Oversizing SWCG - How much is Too much

[BasicTek]

So I was wondering if oversizing can actually be too much. In your case a t15 is built to last (or at least warranted) for 3 years on a 40K pool. Divide that by 6000 and for your pool (6.67 X 3) it should possibly last around 20 years (based on chlorine production). I'm in the same boat at the rate I use my t15 (avg 4 hours at 20%) mine should last 20 years as well (I have the turbo cell which is longer lasting) . Unless the t15 - t3 price difference is very small (in my case the installed price was almost the same as I was stuck with pool store prices) our cells end up dying of old age before they even reach 1/2 their chlorine producing potential (I don't know for sure but I figure my cell will die in 7-8 years max as well).

I take it you replaced your t15 with another t15, were you tempted to save $$$ and get a t9 or t3?

I also really love my hayward but would have to think long and hard on the circupool sale prices if I were buying now...

 

[Brentr]

Re: Oversizing SWCG - How much is Too much

So I was wondering if oversizing can actually be too much. In your case a t15 is built to last (or at least warranted) for 3 years on a 40K pool. Divide that by 6000 and for your pool (6.67 X 3) it should possibly last around 20 years (based on chlorine production). I'm in the same boat at the rate I use my t15 (avg 4 hours at 20%) mine should last 20 years as well (I have the turbo cell which is longer lasting) . Unless the t15 - t3 price difference is very small (in my case the installed price was almost the same as I was stuck with pool store prices) our cells end up dying of old age before they even reach 1/2 their chlorine producing potential (I don't know for sure but I figure my cell will die in 7-8 years max as well).

I take it you replaced your t15 with another t15, were you tempted to save $$$ and get a t9 or t3?

I also really love my hayward but would have to think long and hard on the circupool sale prices if I were buying now...

I replaced with a t-15 because it came with one and I prefer to stay with original parts. That being said as I understand the cell is good for 10,000 hrs and by my calculatuions I got that amount. The equipment experts can also comment here

 

[BasicTek]

Re: Oversizing SWCG - How much is Too much

I replaced with a t-15 because it came with one and I prefer to stay with original parts. That being said as I understand the cell is good for 10,000 hrs and by my calculations I got that amount. The equipment experts can also comment here

I here ya, and maybe you had to run your's more than me. I run mine in the summer about 4 hours at 20% so that would be less than 1 hour a day at 100% it would again take me over 20 years to use that up. The newer aquarites work with any Hayward cell just a quick change the programming. Unless as my cell gets older I have to crank up production I'm probably going to try a t3 next, but hopefully either way that's a long long way off as I get ready to start year 2 in April.

I totally understand the oversizing as a practice but in reality I barely have to use my cell which is just under 4x my pool. In theory I should be running closer to 6 hours at 100%.... When I asked about that a while ago everyone just said be happy and enjoy!

 

[JoyfulNoise]

Re: Oversizing SWCG - How much is Too much

There is/are no good reasons to undersize an SWG cell. If you oversize the cell and you get a long life out of it, then you minimize your overall chlorine costs, that can only be described as a positive. The life of the cell is entirely dependent on the transition metal oxide coating on the titanium plates. That coating is very thin and it gets degraded over time from low pH, acid washing and....actually cell use. Everytime your cell engages, a small amount of the coating is degraded. This is why the cell plates only have a rated lifetime of 10,000 hours (and that's optimistic) - that's about how long the coating will last under ideal operating conditions. So a larger cell that you run less often will last many more pool seasons than a smaller cell that you have to run harder. Likewise, running a cell at 100% output for long periods of time in less than ideal pool water conditions (your pool water is less than ideal as compared to what they test the cells in) can lead to high pH and calcium scaling. Acid washing a cell reduces the cell life considerably as strong mineral acids will degrade the coating.

The economics and chemistry of SWG cells is very clear - all things being equal, larger cells are always better.

 

[BasicTek]

Re: Oversizing SWCG - How much is Too much

The economics and chemistry of SWG cells is very clear - all things being equal, larger cells are always better.

Mathematically that can't be true Matt unless larger cells lasted forever. If you for instance have a 4K pool and buy a 60K cell the cell will die long before it ever produces the chlorine it is capable of producing. If you bought a 15K cell (still sized 4x the pool) it would probably last just as long as the 60K for less than 1/2 the price and still you'd be lucky if you reached 100% of the capable chlorine production.

