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Salt Water Systems Gaining Popularity for Pools
Published: July 22, 2008
By Connie Sue Centrella
Swimming pools are a cool refuge for residents this time of year, and maintaining them could become easier with the evolution of salt water systems. Salt water systems are now gaining in popularity for a number of reasons, including the reduced handling of chemicals by staff and potential cost savings.
While the initial installation is more expensive than that of the traditional chlorine erosion feeder, the process continually makes chlorine without the need to manually add additional tablets to a feeder. Therefore, while the initial cost is more, over a period of time, pool managers will notice a reduction in not only the cost of tri-chlor tabs or hypochlorite tabs, but also in transportation costs and storage involved.
Background
Electrolytic Chlorine Generators (ECGs), more commonly known as salt water systems, were first introduced in the late 1970s for swimming pools and spas when the technology was unknown to the swimming pool industry. This same process, invented in the 1960s, had been widely in use for wastewater treatment and industrial applications. Since the late 1990s, there has been a major shift in acceptance. ECGs have now gained worldwide approval. It is now recognized as the best methodology for generating chlorine sanitizer for both private and public pools and spas.
How they work
Salt is added to the pool or spa to establish a 3,000 ppm concentration. This is equal to only 7 percent of the salinity level in seawater. The pool user cannot taste the salt at 3000 ppm as this level is below the normal taste threshold; it is also less than the human body’s salt concentration of 4000 ppm.
One of the best features of this electrolytic process is that the salt continuously recycles itself. Adding salt is infrequent, normally in outdoor pools about two or three times a year; indoor pools require less frequent additions. Indoor air quality immediately improves as well when the salt system is utilized.
An electrolytic cell or cells is installed in the recirculation system after the filter and heater. As the filtered water flows through the cell, a small amount of DC current is applied to the cell blades, which under electrolysis, produces pure chlorine and sodium hypochlorite (liquid chlorine). As the water passes through the cell, the electrolytic process causes break-point chlorination, destroying bacteria and chloramines which are the source of chlorine odor, red eyes and most of the negative reactions blamed on chlorine. After oxidation occurs in the pool or spa, the sodium hypochlorite reverts back to salt in the pool. The process repeats itself over and over based on the chlorine demand in the pool or spa.
2NaCl (salt) + 2H2O (water) yields (under electrolysis)
2 Na HOCL + H2 gas
The micro bubbles of hydrogen gas exit the pool water invisibly.
Chlorine Demand Factors
There are eight factors that affect chlorine demand. These are:
• Volume and surface area of the pool.
• Average water temperature.
• Level of cyanuric acid (CYA) maintained. CYA slows down the destruction of chlorine by the sun’s ultraviolet rays in outdoor pools.
• Bather load. As the number of bathers’ increases, so does the sanitizer demand.
• Amount of direct sunlight/UV exposure. More sunlight exposure increases the rate at which sanitizer is consumed.
• Exposure to vegetation and airborne debris. Dense landscaping increases nitrates, which consume sanitation.
• Chemical dilution due to rainfall, backwashing, etc. Loss of water also creates loss of sanitizer.
• Main filter runtime and pool circulation patterns. Sanitizer is only introduced when pump is running. Waterfalls and other water features increase the demand for sanitizer.
Benefits
The major benefit to the pool operator is that Electrolytic Chlorine Generating Systems provide a safe method of sanitization. There is no need for bulky, heavy containers of powdered chlorine or tablets. There is no possibility of a chlorine leak or inexperienced personnel mixing chlorine with other dangerous chemicals. Erosion feeders, which have been the cause of many accidents, are eliminated from this process. Liability is one of the major factors in swimming pool operation and the installation of a safer salt generator chlorination system eliminates the exposure.
Very little chemical adjustments are necessary. Organic sanitizers such as tri-chlor have a pH range of 2.8 to 3.5 which inherently lower the pH of the pool water, requiring the addition of sodium carbonate to raise the pH. The chlorine generator produces a near neutral pH.
Another advantage is that the equipment installation is easy and does not take up much room in the mechanical area. There are only four components to the system: the power supply, the electrolytic cell, flow protection device and of course, salt which is dissolved in the pool water.
The systems today are now enhanced with digital readouts which allow the operator to precisely manage the pool water quality. The pool manager has confidence, knowing that there is continuous chlorine sanitation (and localized super-chlorination in the cell) occurring thus eliminating potential occurrences of poor water quality and exposure to diseases.
And finally, the patrons of the pool facility will enjoy a feeling of soft, silky water with no red eyes, itchy skin, faded swimwear or chlorine smell. The comfort level of users is enhanced as there is no chlorine smell in indoor installations. Keeping our visitors comfortable and coming back is key to operating a successful pool complex.
As with any system, to operate a safe and healthy pool, it is important to monitor water chemistry and equipment through regular testing and observation.
Drawbacks
There is a growing number of "commercial pools" that are being converted; I would estimate that at least 15 percent of the pools will be converted this year.
The conversion process is relatively easy. Just install the unit, arrange for some minor electrical and plumbing changes, and add salt according to the manufacturer's recommendations.
There are only a few objections. These include the initial cost of the units; however, the ease of maintenance and not having to handle traditional tri-chlor and cal-hypo tables offset this objection. Tri-chlor adds cyanuric acid which at higher levels may inhibit chlorine activity.
There is a slight increase in the pH of the pool water; however, a small amount of muriatic acid should to added to offset this increase.
There is a possibility of scale buildup on the cells which can be remedied by cleaning the cells periodically with a mild solution of muriatic acid.
Connie Gibson Centrella is a professor for the online aquatic engineering program at the Keiser University eCampus. She was twice honored with the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation as well as manufacturing.
For those looking to achieve a college degree program in the aquatics field, the Keiser University (www.keiseruniversity.edu ) Associate of Science Aquatic Engineering degree offers a two-year degree consisting of 60 semester hours, offered exclusively online.
To comment, contact Teresa O'Dea Hein at thein@multi-housingnews.com
