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Cooling Tower Water Treatment

 

HVAC systems that keep commercial locations cool create a tremendous amount of heat in doing their job. Cooling towers used in these applications do the job of removing the heat from these systems and keep everything cool and efficient. Vaporization of the latent heat is what helps accomplish this cooling effect. For every pound of water that evaporates in a cooling tower approximately 1,000 BTU’s of heat are removed from the liquid that remains in the cooling tower. The more water that is evaporated, the more cooling power the tower exerts.

All water sources have minerals and solids that are carried in the water that is used in cooling towers. During evaporation the water is removed but the solids remain. They circulate through the cooling tower system and become increasingly concentrated in the water passing through the system. In addition to the salts and solids contained in the water the air used to cool it contain nutrients, dust, gases and microorganisms that are scrubbed out of the air and end up deposited in the cooling tower’s re-circulating water.

Cycles of Concentration

This is a comparison between makeup water and the condition of the water that has been cycled through the cooling tower. The solids carried in the water due to the evaporative nature of the cooling tower and the particulates being scrubbed out of the air contribute to the condition of the water. The industry standard for comparing the source water to the re-circulating water is by measuring the chloride content in both.

Treatment Of Cooling Tower Water

The most sensitive area for water treatment is when contaminated water is re-circulated through the chiller tubes. Certain inorganic substances and biological contaminates are attracted to the heat transfer elements. If these effects are not mitigated by treating the cooling tower water these contaminates collect and coat in the inside of these heat transfer elements. This insulates them and can dramatically reduce the thermal performance of chiller tubes. They can also corrode chiller surfaces and reduce the flow through the chiller overall. Bacteria, scale, biofilm, and corrosion are the four most common issues in the operation of evaporative cooling technologies.

Bacteria Control

For decades the deadly Legionella bacteria has been a recurring problem is cooling towers. The naturally warm environment found in cooling towers along with other biological matter and organic debris help promote the development of the Legionella bacteria. Biocides are used to control the growth of legionella and cooling tower maintenance involves using alternating types of biocides. This alternation of chemicals helps prevent the bacteria from becoming resistant to any one compound. Legionella is relatively difficult to kill because of its resistance to two of the most common water treatment chemicals, bromine and chlorine. Chlorine dioxide and ozone gasses are regarded as highly effective treatments for legionella.

Despite the effectiveness of chlorine dioxide and ozone gasses they are not widely used due to the cost and expertise necessary to administer the program and maintain the equipment that must be used to produce the gasses on site.

Controlling Scaling

Makeup water that is heavy in inorganic salts cooling towers can suffer from scaling on heat exchange equipment. Scaling can prevent the heat transfer surfaces from efficient thermal performance. This will lead to a higher condensing temperature and lower the capacity of refrigerant. In turn the cooling system will require more energy to do its job and will raise the costs. The build up and scaling of calcium is one of the most problematic issues. It precipitates from the solutions at warmer temperatures when in the presence of carbonate alkalinity. Organic polymers and acids are frequently used to prevent and remove these scaling problems. Acids levels must be managed carefully as improper levels of acidity will cause corrosion and premature mechanical failure.

Controlling Biofilm

The systems used in cooling tower systems create an environment for a number of microorganisms. These organisms end up deposited on the metal surfaces in your system and can dramatically reduce your cooling tower’s energy efficiency. These deposits limit the thermal transfer 6 times more so than scaling, due to their higher level of insulation.  To treat the biofilm issues Chlorine Dioxide Gas and ozone are two of the most effective processes. This is due to the fact that these microorganisms are resistant to bromine and chlorine.

Controlling Corrosion

Corrosion is the degradation of metal parts in your cooling tower. This is caused primarily due to the corrosive acidic chemical additives used in cooling towers. There are some microorganisms that also produce acid that has a corrosive effect on the cooling tower. When some chemicals are used to control scaling, bacteria, biofilm and white rust corrosion is a possibility. When corrosion is the result of the chemicals used to control microorganisms it is the fault of the water treatment program. The program should not allow Microbiologically Influenced Corrosion (MIC) but should also not promote excessively high acidic conditions. Once a MIC has been allowed to develop in your system it is hard to eliminate. Prevention is the key to avoid the highly levels of hydrogen sulfide, sulfuric acid, and other corrosive elements.

Controlling White Rust

White rust is possible in new cooling tower systems. It is a serious condition found in new galvanized steel components and cooling towers. They stem from substandard start-up procedures, or the failure to passivate the new cooling tower properly. This condition is made worse by high alkalinity in softened water. Cooling tower manufacturers have guidelines for proper passivation protocols and should be followed when a new cooling tower is installed. While they vary to some degree the use of inorganic phosphates is common. The initial alkalinity should be between 6.5 and 8.0. The heat load should also be controlled during the phase of passivation.


Cooling Tower Water Treatment in Phoenix AZ

If you have a cooling tower in the Phoenix area All Kote’s technicians are highly trained and skilled at chiller and cooling tower maintenance and repair. We can help treat the water, clean the equipment, and apply coatings to help minimize the loss of thermal performance of your HVAC chillers and cooling towers. Give us a call to discuss your industrial cooling towers and what your needs will be in getting the best performance out of your equipment.

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