Water and wastewater consultant Paul Puckorius discusses water treatment modifications required by changing water quality.

Due to the use of reclaimed or recycled water, the quality of the concentrated cooling water in evaporative cooling systems is changing. Recycled water often contains higher levels of dissolved solids. Ammonia, nitrates, phosphate and organics also may be present. Some of these components such as nitrates and phosphate can be beneficial if levels are not too high. Most of the others, particularly ammonia, can be detrimental in several ways. For instance, ammonia attacks copper alloys and biological control chemicals. Ammonia also can serve as a nutrient, particularly with phosphate, increasing biological growth potential.

Even in cooling systems using city water, water quality is changing due to water conservation. Less water is discharged and more is recycled, resulting in an increase in dissolved solids. Additional water treatment often is required due to greater scaling, corrosion and biological problems.

Chiller Tube Design

Chiller tube design is changing, particularly the water side of the condenser section of the air conditioning machine. The use of enhanced copper tubes has increased the heat transfer efficiency over smooth tubes. Enhanced tubes are manufactured with lands and grooves along the inside wall, similar to those in the barrels of rifles. The design is a great improvement from the standpoint of heat transfer. However, for every action there is an equal and opposing reaction. There has been an increase in water-related corrosion and deposition in these enhanced tubes. This is particularly true when water flow is stagnant periodically. An increased and modified water treatment program usually is required to prevent both corrosion and deposition.

Even more improved heat transfer has been accomplished by the introduction of superenhanced copper tubes for the water side of the condenser. These tubes have fine, closely spaced lands and grooves and are similar in appearance to finned tubes on the refrigerant side of the condenser. Superenhanced tubes have an even greater tendency for corrosion and deposition than enhanced tubes. Specific startup procedures and continuing water treatment are needed to reduce damage and prevent premature failure of tubes.

Cooling Towers

Cooling towers also are improving in design, fabrication and operation. The use of high efficiency drift eliminators greatly reduces water loss. However, drift eliminators are prone to biological deposit buildup and plugging.

High efficiency cooling tower film fill is another great development, but it also has the potential for plugging from mineral and microbiological deposits. Again, improved water treatment programs are required to maintain clean film fill and efficient operation. New film fill with straight ports is less prone to microbiological deposits.

Metal cooling towers can provide long life due to galvanized steel construction. Often, metal cooling towers require modification of the water treatment program to prevent white rust. Program modification consists of utilization of specific water treatment chemicals and adjustment of water quality. Plastic and fiberglass cooling towers provide resistance to corrosion but may be subject to greater deposits. Changing technologies continue to improve cooling equipment operation and efficiency. Keep in mind that changing technologies also require modification of water treatment, operating procedure and awareness of potential problems.