The statements I've heard, here, and just about everywhere (which I don't think are wrong I'm not arguing with the 2-3x concept) is if you have a 15K pool you should buy a system that is 2-3X bigger because a 15K cell is sized to run at 100% for 24 hours. So in my case with 11K pool and a 40K cell I should have to run my cell approx (based on SWG calculator, hourly chlorine production, etc) about 6 hours a day at 100% or 12 hours a day at 50%. That's not exact but a ball park based on my cell being almost 4X the size of my pool.

However in reality my pool runs the cell for 4 hours at 20% in peak summer and 3 hours at 10% in the winter. It is virtually impossible that I will ever see my full chlorine production of this cell (not just the t15 but the turbo version with the larger plates)

If cells would last until their max chlorine production then sure you could always say get the biggest cell you can, but since they are probly never (or extremely rarely based on what i've read) going to last more than 10 years (probably less) Then there has to be a curve on the graph where you are buying too much cell.

If/when my current massively oversized cell every dies I'll put it to the test buy seeing how long I get out of a t3 but until then I would not recommend to anyone to size more than 3x unless the oversized system is almost the same price as a 3x or they just don't care about throwing money away and/or they want super short run times...

 

[JoyfulNoise]

Re: Oversizing SWCG - How much is Too much

Cell life is based on chlorine production time, that is actual ON time, not just some fixed length of time. So when one quotes the operational life of the cell as 10,000 hours, that's 10,000 hours of chlorine production time. So a larger cell on a smaller pool will have less "ON time" and therefore last many more seasons than a smaller cell. In other words, SWGs produce a fixed total amount of chlorine gas. So, if you buy a smaller cell, that's like buying fewer bottles of bleach or fewer bags of dichlor. As I said, other factors outside of just run time can impact cell life with calcium scale being the biggest cell killer.

If you haven't read it before, Richard (chem geek) did an economic analysis of SWGs based on available data and compared that to liquid and solid sources of chlorine. The basic takeaway is that one should oversize the cell so that you minimize the cost of the generated chlorine as compared to other sources (liquid or solid) and, if you look at the comparison of the different models from a specific manufacturer, a larger cell produces chlorine for fewer dollars over its lifetime and replacements than a smaller cell.

Economics of Saltwater Chlorine Generators

 

[Jimrahbe]

If I understand what Tim is saying.... he believes that a cell is likely to fail for some other problem, before the 10K hour limit has been reached.. when operated beyond five years of so..

I have no idea if that is true or not..

Jim R.

 

[BasicTek]

I see this was branched into a different thread when it in fact is a direct answer to the OP's question "Is bigger better or is there a point of diminishing returns?"

This quote from your link backs up exactly what I'm saying "This assumes that the cells actually last as long as indicated based on usage and that they do not degrade at all based on time alone. [EDIT] Note that the larger cells will output higher FC out of the returns (see this post) so for lower pump flow rates and/or smaller pools that could be too high an FC" and this "Note that at 2.0 ppm FC per day in 18,000 gallons, the IC60 lasting 10,000 hours in theory would be able to operate for (10,000 hrs)/((2.0 ppm FC/day)/(0.56 ppm FC/hr running)) = 2800 days or many, many years (over 7 years if used all year long)"

I have a tcell 15 that's rated for 40K pool and warranted (full warranty not prorated) for 4 years. my pool is only 1/4 that size so then simple math would say I will get 16 years for my pool. Then add to the fact that I don't need to turn the cell on anywhere near as long as expected for a 11K pool (possibly my screen weakens the sun, the 80 CYA, who knows) so now my cell being used again 1/4 as much as expected would then last for 64 years.... We all know that my cell no matter how little I use it will probably be dead long before 64 years or 16 years. When it comes time to replace the cell which has a little more than 1/3 the chlorine production would be a much better choice for my 11k pool.

I'll play with the SWG calculator, I'm pretty sure I can calculate the expected cell life based on my current usage and rated chlorine produced (assuming the cell out doesn't degrade) and it will most likely be around 30 years. The same calculation for a t3 should be more like 12 years which would still be a stretch.

