Page 194 - WaterSense at Work

WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities
Cooling towers are used in a variety of commercial and institutional applications to
remove excess heat. They serve facilities of all sizes, such as office buildings, schools,
supermarkets, and large facilities, such as hospitals, office complexes, and university
campuses. Cooling towers dissipate heat from recirculating water that is used to cool
chillers, air conditioning equipment, or other process equipment. By design, they use
significant amounts of water.
Cooling towers often represent the largest use of water in institutional and commer-
cial applications, comprising 20 to 50 percent or more of a facility’s total water use.
However, facilities can save significant amounts of water by optimizing the operation
and maintenance of cooling tower systems.
Cooling towers work by circulating a stream
of water through systems that generate heat
as they function. To cool the systems, heat
is transferred from the systems to the water
stream. This warm water is then pumped
to the top of the cooling tower, where it is
sprayed or dripped through internal fill (i.e.,
a labyrinth-like packing with a large surface
area). Fans pull or push air through the tower
in a counterflow, crossflow, or parallel flow
to the falling water. As some of the water is
evaporated, the heat is removed.
The remain-
ing cooled water is recirculated back through
the systems to repeat the process.
The thermal efficiency and longevity of the
cooling tower and its associated water loops
depend upon the proper management of water recirculated through the tower.
Water leaves a cooling tower system in four ways: evaporation, blowdown or bleed-
off, drift, and leaks or overflows.
Evaporation is the primary function of the tower and is the method that transfers
heat from the cooling tower system to the environment. The quantity of evaporation
is not typically targeted for water-efficiency efforts because it controls the cooling
process, although improving the energy efficiency of the systems that use the cool-
ing water will reduce the evaporative load on the tower. The rate of evaporation from
Cooling Towers
North Carolina Department of Environment and Natural Resources, et al. May 2009.
Water Efficiency Manual for Commercial, Industrial and Institutional Facilities
Page 39.
Cooling towers