Key Terms in Cooling Tower Systems

Understanding the operational language of cooling towers is key to the efficiency and longevity of your cooling system.

Operational Terms & Performance Calculations

1. Make-Up Water

   • Definition: Additional water supplied to replace water lost due to Evaporation Loss, Drift Loss, and Blowdown.

2. Evaporation Loss

   • Definition: The volume of water lost due to evaporation when cooling hot water. This is the main cause of water loss and mineral concentration.

3. Drift Loss

   • Definition: A small amount of water carried by airflow out of the cooling tower in the form of droplets, not vapour.

4. Windage Loss

   • Definition: Another term often equated with Drift Loss, which is the loss of water carried away by the wind.

5. Bleed-Off / Blowdown (Concentrate Disposal)

   • Definition: The process of discharging a portion of concentrated circulating water to control the level of mineral and impurity concentration.

6. Automatic Blowdown

   • Definition: A system that automatically discharges water based on real-time TDS readings, ensuring optimal water and chemical efficiency.

7. Cycle Of Concentration (COC)

   • Definition: The ratio between the mineral level in the circulating water and the minerals in the make-up water. A high COC saves water but increases the risk of scaling.

8. Delta T (ΔT / Temperature Difference In-Out)

   • Definition: The temperature difference between the hot water entering and the cold water leaving the cooling tower. An optimal ΔT indicates good heat exchange performance.

9. Approach (Temperature Approach)

   • Definition: The temperature difference between the cold water leaving the cooling tower and the wet-bulb temperature of the surrounding air. The smaller the value, the more efficient the cooling tower.

Water Condition & Quality Terms

1. pH

   • Definition: The level of acidity or alkalinity of water. Low pH causes corrosion, high pH triggers scaling.

2. TDS (Total Dissolved Solids)

   • Definition: The total concentration of all minerals and salts dissolved in water. The main parameter for controlling COC and blowdown.

3. Total Alkalinity

   • Definition: The capacity of water to neutralise acids. High alkalinity greatly affects the potential for scaling.

4. Hardness

   • Definition: The concentration of calcium (Ca) and magnesium (Mg) ions in water. The main cause of scale formation.

5. TSS (Total Suspended Solids)

   • Definition: Solid particles (such as mud, dust) suspended in water, which can clog nozzles and fill packings.

6. Turbidity

   • Definition: The level of water turbidity caused by TSS, which reduces heat transfer and cleaning efficiency.

7. PPM (Parts Per Million)

   • Definition: A unit of measurement commonly used for water parameter concentrations such as TDS, Hardness, etc. (1 ppm = 1 mg/L).

Problem & Control Terms

1. Scaling

   • Definition: Hard deposits (usually calcium carbonate) that adhere to pipe surfaces and fill packing, inhibiting flow and heat transfer.

2. Corrosion

   • Definition: The process of metal deterioration (such as pipes and tower structures) due to chemical or electrochemical reactions with the environment.

3. RSI (Ryznar Stability Index)

   • Definition: An index to predict the tendency of water to form scale or be corrosive. A balanced value (6-7) is desirable.

4. LSI (Langelier Saturation Index)

   • Definition: Another index to assess water stability. Positive values = tendency to scale, negative values = tendency to corrode.

5. Biofilm (Bioproliferation)

   • Definition: A slimy layer formed from colonies of microorganisms (bacteria, algae, fungi) on the surface of the system, which can reduce efficiency and cause Legionella.

6. Fouling (scale sludge)

   • Definition: The accumulation of scale, sludge and other debris. If left unchecked, it will cause problems in the cooling tower.