Edited by Jim R. to remove Bold...

 

[mknauss]

(possibly my screen weakens the sun, the 80 CYA, who knows

And that is why your pool is an outlier. In a good way! There is NO doubt that your screen limits your UV and organics.

You might see I have an IC40 in a 6K pool. I have to run it at 50% for 7 hours each day in June, July, and August. I have strong SW desert sun and organics from neighbors with dogs and dirt back yards. My CYA is 70-80.

So every pool is different.

Take care.

 

[JoyfulNoise]

I understand your point of view - you are basically making the proposition that it's better to operate on the low margin and simply burn through cells and replace as-needed rather than take the gamble on a larger cell failing before its rated lifetime due to external factors. That is certainly one choice a pool owner can make but that choice has two distinctive features -

1. You are actually paying more for your chlorine than simply using chlorinating liquid and so the value proposition of an SWG vanishes;

2. You are requiring the pool owner to fork over large sums of money on a regular basis and that goes against the psychology of buyers in general.

It's kind of like leasing a car versus buying one - in the lease, you only pay for the part of the car that you use (sort of), then you trade it in for a new one every so many years. You endure the higher marginal cost because you'd rather not own a depreciating asset and/or you prefer to get new features. When you buy a car, the motivation is to own it for the longest period of time possible and drive it into the ground so as to maximize its utility and minimize the cost of ownership over the life of the car. Neither option is wrong but, in general, owning cars with full utilization is cheaper than leasing cars. As the old saying goes - The least expensive option for a new car is fixing the one you already own...

We have had folks on this forum get 10 years out of their cells and it coincided nicely with the stated operational life of the unit. Most of the failures to get full life out of cell we see here on TFP are caused by operator abuse and not following TFP guidelines. And since this community is only a tiny fraction of pool owners, the vast majority of failures will likely be just that - operator and service technician abuse/misuse.

With that said, you're correct, it is highly likely that you will not get 64 years out of your cell (you probably won't live long enough to see it). But your pool has many unique features that would allow you to go with a lower rated cell if you wanted to:

- Screened in pool enclosure reduces UV loss and debris load
- High CYA (80 and above) minimizes UV loss. In my own pool (completely uncovered) high CYA reduces my UV loss to less than 1-2ppm/day
- VSP allows you to run at minimal energy cost for chlorine production
- lower pool volume
- following TFP guidelines

So, here's the homework for you - run the cell to get the FC your pool needs each and every day and keep track of run time and output. Manage your pool all the time using TFP recommended levels and techniques. Then, ask the future owner of your home and pool to report back in 65 years when they have to buy the first replacement cell

 

[JamesW]

What are you using for the cell prices?

 

[Saturn94]

BasicTek,

I’m curious where you bought a T-15 cell with a 4 year non pro rated warranty? I’ve never seen one with that warranty.

(On the Hayward site the 4 year warranty 40k gal cell is the T Cell 940.)

 

[BasicTek]

You might see I have an IC40 in a 6K pool. I have to run it at 50% for 7 hours each day in June, July, and August. I have strong SW desert sun and organics from neighbors with dogs and dirt back yards. My CYA is 70-80.

That's true Marty, but even with that high 4 FC demand in summer I'd bet your average year round was closer less than half that meaning you should expect your IC40 to last you almost 20 years as well.

The OP in the thread was in canada and asking this question with a 7K pool. Anything over 25K would most likely be extreme overkill (I'd bet their annual usage would be less than both you're dessert sun and even my screened FL sun).

I’m curious where you bought a T-15 cell with a 4 year non pro rated warranty? I’ve never seen one with that warranty.

(On the Hayward site the 4 year warranty 40k gal cell is the T Cell 940.)

Leslies adds a year for the swimpure extreme (which is the extended t15 aka t-cell 940) I had them match a price at pinch a penny for $1149 which was the minimum to qualify for $100 hayward rebate (that dropped it to $1049) they also gave me a good price on install (around $100) and had a special for leslie bucks (between that and the intelliflo gave me back around $300). Since I had no pool experience that price in the spring was outstanding even for a pool store (the intelliflo was also discounted quite a bit)

 

[needsajet]

So every pool is different.

