SWG in Public/Community Pools - How common are they?

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narukami

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Jan 5, 2010
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Does anyone know what percentage of Public/Community pools use a SWG for pool maintenance?

My community association has a old outdoor pool that has deteriorated to the point where repair is too costly. The association has decided to replace the pool rather than repair it. The decision to replace the pool involves substantial renovation for the community center. The new design plans convert the existing pool into three separate pools, two outdoor (1 wading pool (triangular shaped) and 1 general purpose pool ("P"-shaped pool)) and one indoor pool (rectangular shaped).

I do not know the number of gallons for each of the three pools nor their exact dimensions. The indoor pool is more or less a lap pool and is approximately 30 ft x 80 ft with a projected depth of about 4.5 ft. The general purpose outdoor pool is a bit larger and has a portion designated for diving, hence deeper in depth. The wading pool is approximately 1000 square feet and will have a maximum depth of about 1.8 ft.

This is an expensive project with many issues and options...one being the installation of a salt water generator for water maintenance. This option will add approximately $170,000 to the budget. This option is still being considered and debated. When the SWG option was presented, it was qualified with the statement that SWG were not installed in most public pools. It was presumed this statement was supported by data, but none was provided. It was just a generalization which most assumed was fact. I'm just curious to know if it is true and if there is any data to support the claim.

If it is true that most public/community pools do not use a SWG, does anyone know why the SWG is not popular for public pool use. If anyone has any knowledge about this, I would appreciate any information, advise and/or comments that would explain the claim.

Thanks in advance.

narukami
 
Welcome to TFP!

I don't have the data you want, but I can tell you where the (fairly small) bias against SWG usage in public pools comes from. The only significant issue is for indoor pools. Indoor pools have highly variable chlorine demand. When lots of people are swimming, you need lots of chlorine. But when no one is swimming you hardly need any chlorine at all. Every now and then you get a pool maintenance person who fails to do their job right, is not paying any attention, and leaves the SWG set on high over several days of very light pool usage. The result can be extremely high chlorine levels, significant metal corrosion and respiratory problem. There have been a few dramatic cases of this in the last couple of years, which has created some mild backlash against SWG in public pools. None of this is an issue for outdoor pools, where sunlight creates enough chlorine demand to keep chlorine levels from getting dangerously high. Also remember that nothing would have gone wrong in the first place if the person responsible for pool maintenance was doing their job.
 
narukami said:
The new design plans convert the existing pool into three separate pools, two outdoor (1 wading pool (triangular shaped) and 1 general purpose pool ("P"-shaped pool)) and one indoor pool (rectangular shaped).
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Commercial chlorine generators are well suited for both indoor and outdoor pools. One of the problems with indoor pools is that chlorine odors often overtake the building. This is caused by chloramines which are actually much worse for proper water chemistry than just the odor problems they present. With a chlorine generator you'll virtually eliminate chloramine issues.

narukami said:
This is an expensive project with many issues and options...one being the installation of a salt water generator for water maintenance. This option will add approximately $170,000 to the budget.
Click to expand...

Most commercial chlorine generator projects that we are involved in at community pools run far less than this. I would look around at several proposals.

narukami said:
This option is still being considered and debated. When the SWG option was presented, it was qualified with the statement that SWG were not installed in most public pools. It was presumed this statement was supported by data, but none was provided. It was just a generalization which most assumed was fact. I'm just curious to know if it is true and if there is any data to support the claim.
Click to expand...

I don't know of any industry data which shows a breakdown of traditional chlorine systems to chlorine generators in commercial applications. However more and more commercial/public facilities including water parks, military bases and YMCA locations are converting daily.

You want to make sure you're dealing with a distributor who knows how to properly size a commercial chlorine generator -- many don't know how to do this.
 
JoshU said:
You want to make sure you're dealing with a distributor who knows how to properly size a commercial chlorine generator -- many don't know how to do this.
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I assume there is a formula for determining the proper size SWG. Can you briefly explain what that formula is and/or how to properly size a commercial salt water chlorine generator for a combination of indoor and outdoor pools like our community is pursuing? It would be useful to know so that I can determine if size of the SWG being proposed by the designers is appropriate.

Thanks for your responses.

narukami
 
It depends on the bather load. State and county regulations vary somewhat in the maximum bather load allowed, but roughly speaking it's usually around one bather per 15 square feet in <= 5 foot depth and one bather per 20 square feet in > 5 foot depth. If I assume 3 foot shallow depth and 6 foot deep depth, then this works out to one bather in 337 gallons in the shallow end and one bather in 898 gallons in the deep end. If I assume a rough average of one person per 500 gallons, then the bather load from sweat and urine that is typically assumed to be 809 mg N / hour works out to a chlorine demand of around 3.4 ppm FC per hour. To give you a rough idea, this is 20 people per 10,000 gallons so is quite high, but not unheard of. This is also 13 grams per 1000 gallons per hour or about 7 pounds per 10,000 gallons per day, but that assumes people in the pool all day long which isn't realistic.

The NSF guideline is 3 pounds chlorine (ppm Cl2) per 10,000 gallons per day so they probably assume the bather load is not for 24 hours and they may use somewhat lower maximum bather load assumptions. Note that the above analysis does not account for extra organics getting into the pool such as dirt/soil, pollen, sunscreen, nor does it account for chlorine demand from skin. Some manufacturers use a rule-of-thumb of 1.6 pounds per 10,000 gallons per day for commercial/public pools. For residential pools, the SWG manufacturers usually size for a minimum of around 0.33 pounds per 10,000 gallons per day (4 ppm FC per day or 0.17 ppm FC per hour), but obviously the bather loads are presumed to be much lower in such pools and loss from sunlight is usually the dominant chlorine demand. Residential pool owners should generally get an SWG that is larger for longer life, probably at least 50% higher if not double this manufacturer recommendation (the pricing of SWG units is not linear with respect to sizing so it is generally worth getting a larger unit as they last roughly proportionally longer).
 

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