Understanding Drift Loss & Evaporation Loss: Strategies to Minimise Them for Maximum Efficiency

In the world of cooling towers, the two main types of ‘water loss’ are Evaporation Loss and Drift Loss. Understanding the differences between the two, their causes, and how to minimise them is key to optimising your factory's water efficiency and operating costs.

1. Evaporation Loss

• What is it?

• Evaporation Loss is water that changes from a liquid phase to water vapour as part of the core cooling process itself. The evaporation process requires heat energy (latent heat), and this energy is taken from the remaining water, making it cooler.

• Why does this happen?

• Evaporation loss is a fundamental and intentional process in the working principle of cooling towers. Without evaporation, there would be no cooling. This is not a loss that can be eliminated, but rather the water consumption necessary to cool the system.

• How to Minimise It?Since this is central to the process, all we can do is manage it efficiently:

  • Load Optimisation: Ensure that the cooling tower is not operating beyond its required capacity.

  • Concentration Cycle Control: By increasing the concentration cycle (through controlled blowdown), the amount of water evaporated to cool the same volume of water becomes more efficient.

  • Use of Quality Cooling Water: Water with low hardness will allow for a higher concentration cycle, reducing the volume of makeup water required.

2. Drift Loss (Water Loss Due to Wind Drift)

• What is it?

• Drift loss is liquid water droplets carried by airflow out of the cooling tower before they have time to evaporate. This is different from water vapour (steam), which is the result of evaporation.

• Why Does It Occur?

• Drift loss occurs due to the high-speed contact between air and water. Although undesirable, this phenomenon is very difficult to avoid 100% in any mechanical system. However, the amount can and should be significantly reduced.

Solutions to Minimise Drift and Evaporation Loss

How to Minimise Drift Loss (Most Important):

1. Installation of an Efficient Drift Eliminator:

   • This is the most effective solution. A drift eliminator is a special structure (usually made of PVC) installed at the air outlet of the cooling tower.

   • How it works: They create a winding path that forces water droplets to hit their surface, clump together, and eventually fall back into the basin, while air can pass through.

   • Eliminator quality: High-quality drift eliminators from BHL can reduce drift loss to 0.001% or less of the water circulation rate, well below industry standards.

2. Fan Speed Optimisation:

   • Excessive fan speed is not only energy-intensive but also increases air velocity, which can carry more water droplets. The use of a Variable Speed Drive (VSD) helps regulate fan speed according to the required load.

How to Manage Evaporation Loss (For Maximum Efficiency):

1. Automatic Blowdown Controller & Water Treatment:

   • By controlling the concentration cycle through automatic blowdown, you ensure that every drop of evaporated water is used to cool water with optimal mineral concentration, thereby reducing overall makeup water requirements.

2. Use of Flow Meters and Monitoring Systems:

   • Install flow meters on the makeup water and blowdown lines. This data helps you monitor water consumption patterns, detect anomalies (such as leaks), and continuously improve system efficiency.

Conclusion: Losses Exist, but They Can Be Managed

• Evaporation loss is the lifeblood of the cooling process and must be managed with smart water treatment.

• Drift Loss is waste that can and must be aggressively minimised with the right technology.

Investing in high-quality drift eliminators and automatic blowdown systems will quickly pay for itself through:

• Savings on water and chemical treatment costs.

• Protection of the environment and assets around the cooling tower.

• More efficient and controlled system performance.