This is really important, and I'd also say that the owner's circumstances vary as well. Good question and great points made by all. Here's a couple others, speaking both 'for' and 'against' everyone's point of view, lol.

If you expect to sell your house or move before the cell wears out, a smaller cell can cost you less.

If you like to run an SWG hard, then you'll get more convenience and $ value out of your SWG with a very big cell. Running hard might include preferences such as e.g. using it to increase chlorine levels (not just maintain), using it to SLAM, or using it to be ready for a little kid's party or the dog coming back from a muddy run. I like running mine hard, and that's why I'll consider going bigger on a replacement cell even though I'm already "3x over-sized".

Also, if you're otherwise able to use extremely short pump run times, e.g. <2 hrs per day, no airborne contamination, especially with high bather load, then the larger cell could be an important choice, because of greater than usual savings in pumping cost. There's a similar potential effect on payback/lifespan if you're stuck with an over-sized single-speed pump that refuses to wear out, and your hourly pumping cost is higher than "normal".

 

[mknauss]

I am sure you are right on my average use. But when I purchased the ET package it cost me $100 to go the IC40 vs IC20. With the IC20 I would be running it at 100% for my 7 hours.

Our electricity cost is such that I like to minimize our pump run time to just while the sun is on the pool.

 

[BasicTek]

I am sure you are right on my average use. But when I purchased the ET package it cost me $100 to go the IC40 vs IC20. With the IC20 I would be running it at 100% for my 7 hours.

Our electricity cost is such that I like to minimize our pump run time to just while the sun is on the pool.

Same here (as noted on my last post I couldn't get the t9 or t3 for much less than the t15 in fact they were probably both more at leslies) but I did expect my t15 to need to run it at least twice as long. Now that I know my peak FC draw is not usually more that 1.5 and can be much less in the winter I would replace my t15 with a t3 (in 60 years if I'm still alive due to modern health breakthroughs Matt! )

What are you using for the cell prices?

In the original thread I was guiding the canadian based OP with 7K pool that anything in excess of 20K 3x sizing (based on circupools sale) could be overkill.

 

[BasicTek]

If you like to run an SWG hard, then you'll get more convenience and $ value out of your SWG with a very big cell. Running hard might include preferences such as e.g. using it to increase chlorine levels (not just maintain), using it to SLAM, or using it to be ready for a little kid's party or the dog coming back from a muddy run. I like running mine hard, and that's why I'll consider going bigger on a replacement cell even though I'm already "3x over-sized".

Also, if you're otherwise able to use extremely short pump run times, e.g. <2 hrs per day, no airborne contamination, especially with high bather load, then the larger cell could be an important choice, because of greater than usual savings in pumping cost. There's a similar potential effect on payback/lifespan if you're stuck with an over-sized single-speed pump that refuses to wear out, and your hourly pumping cost is higher than "normal".

Well I'm certain that my almost 4x oversized cell produces more FC than it's 1.45 rating probably closer to 2.5 - 3.0 based on the SWG calculator, so that throws all kinds of expected calculations off. I can certainly raise my FC to 25 in a single day (and did just before hurricane Irma). I can run my SWG an hour a day if I wanted but I have elected to run it 4 in the summer at about 15% - 20% and 3 in the winter at 5% because my pump is running anyway for the solar.

I do also suspect that I always have an issue with rising PH (more so than most SWG owners that aren't 4x+ oversized) because my cell is so oversized. It will likely be a very long time before I can actually tell, but I bet replacing my t 15 with a t3 (only 1.5 x my pool) it would be interesting to see how my PH acts.

 

[needsajet]

Is the 3 hours winter and/or 4 hours summer divided into multiple run times?

 

[BasicTek]

Is the 3 hours winter and/or 4 hours summer divided into multiple run times?

no. 11-2 in winter 11-3 in summer The pump runs from as little as 10:30-3:30 in winter to as much as 9-5:30 in the summer (for solar) and I use timer to keep the SWG inside that. Another thing is, even with these short run times and low %'s I still (just had to yesterday) accidentally over chlorinate and have to turn off the SWG for a day or 2. As my pool temp was up to 90 and the outside 85 the last week I upped my SWG from 3 hours at 10% to 3 hours at 15" and my FC was 9 yesterday oops, back to 10% lol