Cooling towers

Electrical Energy Equipment: Cooling Towers

COOLING TOWERS
1. INTRODUCTION...........................................................................................1 2. TYPES OF COOLING TOWERS ................................................................4 3. ASSESSMENT OF COOLING TOWERS ..................................................7 4. ENERGY EFFICIENCY OPPORTUNITIES.............................................9 5. OPTION CHECKLIST ................................................................................14 6. WORKSHEETS ............................................................................................15 7. REFERENCES..............................................................................................17 1. INTRODUCTION
This section briefly describesthe main features of cooling towers.

1.1 What is a cooling tower?
Cooled water is needed for, for example, air conditioners, manufacturing processes or power generation. A cooling tower is an equipment used to reduce the temperature of a water stream by extracting heat from water and emitting it to the atmosphere. Cooling towers make use of evaporation whereby some of the water is evaporatedinto a moving air stream and subsequently discharged into the atmosphere. As a result, the remainder of the water is cooled down significantly (Figure 1). Cooling towers are able to lower the water temperatures more than devices that use only air to reject heat, like the radiator in a car, and are therefore more cost-effective and energy efficient.

Figure 1. Schematic diagram of a cooling watersystem (Pacific Northwest National Laboratory, 2001)

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Electrical Energy Equipment: Cooling Towers

1.2 Components of a cooling tower
The basic components of a cooling tower include the frame and casing, fill, cold-water basin, drift eliminators, air inlet, louvers, nozzles and fans. These aredescribed below.1 Frame and casing. Most towers have structural frames that support the exterior enclosures (casings), motors, fans, and other components. With some smaller designs, such as some glass fiber units, the casing may essentially be the frame. Fill. Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximizing water and air contact. There are two types of fill:Splash fill: water falls over successive layers of horizontal splash bars, continuously breaking into smaller droplets, while also wetting the fill surface. Plastic splash fills promote better heat transfer than wood splash fills. Film fill: consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in contact with the air. These surfaces may be flat,corrugated, honeycombed, or other patterns. The film type of fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill. Cold-water basin. The cold-water basin is located at or near the bottom of the tower, and it receives the cooled water that flows down through the tower and fill. The basin usually has a sump or low point for the cold-water dischargeconnection. In many tower designs, the coldwater basin is beneath the entire fill. In some forced draft counter flow design, however, the water at the bottom of the fill is channeled to a perimeter trough that functions as the coldwater basin. Propeller fans are mounted beneath the fill to blow the air up through the tower. With this design, the tower is mounted on legs, providing easy access to the fansand their motors. Drift eliminators. These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere. Air inlet. This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower (cross-flow design) or be located low on the side or the bottom of the tower (counter-flow design). Louvers. Generally, cross-flow towers...