Page 190 - Industrial Ventilation Design Guidebook

152 CHAPTER 4 PHYSICAL FUNDAMENTALS

4.4.3 Cooling Water Systems
Cooling water systems used for process heat rejection can be classified under
one of the following headings:
• Open recirculation
• Closed recirculation
• Once-through system

4.4.3.1 Open Recirculation
Open recirculation includes the standard cooling tower, spray pond, or
evaporator condenser as shown in Fig. 4.39. An arrangement of this type pro-
vides an efficient cooling system. Its main disadvantage is growth of microor-
ganisms such as the Legionella species. To protect people from these bugs, the
biological water treatment represents a very high cost in the operation of the
plant. This arrangement is losing favor with many engineers and is being re-
placed by the less efficient closed systems.
Typical applications include heat rejection from the refrigeration plant. The
highest proportion of cooling takes place by evaporation.
Advantages

1. Can cool water down to 2 °C above the wet bulb temperature

FIGURE 4.39 Cooling water system (open recirculation).