Specifications

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.
Cooling towers cool the condenser water by evaporation.
The condenser water is sprayed into the cooling tower
onto the 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
basin of the cooling tower where it is pumped back into
the chiller condenser and the cycle is repeated.
2.7.18 The VLT Solution
With a frequency converter, the cooling tower 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.
With the Danfoss HVAC frequency converter, as the cooling
tower fans drop below a certain speed, the cooling effect
decreases. When using a gear-box to frequency control the
tower fan, a minimum speed of 40–50% could 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.
The frequency converter can be programmed to enter a
“sleep” mode and stop the fan until a higher speed is
required. Additionally, some cooling tower fans have
undesirable frequencies that can cause vibrations. These
frequencies can easily be avoided by programming the
bypass frequency ranges in the frequency converter.
Frequency
converter
Water Inlet
Water Outlet
CHILLER
Temperature
Sensor
BASIN
Conderser
Water pump
Supply
130BB453.10
Illustration 2.13 Frequency Converters Used with a Cooling Tower Fan
Introduction VLT® HVAC Drive FC 102 Design Guide
26 MG16C102 - Rev. 2013-08-20
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