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Cooling Tower Efficiency with Water Resources for Practical Business Application
Ryan Barber, Stationary Engineer
May 2014
The purpose of this paper is determining the facts of reclaimed/ recycled water on a
current cooling tower application and introducing a new water softener system. While no
documented information discussing no chemicals for biological growth or corrosion with ZBD
has been determined, the research did discuss white rust corrosion and the technology preventing
and causing such lasting effects. In the Stationary Engineering field, little detailed information is
available for water chemistry. Water chemists are the first to answer the technical questions
about using zero blow down technology. Caution should be granted to implementing a system
before through research into the technology is being proposed. Increasing the pH also increases
corrosion to copper and galvanizing associated with cooling towers. Should a softener system be
introduced, monitoring copper and galvanizing coupons have been highly recommended based
on the research data. Using some chemicals preventing corrosion to metal surfaces was not
obtained from the research.
The business of the Stationary Engineering field is sustaining the energy and resources
necessary for building operations. We are responsible for the operation, maintenance, and repair
of industrial, commercial, and chemical plants. Engineers achieve this task by saving water and
increasing the cycles of concentration in cooling towers. Businesses will save the annual cost of
maintaining the system and energy efficiency with less chemicals purchased and labor; the only
down side could be the large capital investment in a system with potential long term repairs to
the metals affected by untreated water. The human eye may not see interior corrosion on metal
surfaces for several years into the operation resulting in catastrophic losses in capital
investments. Understanding the tradeoff between water efficiency compared to chemical usage is
the focus of this paper.
Cooling tower systems are increasingly becoming part of the new energy efficiency
recommendations to allow an increase in cycles of concentration for better business practices and
environmental concerns. Cycles of concentration are calculated by dividing the dissolved solids
level in the cooling tower water by that of the makeup water. After cooling tower water
evaporates, magnesium and calcium are left within the tower forming scale and biological
growth. Facilities today are using municipal water treatment plants reclaimed/recycled water for
irrigation and large, not potable, water resources. The recycled water from treatment plants
contain high levels of ammonia not completely removed from human body waste. Phosphates
from household soaps and detergents increase the TDS (Total Dissolved Solids) residuals in
water from treatment plants. Treating the reclaimed/ recycled make up water increases the
cooling tower water corrosion chemical program and biological treatment requiring owners to
use chemicals or other methods of non chemical means treating the water for bio-growth and
corrosion. By determining the incoming make up water chemistry levels and the cooling tower
cycles of concentration, businesses can reduce their water blown down to the sewage drain
system by using a zero blow down technology.

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During the cooling towers first several months in new operation, corrosion can occur if
the water pH levels are not within a tolerance of 7.0 – 8.2. For proper passivation to occur and
prevent the start of galvanizing corrosion called white rust, the tower water must be treated
properly (BAC technical resources). Higher alkaline (pH) chemistries actually inhibit the
formation of protective films on the galvanized surfaces inside of cooling towers allowing the
growth of white rust. Baltimore Air Coil Company technical bulletin states soft water (less than
30 ppm total hardness) combined with high pH (over 9.0) can increase white rust in cooling
towers. If the makeup water source is soften by mechanical means, white rust could be
prevented. Coating the cooling tower galvanized steel surfaces with a hybrid polymer and Tri
Armor Corrosion Protection System would help prevent white rust. Baltimore Air Coil Company
can provide more recommendations on their products. They recommend a competent water
treatment specialist be consulted during the initial system operation. If an existing cooling tower
has moderate to severe white rust, the material will have to be cautiously cleaned with a soft
bristle brush and not wire wheel or heavy tools to prevent the galvanizing from further damage.
Reducing the M alkalinity from makeup reclaimed/ recycled water removes the natural
passivating process which creates carbonate and bicarbonate alkalinity on steel (Harfst, W.
2009). Maintaining the towers at 8.5 pH or higher creates an environment eliminating
galvanizing steel protection.
Cooling tower water systems using soft water technology have different risks and
precautions before starting a new tower system. The soften water mixed with existing evaporated
cooling tower water is a high mix of brine and silica treated water. Given the higher sodium
content of soft water, corrosion (white rust) can form if prevention measures are not adhered to
properly. In 2007, the Water Conservation Technology International (WTCI) unit installed a
water softener system in a Seattle, Washington facility. The cooling towers were all fiberglass
but they installed coupon racks measuring the occasional corrosion. There concern is copper and
zinc corrosion. The higher TDS keeps bacteria from growing; addressing the user’s biological
growth concerns (Washington State Department of Ecology, 2007). The departments Technical
Resources for Engineering Efficiency surveyed four sites in the greater Washington State areas.
Corrosion is a concern for copper systems from the tower water. They are monitoring their
coupon samples every 90 days for corrosion after startup of the cooling towers.
Calcium and magnesium are natural corrosion inhibitors for cooling tower systems. The
importance of maintaining a corrosion management program is important in controlling the
proper pH and TDS levels. An ion system (soft water) removes much of the magnesium and
calcium from makeup water. Maintaining the proper levels is essential for cooling water
chemistry. Silica chemistry can provide a significant greater corrosion protection with high TDS.
Silica chemistry alone is not effective in corrosive attack of copper by ammonia (Walters, J.,
Duke, D.). Silica can prevent mild steel, copper, stainless steel, aluminum, zinc, and galvanized
steel exposed to high evaporative concentrations of corrosive ions contained in a ZBD (zero
blow down) operation. ZBD chemistry naturally controls tower water greater than pH 9 (Walters,
J., Duke, D.). The chemistry causes ammonia ion residuals to be reduced with lower ranges.
When systems operate at high TDS and high pH (over 9) corrosion of aluminum and zinc metals
are vulnerable. Measures for operating the ZBD system should be reviewed with California Title
22 requirements. Conserving water loss by fewer blows down and increasing the cycles of
concentration is the sustainability goal. With the current water drought in 2014 many businesses

