UFC 3-240-13FN
25 May 2005
CHAPTER 4
COOLING WATER SYSTEMS
4-1
TYPES OF COOLING WATER SYSTEMS. Cooling water systems
remove heat generated from a variety of industrial processes. There are three basic
types of cooling water systems: once-through, open recirculating, and closed
recirculating cooling water systems. This Chapter describes once-through and open
recirculating systems. Chapter 5 describes the closed recirculating system.
4-1.1
Once-Through Cooling Water Systems. Once-through cooling water
systems use cool water that circulates only once through the entire system before being
discharged. This type of system is commonly found along rivers or coastlines where
abundant water is available for use. The system contains heat exchange equipment and
transfer piping, as shown in Figure 4-1. Power utility services often use this type of
system.
Figure 4-1. Once-Through Cooling Water System Diagram
Pump
Discharge
Intake
Cool Water
Warm
Water
Heat
4-1.2
Open Recirculating Cooling Water Systems. Open recirculating cooling
water systems are open to the atmosphere and continuously recycle and reuse the
cooling water. These systems are composed of an evaporator unit, a cooling tower, or
an evaporative condenser. These units mix air and water and allow some of the water to
evaporate, cooling the balance of the water volume. The cooled water is then circulated
to heat exchangers or chillers, where heat is added to the cooling water thereby
removing heat from the process flow stream. The warmed water is then circulated to
the cooling tower, where the cycle is repeated. Water is lost from the system primarily
through evaporation; however, a portion of the cooling water must be discharged as
waste (i.e., blowdown) to maintain a suitable water quality within the system. All water
lost from the system is replaced by makeup water. Recirculating cooling water systems
are found in most air conditioning chiller operations, as well as many heat exchange
operations. Evaporative fluid coolers and evaporative condensers are terms defining
open recirculating cooling water systems that use evaporators, which are slightly
different than a cooling tower and do not send the cooled water out of the evaporative
unit itself. An evaporative cooler cools a circulating fluid that does not change phase
(e.g., does not condense from a gas to a liquid). An evaporative condenser cools a
circulating fluid from a gas into a liquid, such as a refrigerant. The hot fluid that is to be
cooled is brought to the unit. Figure 4-2 shows a typical evaporative cooler and
evaporative condenser diagram; Figure 4-3 shows a typical open recirculating cooling
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