Replace SWCG: Cell size vs. Runtime etc

[acroy]

Please check my reasoning! Bear with the long-ish description: :blah:

My SWCG is undersized: 25k unit in a 33k pool. It’s also getting old (5yrs) so I’m researching a replacement. I’m trying to determine optimal cell size given the needs.

A caveat is that the big 2.25total hp pump easily keeps the pool clean and filtered in 4hrs of runtime. It adds substantial cost to run the pump extra hours just to let the SWCG keep up.

The math:
1ppm Cl = 3.8g of Cl per 1,000gal
Thus, 33k pool needs 125g Cl to raise the FC 1ppm

Assume the SWCG needs to generate 3ppm/day given load & sunlight (reasonable?)

125gx3 = 375g Cl to be generated per day

Biggest easily available SWCG I can find is the CompuPool 60k model, which generates 46g/hr. This puts runtime at 8hrs to generate 375g Cl, much longer than the pump needs for filtering/cleaning. An option is to replace the pump motor with a 2spd model to enable longer runtime with lower utility cost. Timer (basic on/off mechanical) would also have to be replaced to enable the cleaner to work at high speed for an hour or 2, then switch to low speed. I’ve not yet put the dollar sign together on this.

Any feedback or suggestions? Thanks!

 

[openpool]

I've read of some people suggesting more than one cell in parallel in case the dollar amount for more than one SWCG is feasible for you.

 

[JasonLion]

3 ppm/day is much more than most SWG pools use. Actual usage should be closer to 1 or 1.5 ppm/day in most situations, though this will of course vary depending on the amount of direct sunlight on the pool and how many people are swimming.

Switching to a two speed motor will save you a substantial amount of electricity, as well as making it much easier to keep the SWG happy.

 

[acroy]

Thanks JasonLion for the feedback

If the math is right, the current cell should be able to add 1-1.5ppm per day 5-8hrs runtime. I've been sticking to 4hrs a day and supplimenting with bleach as needed. I'll try running 8hrs for a week or 2 and see if it can keep up.

At 8hrs a day, payback period on a new motor looks to be about a year, not including a new timer.

 

[Strannik]

we sell units that go up to 100g/h in residential range and unlimited in commercial, but they wouldn't be economical on your pool and not easily available in USA although we do ship there.

i'd probably go with Jason's suggestion of a low speed pump

 

[drvegster]

Thanks for your post -- I found your thought process very useful. I am presently thinking of replacing an Autopilot system with an Intellichlor and am trying to size it appropriately.

I found that the Autopilot SC-36 at 1.28 lbs Cl/day did not cut it, even though it certainly should have for my 15Kgal pool. But the SC-48 at 1.56 lbsCl/day seemed to fit the bill. When it worked... I have intermittent dual flashes that mean connectivity problems and am really tired of finding it randomly failing.

Most pertinent to your post, I am interested in how you arrive at
1 ppm Cl = 3.8 g Cl / 1Kgal. Would you please explain? Much appreciated.

 

[JasonLion]

Adding 1 ppm of chlorine to 1,000 gallons requires 2.07 oz of 6% bleach or 0.134 oz, ie 3.8 grams, of chlorine gas. SWG cells are usually rated by the equivalent amount of chlorine gas they would produce. You can use those numbers to calculate from when comparing SWG cell ratings to how much chlorine you are currently using.

 

[drvegster]

Thanks. Very useful info.