Water Treatment Matters Series
By John Caloritis
Technical Director at Metro Group
Certified Water Technologist Board of Directors, Association of Water Technologies
Maintaining pH in a Cooling Tower
We are often asked about the importance of the pH measurement in open HVAC systems, and the types of control strategies that may be needed to regulate pH. Cooling towers specifically fall into this category. Modern evaporative systems (towers, fluid coolers, evaporative condensers) are operated at elevated cycles of concentration to minimize the amount of required bleed/discharge water. Doing so is a sustainable and money saving practice. However, this cannot be done in a vacuum or without scientific consideration.
Cycles Management: We must start with the recognition that all cooling water treatment programs are limited by the chemistry of the makeup water. Geographies where “lean” water is present, can often cycle 10 to 12 times the makeup without trouble, and those with harder water supplies may only be able to reach perhaps 3 to 5 times. Regardless, the water treatment industry is regularly operating cooling water pH levels that reach 9.0 or above, with many routinely falling into the range of 8.0 to 9.0.
Decisions to Regulate Cycles: Are primarily made based upon the heat exchange conditions faced, along with system metallurgy. The water treatment professional lands on a suitable rate of bleed to be maintained, based on the concentration of other water parameters first, with attention to pH being a secondary but affected consideration. High pH towers can be corrosive to certain metals, and elevated pH in the presence of high temperatures and over saturated minerals will cause precipitation and mineral deposition.
3 pH Control Strategies
1. System bleed off – The regulated amount of bleed is achieved via automated controllers that read conductivity, open a solenoid bleed/drain valve, and through dilution with fresh water, allow desired levels to be maintained. Bleed-off can also be managed manually, but this practice requires far more attention and more frequent testing. Controlling bleed to control cycles, indirectly fixes pH to a known level.
2. Acid Feed – Where scale formation is a worry and additional cycles are needed for economic reasons, it sometimes becomes important to directly control pH. So in water supplies where alkalinity is a limiting factor, the industry will utilize “acid feed” and “pH control” to destroy cycled alkalinity by injecting sulfuric (or other) acids proportionally. This is a direct strategy which helps cooling tower owners conserve water without sacrificing performance.
3. Water Softening – This is typically not an economically feasible strategy, but certainly one that is also used to help build cycles (and reduce bleed) where the amount of hardness in the cycled water can cause mineral deposition. It is another indirect strategy to manage deposit potential, and in the process fix pH to a known level.
Understanding your Water Chemistry
In summary, pH is an important value to know about when managing cooling water chemistry. But it alone is not always a directly targeted control variable. Rather, by understanding the water chemistry being applied, the professional water treater will determine the cycles of concentration that are needed to achieve proper balance and work with the pH value upon reaching design cycles of concentration. When seeking support with your water treatment needs, look to the Metro Group, Inc., or AWT partners in your geography. And always think about the CWT (Certified Water Treatment) professional with confidence.
Questions about maintaining your cooling tower? Ask John!
Do you have more questions about maintaining pH in cooling towers or other Water Treatment Matters? Please let us know by filling out our contact form and we’ll get back to you! Ready to start planning your cooling tower maintenance program? Metro Group offers New York’s only fully turn-key Cooling Tower Compliance Program and is committed to keeping residents safe using the most advanced chemical treatment programs and equipment. Contact us for a quote!