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are required by water municipal agencies to reduce water usage by over 25%. The new focus is
non chemical programs.
If using non chemical programs or increasing the chemistry of potable or non potable
water you can also increase the efficiency of your cooling tower performance. Gaining 10 cycles
of concentration is difficult unless your system is ZBD. Maintaining the system hardness of 350
– 400 ppm is a general tolerance for safe corrosion levels. Once the cooling tower has been
operation for over 90 days, the risk of white rust is reduced from natural silica and magnesium in
potable or non potable makeup water and introduced water chemistry. A high Total Dissolved
Solids and pH level prevents bacteriological growth eliminating the need for chemical bio-
growth chemical means. In traditional chemical systems using two different biocides is more
effective with dispersing growth issues. If systems use softened water for makeup the chemistry
will have to be reviewed for corrosion protective materials. Introducing soften make up water to
the cooling tower has some inherit risks. The salt used to make brine will need to be monitored
by site engineers. Transportation of the salt for delivery to the site, storage, and loaded in brine
tanks needs to be considered for safety and corrosion. Softener systems will regenerate the ion
beads within the containers on a regular basis, depending on makeup water chemistry. Each re-
generation will remove brine form the storage tanks to softener cylinders regenerating the ion
beads. The excess salt is flushed down the municipal sewer system. The amount of regeneration
is dependent on the initial make up water chemistry. Some systems may regenerate every 20
minutes flushing an estimated 10 gallons of brine water down the sewage drain. The local
municipal waste water facility should be contacted on the allowable amount of brine entering
their raw sewage system.
Makeup water softening is gaining popularity within the United States. As we shorten our
annual rain fall, our natural resources are being diminished. Municipal water programs are using
reclaim/ recycled water for large non human water resources such as cooling towers. Scale can
be eliminated completely by obtaining higher cycles with ZBD from softener systems. Cycles of
concentration above six requires a bypass filter preventing deposition problems (Keister, T.
2008). Controlling the current cooling tower galvanized metals from white rust requires specific
inhibitor technology. Timothy Keister, Cooling Water Management- Basic Principles and
Technology highly suggest using a water management firm with a strong background in soft
water technology. Many systems are on the market to reduce scale build up. Introducing water
softener programs to copper and galvanizing without monitoring for corrosion can be costly.
Businesses with ISO 9001:2008 certification is one source of a preferred water chemistry
organization. A water treatment specialist with expertise in water chemistry, water softening, and
cooling tower mechanicals are the best suited for modifying or consulting on new installations.
Non chemical programs and technology has existed for many years. Finding a reputable,
local chemical treatment company will require research in their education, clients, and
technology. New technology is being introduced with fair results. Reverse osmosis systems, Ion
(softener) systems, and acid induced methods are currently on the market. Determining the
proper system for the current application will require some research. Corrosion is more
damaging to metal surfaces (galvanized, zinc, copper, and aluminum metals) than bio-growth.
Bio-growth will diminish the cooling tower energy efficiency but corrosion will reduce the life
expectancy of the equipment.

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References:
Conserve Water by Improving Cooling Tower Efficiency. 2009. William Harfst. Power –
Business and Technology for the Global Generation Industry.
Cooling Tower Study: Facts and Lessons Learned. 2007. Washington State Department of
Ecology.
Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve
Water Efficiency. 2011. U.S Department of Energy, Federal Energy Management Program.
Cooling Water Management, Basic Principles and Technology. 2008. Timothy Keister. ProChem
Tech International, Inc. Brockway, Pennsylvania. www.prochemtech.com.
Effective Use of Recycled Water in Cooling Towers with New Green Technology. Joe Walters,
West Basin Municipal Water District, Carson, Ca. Dan Duke, Water Conservation Technology
International, Techecula, Ca.
Water Quality Guidelines, Product and Application Handbook. 2012. Baltimore Air Coil
Company.
White Rust, Technical Resource Document. 2010. Baltimore Air Coil Company.