Cooling tower drift eliminators can sometimes take a back seat in many performance and maintenance plans.
We may tend to focus on components such as the gearbox, fans, fill media, or maintaining the water distribution
system. As we have discussed before, all of
your cooling tower parts are connected.
Therefore maintenance and care of some components over others can be just as harmful to your cooling tower performance. Drift eliminators
greatly affect your cooling tower water usage and capacity. Below we will dive into what drift eliminators are,
how they function, why they are so important in maximizing cooling tower water usage and much more.
What is a drift eliminator and how does it work?
Let's begin by defining "Drift." Drift is the circulating water that is lost from your cooling tower.
Drift is measured in % of the circulating water rate or % of GPM (Gallons per Minute). Thus, a drift eliminator
(or "DE" for short) is engineered and designed to retain the circulating water inside of the tower.
This happens by "capturing" the water droplets trapped within the exhaust airstream. These captured
water droplets then cascade as a very thin layer down the drift eliminator walls and back into the wet section of
your cooling tower, thus being re-introduced to the thermal process. This is how it works:
Many factors can affect the drift of your cooling tower such as:
- Air Velocity
- Water droplet size
- Seals
- Material Construction:
Most drift eliminators are constructed of a PVC (polyvinyl chloride) or PP (polypropylene) plastic. Each type of plastic composite can have a different surface energy affecting DE performance.
- Quality of DE panel installation
Now that we understand more about drift and how drift eliminators function, let's talk about the importance of
drift rate.
What does drift rate mean?
Drift rate within the cooling tower industry is defined as a percentage which is determined by how effective
the drift eliminator is at reducing drift. In today's industry the lowest possible drift rate is .0005%
however many DE's are manufactured at a .002% - .001% drift rate. This range, even though it allows for
greater drift loss, is an industry acceptable percentage. However the higher you accept your cooling tower
drift rate to be, the more you should understand how your drift rate impacts cooling tower capacity and water usage.
Why maintain the lowest possible drift rate?
- Reduces water loss and the need to introduce make up water. If less water is wasted then less water is being used therefore maintaining cooling tower capacity and reducing the need for make-up water.
- Reduces fan blade leading edge erosion
- Reduces other equipment erosion
- Reduces Legionella
- Reduces PM10 emissions
How can I calculate my drift rate?
At this point you may be curious to compare the difference of water lost between a .0005% drift rate and a .002% rate. In three steps you can calculate the water loss based on your drift eliminator's manufacturer determined drift rate. First, determine your entering water temp, exiting water temp, wet bulb temp, and circulating flow rate. For example these are some industry standards:
- Entering Water Temp: 95°F
- Exiting Water Temp: 85°F
- Site Wetbulb Temp: 78°F
- Circulating Flow Rate: 1,000 gpm
Second, take your (circulating flow rate) x (Drift rate/100) = Drift Loss (gal/m)
For example:
Drift Loss (gal/m) = 1000 gal/min x (0.0005/100) = 0.005 gal/min
Third, let's compare this to a drift rate of .002%. Using the above calculations, we would find
that there would be a drift loss of 1.2 gal/hr or a drift loss that is four times greater! That's a
lot of water to waste!
How can a drift rate of .0005% be maintained?
If you have recently purchased or have installed DE's with a .0005% drift rate,
how can you ensure that you have been maintaining this performance level? If you are not sure
these are some points to consider:
- Keep DE's free from blockage and debris by maintaining water quality. The quality of your cooling tower water is the main factor in drift eliminator maintenance (as well as fill media and nozzles).
- Maintain structural quality by checking for UV damage, cracking, clogging and the breakdown of the glue that holds the packs of drift eliminators together. Once pack glue breaks down, major drift loss occurs.
How do I know if I need to replace my DE's?
Complete a proper inspection to find out if your drift eliminators need to be replaced. During an inspection
your drift rate can be analyzed to determine if your DE's are maintaining performance. Furthermore a visual
indication of DE surface quality can be done to check color and durability. If your drift eliminators are grey in
color instead of black or are cracked, this suggests that UV damage is present causing your drift eliminators to
be brittle and leading to increased drift loss.
*UV damaged and brittle drift eliminator (left). Optimal condition drift eliminator (right)
.
Getting the highest quality drift eliminator with the lowest possible drift rate is important to your
cooling tower capacity and
water usage. So where do you turn to now? Search only the best drift eliminators
in the industry within
our online cooling tower parts warehouse or
give us a call for an expanded list of
DE brands and types to help you find the perfect drift eliminator technology for your cooling tower needs
and performance requirements.
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