11,000 gallon pool with frequent high bather load (25-30 people)

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QPSUtah

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Sep 12, 2024
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Trying to help a client determine whether to go with an automated liquid chlorine system or a salt cell generator. It's a rental property in the mountains and during ski season they will have 25-30 people in a relatively small pool, 11K gallons, for days on end. My instinct is to go with a liquid chlorine system. If I assume an IC40 generates 1.4lb/day and a bather consumes 9 g/hr (taken from a spa figure I found elsewhere, so assume worse case scenario), with 30 people (again, worse case), then that is .6 lbs/hour. If they're in there more than 2 hours/day, seems like the salt cell would have a lot of trouble keeping up.

Perhaps I answered my own question here, but maybe we need to direct them to an automated liquid chlorine system.
 
This sounds like a commercial pool and should follow any local regulations for chlorination of a commercial pool.

What CYA level will be allowed and maintained?

Chlorine and bather load

I understand the target and min levels of chlorine but how do I determine if i need extra chlorine for bather load. Do I turn up the SWG before the party or after? Do I dose with liquid and how much? Last summer the water went cloudy after a few kids spent the afternoon in the pool. I think I...
www.troublefreepool.com www.troublefreepool.com

A rough rule-of-thumb is that the chlorine demand from bather load in swimming pools is around 4 grams of chlorine per person-hour. In a 7500 gallon pool, this is only 0.14 ppm FC per person-hour. This is why you mostly see chlorine loss from sunlight being the dominant factor and not notice much change when there are just a few swimmers in the pool. However, if you have a pool party and have 10 people in the pool, then 1.4 ppm FC per hour is significant and even in a larger pool the demand would be noticeable.

Bather Load Rule of Thumb / Cedar Hot Tub

Hello all, I've been reading up on chlorine and bather load, and on this forum I see a recurring statement, with an reference by the TFP Expert chem geek: "A rough rule-of-thumb is that the chlorine demand from bather load in spas is around 7 grams of chlorine per person-hour." I've searched...
www.troublefreepool.com www.troublefreepool.com
 
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It's a private rental, so I don't believe it's subject to commercial pool inspections, etc. If we go with a liquid chlorine set up, I'd likely target 40 and if we go with a SWCG, would target 60 or so, per the CYA/Chlorine chart here on TFP.

If I use the 7 g/hr figure, then 30 bathers are using up 210 g/hr, while the IC40 can generate up to 53 g/hr. I'm at a production deficit every time my bather load gets up to 7 or 8 people. Still leads me to believe I would want to go with a liquid system in this scenario.

Edit: Silly me. Calculated g/hr incorrectly for the IC40. Should be more like 26 g/hr assuming 1.4lb of chlorine/day involves 24 hour production.
 
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An IC60 can do about 38 grams per hour, but it is not that simple.

Bathers produce chemicals that create persistent disinfection byproducts like trichloromethane and haloacetic acids, which do not get oxidized easily.

The levels of CCs can quickly get out of control.

You probably need a commercial UV system to manage CCs.

You might be able to use an ORP to control output, but that gets tricky with CYA in the water.

You can use 0 to 30 ppm CYA to allow ORP control.

You also need significant dilution on a regular basis.
 
Trying to size a SWCG for an 11K pool. The challenge is, the bather load can vary dramatically. It can sit empty for weeks on end and then a large group will rent the home and perhaps have 10-20 people getting in and out of the pool throughout the day. It's a unique situation where half of the pool is outdoors and half indoors with a garage door style divider that goes up and down. So for the higher demand days, I'd like to have an IC60 to make sure we have more than enough headroom for chlorine demand, but perhaps the IC40 would also be fine.

I've done the math and looked at the output spreadsheet and modeled both the IC40 and the IC60. My concern is if there are not any swimmers, and the IC60 is running 8 hours per day, my chlorine may rise faster than my FC loss, but I'm not sure that would be in a covered, unused pool. If I model 0.1 FC demand, then the chlorine is regenerated in 6 hours at 2%, so running at 8 hours/day, minimum, will create 0.15 ppm/day in the pool at 2% level, the lowest.

I'd go with an automated liquid chlorine system, but the pool room is only accessible down a steep embankment in the snow during the wintertime, unless one goes through the house, and then there is the risk of chlorine dripping here and there (I've noticed the 5 gal and 15 gal containers aren't always fail safe in that regard).
 
JamesW said:
You can use 0 to 30 ppm CYA to allow ORP control.
Click to expand...
If you have an outdoor pool, the SWG will reach a dynamic equilibrium with the FC loss caused by UV because the loss rate increases with FC level and the loss rate will eventually reach the gain rate.

With an indoor pool or a covered pool, you do not have UV loss, so the levels can quickly get out of control.

You can test the FC levels several times a day or you can use some type of monitor like ORP or PPM.

A significant advantage of this PPM sensor is that it’s not affected by cyanuric acid (CYA) stabilizer and/or oxidizers, thereby assuring constant Free Chlorine levels at all times.

Unlike other chlorine sensors on the market, this new sensor is easy to install and maintain and gives the operator precise and reliable control of Free Chlorine under the most difficult conditions.

The PPM sensor is covered by a full 2-year warranty.

Chemtrol PPM monitoring and control option for swimming pool chemical controller provides direct, reliable readings of free chlorine (HOCL) concentration in water.

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CH265 pH / Free Chlorine Digital Controller - CHEMTROL

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Solid state sensor features superior precision and control of chlorine level

The most complete line of PPM sensors for direct measurement of CHLORINE in water. | Exceptional Quality, covered by a 2-year warranty | Call 1300 585 820
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Chlorine Analyzer - PCA300 Family | Hanna Instruments

Hanna Instruments Chlorine Analyzer continuously monitors, controls, and adjusts chlorine and pH levels to maintain safe and efficient concentrations.
www.hannainst.com
 
JamesW said:
If you have an outdoor pool, the SWG will reach a dynamic equilibrium with the FC loss caused by UV because the loss rate increases with FC level and the loss rate will eventually reach the gain rate.

With an indoor pool or a covered pool, you do not have UV loss, so the levels can quickly get out of control.
Click to expand...
You might be able to use a commercial UV system to provide some control of excess FC because the loss rate will increase as the FC level increases.
 

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JamesW said:
If you have an outdoor pool, the SWG will reach a dynamic equilibrium with the FC loss caused by UV because the loss rate increases with FC level and the loss rate will eventually reach the gain rate.

With an indoor pool or a covered pool, you do not have UV loss, so the levels can quickly get out of control.

You can test the FC levels several times a day or you can use some type of monitor like ORP or PPM.

A significant advantage of this PPM sensor is that it’s not affected by cyanuric acid (CYA) stabilizer and/or oxidizers, thereby assuring constant Free Chlorine levels at all times.

Unlike other chlorine sensors on the market, this new sensor is easy to install and maintain and gives the operator precise and reliable control of Free Chlorine under the most difficult conditions.

The PPM sensor is covered by a full 2-year warranty.

Chemtrol PPM monitoring and control option for swimming pool chemical controller provides direct, reliable readings of free chlorine (HOCL) concentration in water.
Click to expand...
Great! This is incredible. I just perused the installation manual, but SWCG's aren't specifically mentioned, such as the Pentair IC40 or IC60, but it works with them?
 
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