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Principle of Operation

Salt

Non-ionized, coarse, sun-dried or pelletized salt (normally in 40 lb. bags) is initially added to the pool water to develop a concentration of 0.5% (5,000 ppm).  This concentration of salt in the water is similar to that of human tears.  The saline solution is therefore very gentle to the swimmers’ eyes, skin and mucous membranes.

Electricity

A small amount of electricity is used by the chlorine generator during the electrolytic process.

Grounding of the pool system needs to be closely monitored

¨      In some situations, grounding wires and bonding loops may be grounded in different location.  This will create a potential in pool system.  All pool systems and equipment needs to be on the same grounding loop.  Test all equipment to confirm proper grounding.

¨      High conductivity along with the electrical process to create chlorine in the cell essentially “charges” the pool water and creates a “battery” in the pools system

The Electrolytic Process

Hypochlorous acid is produced when an electrical DC current is passed between the positively-charged anode plates and the negatively-charged cathode plates in the chlorinator cell.  This solution flows, after mixing into the water leaving the filter, directly into the swimming pool.

Sanitizing Effect

While the filtration system, which is linked to the electrical power supply of the chlorination system is operating, the system will introduce electrolytically produced hypochlorous acid into the swimming pool on a continuous basis.  The system does not operate unless the filtration system is operating.

This continuous introduction of hypochlorous acid ensures the continuous sanitization of the pool water and will provide the necessary chlorine residual required when the equipment is operated properly.  When the hypochlorous acid produced in the chlorinator has destroyed the bacteria in the pool, it reverts to salt (sodium chloride).  This means that salt is continuously recycled during this process.

Since the chlorine is ultimately converted back into salt, it gets recycled and extra salt will only need to be added infrequently (only a small amount will need to be added once or twice a year to replace the salt lost due to splash-out or backwashing).

o    Salt systems generate pure sodium hypochlorite at a near neutral pH and therefore have less effect on pH than most other pool chlorines.  The pH must be controlled like usual, and is influenced mostly by the total alkalinity of the water.

o    One gallon of liquid chlorine introduces three pounds of salt in a pool

o    Most chlorinators typically will operate at all times when the filtration system is operating.

o    Saline systems that spike the pool with salt increase the TDS levels to 3500 – 6000 ppm.  This causes several concerns:

  • Increases conductivity of water
  • TDS above 1500 is new to the market (unknown long term effects)
  • Saline pools were popular in the Canadian market throughout the 90’s, however, new information shows these systems being removed and replaced with traditional chlorine feed systems
  • Grounding of the pool system needs to be closely monitored

In some situations, grounding wires and bonding loops may be grounded in different location.  This will create a potential in pool system.  All pool systems and equipment needs to be on the same grounding loop.  Test all equipment to confirm proper grounding.

High TDS will accelerate the effects of corrosion in the pool

High conductivity along with the electrical process to create chlorine in the cell essentially “charges” the pool water and creates a “battery” in the pools system

o    The industry recently approved a new classification system to pools based on their TDS levels

  • Type 1 Pools:  0-1500
  • Type 2 Pools:  1500-6000
  • Type 3 Pools:  6000+

o    Many of the manufactures in the aquatic industry are uncomfortable “guaranteeing” their products in water over 1600 ppm TDS (Pentair, Marlow, Natare).

System Sizing #

Sizing of salt generators will be based on:

  1. Gallonage
  2. Surface areas
  3. Bather load per 24 hours
  4. Hours of operation
  5. Additional water features
  6. Location (indoors or outdoors)

Salt systems should be sized for peak bather load periods.  Back up feed systems can be utilized where bather loads cannot be anticipated, such as new pools, or pools with excessive load over a short period of the year, and during first two to four weeks of pool operation without the chlorine generation allowing plaster to cure.

Systems ranging in size from 1.5 lbs/day to 25 lbs/day in both vertical and horizontal configurations allows optimization of system to the body of water and equipment room

Optimum sizing yields greater operating efficiencies and costs

Outdoor sizing recommendations are 0.65 lbs/10,000 gals for low use; 0.80 lbs/10,000 for medium use; and 1.0 lbs/10,000 for heavy outdoor use (Must meet local health code requirements)

Indoor sizing recommendations are 0.4lbs/10,000 for low use; 0.5 lbs/10,000 gals for medium use; and 0.6 lbs/10,000 for heavy indoor use (Must meet local health code requirements)

Salt Calculations #

27 lbs of salt per 1,000 gallons will produce 3,000 ppm concentrations of salinity.

