If you manage a commercial building with a cooling tower, you’ve probably heard the term “drift” \u2014 but you may not realize how much it affects your water consumption, your chemical costs, and potentially your regulatory compliance. Cooling tower drift is a distinct phenomenon from evaporation, and understanding the difference matters for both your budget and your sewer credit applications.<\/p>\n
Evaporation is the cooling tower’s primary job \u2014 it removes heat by evaporating water into the atmosphere as pure water vapor. This is the intentional water loss that makes your cooling system work. Drift, by contrast, is the unintentional loss of water droplets that get carried out of the tower by the airflow. Unlike evaporation, drift droplets contain all the dissolved minerals and chemical treatments present in the circulating water.<\/p>\n
Think of it this way: evaporation is steam rising from a pot of boiling water. Drift is the tiny droplets that splash out of the pot when the boil is vigorous. Both result in water leaving the tower, but they carry very different things with them.<\/p>\n
The U.S. Department of Energy<\/a> notes that modern drift eliminators can reduce drift losses to 0.001 to 0.005 percent of the circulating water flow rate \u2014 a dramatic improvement over older tower designs that might lose 0.1 to 0.3 percent.<\/p>\n Drift matters for three reasons. First, it’s wasted water \u2014 and wasted treated water at that. Every droplet that drifts away carries expensive corrosion inhibitors, biocides, and scale control chemicals with it. Your chemical vendor has to compensate for these losses, which increases your treatment costs.<\/p>\n Second, drift can create regulatory issues. Because drift droplets contain biocides and other treatment chemicals, some municipalities have specific regulations about drift rates from cooling towers. The concern is primarily about Legionella bacteria \u2014 drift droplets can carry biological contaminants into the surrounding air, which is why proper tower maintenance and compliance programs<\/a> are essential.<\/p>\n Third, excessive drift can complicate your sewer credit calculations. Drift is technically water that leaves the tower but doesn’t go to the sewer \u2014 similar to evaporation. However, most utility credit programs focus on evaporation losses and may or may not include drift in their calculations. Understanding your tower’s drift rate helps you present accurate data in your sewer credit application<\/a>.<\/p>\n The most effective drift reduction technology is a drift eliminator \u2014 a component installed in the tower’s air discharge path that forces the airstream through a series of sharp turns. Water droplets, being heavier than air, can’t follow the turns and collect on the eliminator surfaces, draining back into the tower basin. Modern high-efficiency drift eliminators, typically made from PVC or polypropylene blade assemblies, achieve drift rates below 0.005 percent of circulating flow.<\/p>\n If your tower was built before 2000 and still has its original drift eliminators, upgrading to modern units is one of the most cost-effective improvements you can make. The water and chemical savings alone typically pay for the upgrade within 12 to 18 months. Beyond drift eliminators, maintaining proper water levels, keeping distribution nozzles aligned, and ensuring fans are operating at correct speeds all help minimize drift.<\/p>\nWhy Drift Matters<\/h2>\n
How to Reduce Drift<\/h2>\n