoss HVAC dedicated drive, the VLT HVAC Drive 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 unde-
sireable 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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Water Inlet
BASIN
MG.11.B2.02 - VLT
Temperature
Sensor
Conderser
Water Outlet
Water pump
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is a registered Danfoss trademark
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VLT HVAC Drive Design Guide
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