Page 200 - WaterSense at Work

October 2012
Retrofit Options
To improve the efficiency of an existing cooling tower, some retrofit options are
available, including: installing meters and control systems to help facility managers
monitor water use; improving the tower’s water quality to increase cycles of concen-
tration; using onsite alternative sources of water to replace potable make-up water;
and taking steps to reduce biological growth.
Installing Meters and Control Systems
When installing meters and control systems, consider the following:
To automatically control blowdown, install a conductivity controller, which can
continuously measure the conductivity of the cooling tower water and will initi-
ate blowdown only when the conductivity set point is exceeded. Working with
the water treatment vendor, determine the maximum cycles of concentration
that the cooling tower can sustain, then identify and program the conductivity
controller to the associated conductivity set point, typically measured in micro-
Siemens per centimeter (µS/cm), necessary to achieve that number of cycles.
Install automated chemical feed systems on large cooling tower systems (more
than 100 tons). The automated feed will monitor conductivity, control blow-
down, and add chemicals based on make-up water flow. These systems minimize
water and chemical use while protecting against scale, corrosion, and biological
If not already present, install flow meters on make-up and blowdown lines.
Meters can be installed on most cooling towers for less than $1,000.
Refer to the
previous “Operation, Maintenance, and User Education” section for recommenda-
tions on how to use the meters once they are installed.
Consider contacting the water utility to determine if the facility can receive a
sanitary sewer charge deduction from the potable water lost to evaporation. If
the utility agrees to provide this deduction, calculate the difference between the
city-supplied potable make-up water and the blowdown water that is discharged
to the sanitary sewer.
Improving Cooling Tower Water Quality
To improve the cooling tower water quality, consider the following:
To cleanse the cooling tower basin water and help the system operate more effi-
ciently, install a rapid sand filter or high-efficiency cartridge filter on a sidestream
taken from the cooling tower basin. This system will filter out sediments within
the basin water and return it to the cooling tower. This is especially helpful if the
cooling tower is subject to dusty conditions.
Install a water softening system on the make-up water line if hardness (e.g., cal-
cium and magnesium) limits the ability to increase cycles of concentration.
Cooling Towers