Broadcast the salt and allow to dissolve before turning on the equipment

After initial salting, operators will only need to replace salt lost through backwashing and splash out.

Salinity Comparisons #

  • Salt system - 3,000 ppm (Min)
  • Human eye - 7,000 ppm
  • Sea Water  - 30,000 ppm
  • Levels of dissolved salt (1500 to 7000 ppm) have a relatively insignificant effect on corrosion.
  • Less than ½ as salty as the human tear, most swimmers hardly taste the salt in the water.

Advantages and Disadvantages #

Manufacturers report the following advantages of salt systems (most of which are highly debatable):

  • Saves money
  • Fixed costs versus variable chemical costs
  • Improves the quality of the water and enhances bather comfort
  • Stabilizes pH and easier water balance
  • Enhances indoor air quality
  • Reduced pool maintenance and ease of operation
  • Lease payments are tax deductible as an operating expense
  • Corrosion Potential
  • 4 ppm of free chlorine is reported to be ten times more corrosive than 4,000 ppm in salinity.
  • Manufacturers state that salinity levels up to 6,000 ppm of NaCl do not show appreciable increase in corrosion.
  • Where improper grounding is present, increased salinity can increase the rate of galvanic corrosion.
  • High TDS Impacting Water Quality
  • TDS has no impact on water clarity.
  • Increase in TDS has been used as an indicator of increased organic concentrations because it can be measured.
  • Ideal eye comfort solutions are approximately 9,000 ppm of NaCl.

Saline systems that spike the pool with salt increase the TDS levels to 3500 – 6000 ppm.  This causes several concerns:

¨      High TDS will accelerate the effects of corrosion in the pool

¨      Increases conductivity of water

¨      TDS above 1500 is new to the market (unknown long term effects)

The industry recently approved a new classification system to pools based on their TDS levels

¨      Type 1 Pools:  0-1500 ppm

¨      Type 2 Pools:  1500-6000 ppm

¨      Type 3 Pools:  6000+ ppm

Many of the manufactures in the aquatic industry are uncomfortable “guaranteeing” their products in water over 1600 ppm TDS (Pentair, Marlow, Natare).

Demand Recovery Time

Saline generation with a redundant feeder system should be recommended in all commercial applications where salt is being designed.

Maintaining 5 ppm as target residual with an appropriately sized system will allow up to two times the normal demand to be accommodated.

Taste Concerns

3,500 ppm is generally considered to be the normal taste threshold

At 5,000, the salt taste is detectable but not offensive

As an example, chicken soup has approximately 4,400 ppm of NaCl

Impacts on Water Balance

Saline generators have the least impact on pH of any commonly used sanitizer (reported between 7.7 and 8.8 pH).

Saline generators do not contribute to calcium, sulfates, alkalinity or stabilizer levels.

The salt is reused and regenerated continuously being lost only throughout splash out, water leakage, draining or backwash.

Initial costs

For most pools, the reported payback of saline systems is 2 to 4 years

Cell Life Considerations

Determined by size of cell, quality of the plates, maintenance,  and usage (run times)

Smaller residential type cells generally last only 3,000 hrs

Commercial self-reversing cells can last approximately 30,000 hours.

TMI Salt Pure’s X-series has a warranty of 3 years or 15,000 hours.

General Maintenance

Salt cells

Self-cleaning capability (reverses polarity)

Periodic manual cleaning required

Simple dilution of 5 parts water to 1 part of acid

Saline systems are often desirable on LEED projects (where feasible).  Using table salt with the saline system to create chlorine means that there is no longer a need to store commercial chlorine at a facility as chlorine will be manufactured in-line as needed.  Instead, bags of salt will be stored.  Also, by converting to CO2, facilities can eliminate the need to store and use muriatic acid and eliminating the potential for spills.  By removing most of the hazardous product from the pump room, facilities eliminate the potential for any accidental spills or cross contaminations of chemicals causing fires and or toxic off-gassing, making the facility more environmentally-friendly.

LA County and Santa Clarita do not allow the design of saltwater pools.

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