Cooling Tower

cooling tower box type

cooling tower box type

Cooling towers are used in central air conditioning systems. The function of the cooling tower is to cool the warm water from the chiller condenser. Following the central air conditioning system cycle, the heat from the rooms in a building is transferred to chilled water, which is then transferred into the refrigerant, and finally to the cooling water. The cooling tower is at the final point of the heat transfer. The heat is transferred to the atmosphere.

cooling tower fan

cooling tower fan

The heat in the cooling water is removed by letting moving air come into contact with it. Water is normally spread out and allowed to drop down by gravity from a height. Plastic fillings are arranged so as to increase the wetted surface of the water while it is dropping, while at the same time provide better contact between the air passages and the water.

There are basically 2 types of designs:

  • Cross Flow
  • Counter Flow

Cross Flow

As the name suggests, the flow of water is at right angles to the flow of air. The cooling tower for this type of design is usually shaped like a box. Warm water is pumped to the top of the cooling tower where it is distributed to the sides and allowed to drop through small holes. Plastic air intake louvers at the sides of the cooling tower allow the water to spread out while dropping. Air from the outside is sucked into the cooling tower by several fans located at the top. The incoming air comes into contact with the dropping water, and the latter is cooled. The cooled water is collected at the bottom of cooling tower. This water is then pumped out again and circulated through the chiller. The heat from the chiller is transferred to it again. The warm water then returns back to the top of the cooling tower and the cycle starts again.

Counter Flow

cooling tower bottle type

cooling tower bottle type

Counter flow cooling towers have the air passage flowing directly against the flow of the water. As with the cross flow design, water is allowed to spread out with the help of air inlet louvers. Their bottle like shape characterizes this type of cooling towers. There is only one single fan at the center. Fitted below the fan is a rotating water pipe distributor. The pipes of the water distributor shoots water only from one side. The action of the water pressure shooting from one side rotates the distributor. The water is thus dropped evenly over the air inlet louvers. The water dropping by gravity meets head on with the up moving air current sucked in by the fan. The air cools the water. The water collected at the bottom of the cooling tower is pumped to the chiller, becomes heated up again, and is then returned back to the cooling tower for cooling.

Water Treatment

In cooling towers, the cooling effect is achieved by evaporation of a portion of the water passing through it. As the water is evaporated, impurities remain in the recirculating water. The concentration of the dissolved solids increases rapidly and can reach unacceptable levels. In addition, airborne impurities are often introduced into the water. If the contaminants are not controlled, they can cause scaling, corrosion, and sludge accumulations which can reduce heat transfer efficiencies.

In order to control the concentrations, it is necessary to bleed a small amount of circulating water from the system and top up with fresh water. If the site conditions are such that constant bleed-off will not control scale or corrosion, chemical treatment is necessary. Even with bleed-off or chemical treatment, it is still necessary to control biological contamination. The growth of algae, and other microorganisms can reduce system efficiency and may even contribute to potentially health hazards. Biocides are used to treat the water to control the biological growths.