Cooling Tower Fan - Danfoss VLT Series Design Manual

2. Introduction to the VLT HVAC Drive

2.6.16. 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
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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 tower's "fill" to increase
its surface area. The tower fan blows air through the fill and sprays water to aid in the evaporation.
Evaporation removes energy from the water, thus dropping its temperature. The cooled water
collects in the cooling towers basin, where it is pumped back into the chiller's condenser, and the
cycle is then repeated.
2.6.17. The VLT solution
With an adjustable frequency drive, the cooling towers fans can be set to the speed required to
maintain the condenser water temperature. The adjustable frequency drives can also be used to
turn the fan on and off as needed.
Several features of the Danfoss HVAC dedicated drive, the VLT HVAC Drive can be utilized to
improve the performance of your cooling tower fan application. As the cooling tower fans drop
below a certain speed, the effect the fan has on cooling the water becomes insignificant. 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.
Another standard feature is the "sleep" mode, which allows the user to program the adjustable
frequency drive to stop the fan until a higher speed is required. Additionally, some cooling tower
fans have undesirable frequencies that may cause vibrations. These frequencies can easily be
avoided by programming the bypass frequency ranges in the adjustable frequency drive.
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Water Inlet
BASIN
Water Outlet
MG.11.B4.22 - VLT ®
VLT
Temperature
Sensor
Conderser
Water pump
is a registered Danfoss trademark.
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