Choosing The Right Fill Based On Water Quality

Brentwood often gets emails for a situation that goes something like, “Here is a report showing the water for my cooling tower. What fill should I use?” That’s a good question to ask, although answering it at times can be a little challenging. From the aspect of trying to maximize the lifetime of your investment in fill, it is important to choose a fill that is appropriate for the quality of the water that will be flowing through it. The difficulty often lies in getting the information that applies to the fill, as opposed to data that applies to other parts of the cooling system in the facility, within which the cooling tower is a small (and often undervalued), part. How does this relate to water quality?  Let’s look at an example: Water quality analysis report.

As you can see in this example report, there are two pages of information related to what appears to be water sourced from a well. Surely in two pages of data we’ll have information that sheds light on which fill might be suitable for that water… Right?? Unfortunately, the answer is, “No.” The results on the two pages are mainly lists of constituent cations and anions –metals and salts, with a few other items thrown in.

The question that this now begs is: If this isn’t the information needed to select a fill, what is? The short answer is: Things that could build up and plug or clog the fill. Those things are: Scale, sediment, and debris in the water; biological growth; and finally, the things that would help adhere those other items to the fill, such as biological organisms and oils & greases.

Scale is the minerals that result from the dissolved solids (TDS = Total Dissolved Solids) that no longer stay in solution in the circulating water. This is information that is critical to the water treatment program since it is up to the water treatment program to keep the dissolved solids in solution. As long as these minerals/salts stay dissolved, they are not a factor in fill selection. It is only in extreme situations where the level of difficulty at keeping TDS dissolved is very great that scale potential can potentially come into play with fill selection. No fill is designed to be scale free, however, some fills may be more tolerant of scale formation and exhibit less impact from scale formation than others.

The main factors that are needed to make an informed fill selection relate to Total Suspended Solids (TSS), biological population levels, and oils/greases. The general term for the impact of these factors is “fouling,” and it relates to matter that is disparate from the water that could become deposited on the fill and cause it to plug. The TSS value shows the amount of actual solid matter that is available to become lodged in the fill, and the biological population levels and oils/greases indicate the amount of “sticky” constituents that would make the TSS materials stick to the fill. Previous studies have shown that high TSS levels in and of themselves do not equate to fouling issues. The solids require something to retain them in the fill. The natural excretions of biofilm populations and oils/greases provide the “glue” to hold the TSS in the fill.

Remember the example water analysis report? Why weren’t TSS, biological population counts, and oil/grease levels listed? The main reason is that the test methods for those items take time and additional effort – above and beyond simple chemical analysis that can be done  by putting a sample of water into a machine. Because of this, you must specifically request these tests if you want to help guide proper fill selection.

Brentwood has multiple informational documents related to water quality and fill selection. This is a very complex topic, and the information presented here is a small look into the process. Please reach out to Brentwood’s Cooling Tower Team with any questions you might have for your projects. With the right information and the proper marriage of your fill with the water & water treatment program used with your cooling tower, you can ensure that you will keep getting the coldest water for the longest time from your fill.