P r essur e
sig nal
C ooling c oil
Hea ting c oil
D1
D2
D3
F ilt er
P r essur e
tr ansmitt er
Supply fan
R etur n fan
T emper a tur e
sig nal
T emper a tur e
tr ansmitt er
e3
0b
b4
51
.1
0
Drive
Drive
Illustration 12: Constant Air Volume
3.1.2.3 Cooling Tower Fan
Cooling tower fans 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.
They cool the condenser water by evaporation. The condenser water is sprayed into the cooling tower until 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.
The VLT Solution
With a drive, the cooling towers fans can be controlled to the required speed to maintain the condenser-water temperature. The
drives can also be used to turn the fan on and off as needed.
Several features of the Danfoss dedicated drive can be utilized to improve the performance of cooling tower fans applications. 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
gearbox to frequency control the tower fan, a minimum speed of 40–50% is 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, the drive 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 may cause vibrations. These frequencies can easily be avoi-
ded by programming the bypass frequency ranges in the drive.
AJ363928382091en-000101 / 130R0983
22 | Danfoss A/S © 2021.04
Product Overview
VLT® Flow Drive FC 111
Design Guide