Retrotec USACE - Manual (Page 203)

Appendix D D73
Figure D123. Example of the performance of
dirty cooling tower distribution nozzles.
If some of the nozzles are dirty, fl ow out of those nozzles is impeded and the
evenness of the water fl ow through the tower no longer takes place (Figure
D123). The cooling effectiveness is reduced, and the temperature of the leav-
ing water is warmer. Additional fan energy would be required to reduce the
water temperature to the desired value. This represents an energy waste that
could be avoided by cleaning the nozzles.
D.4.2.18 Cooling Tower Leaks and Excessive Blowdown
(Ineffi ciency)
Cooling towers evaporate water for cooling, and thus the concentration of
salts and other impurities increases. To maintain these concentrations within
acceptable levels, some of the cooling tower water is drained away from the
system. This is called “blowdown.” If too much blowdown occurs, pumping
energy is wasted by not returning this extra water to the system. Chemicals that
are added to this water are also wasted. The same can be said about leaks that
occur in the cooling tower basin and the housing that surrounds the fi ll.
D.4.2.19 Imbalance of Flow over Cooling Towers (Ineffi ciency)
A cooling tower is a heat exchange device where water is cooled by passing air
through it, providing for evaporation. The evaporation of some of the water re-
moves heat and cools the rest of the water. In a cooling tower, water is pumped
to the top of the tower, where it enters a piping header system. There are open-
ings in these headers where nozzles are placed to provide a spray pattern to
the downward-fl owing water. This distributes small droplets of water properly
across the fi ll section of the tower. Here a number of closely spaced vertical
panels are placed so the water can fl ow over them as it drops downward. The
fi ll section slows the progress of the fl owing water and provides time for water
evaporation. Several fi ll sections may be needed to obtain the desired cool-
ing of the water. The cooling of the water can be increased by moving more
air through the cooling tower, and there are fans placed in the tower for this
reason. Normally the fans are variable fl ow or have variable pitched blades to
obtain the correct air fl ow from the desired water cooling.