Jandy Aquapure PLC1400 SWCG scale build up after a few weeks, only on the output "grate"

[JamesW]

What is the power usage at 20 gpm for each configuration?

 

[TaylorN]

What is the power usage at 20 gpm for each configuration?

I captured these wattage figures a year or two ago in just the Pool setting (no solar), but they should be close. I'll re-capture tomorrow with each configuration at 20gpm.
1400rpm [117w]=7-8gpm
1600rpm [170w]=10gpm
1800rpm [256w]=11-12gpm
1900rpm [306w]=14-15gpm
2000rpm [367w]=19gpm
2050rpm [402w]=20gpm
2200rpm [467w]=23-24gpm
2850rpm("high" speed) [1080w]=39-40gpm
3100rpm [1419w]= 42-43gpm
3450rpn [2151w]= ??gpm

 

[Stoopalini]

Have you considered if the SWCG is generating when the pump shuts off, the stationary water left in the SWCG has altered temp and pH (and CSI) due to the way the electrolysis process works? This could be causing scale to occur quicker than it would if the flow was continuous, or if the SWCG would stop generating a bit before the pump shuts down, to flush the high temp / high pH water out of the cell before the water stops moving.

Especially since heat rises, and you have that 90* and U turn at the top ... it would seem reasonable to think the warmer water is resting at the top of the cell which is where the output is; and where you are seeing the scale.

This is one of the reasons I run my pump 24x7 at 1200 RPM. 2 years in, and I have zero scale on my plates.

 

[Stoopalini]

Just to add ... looking at your plumbing, I would want a check valve here if the pump is not going to run 24x7. If the SWCG is generating when the pump shuts down, you have highly chlorinated water in that vertical pipe. The hot water rises and sits at the top (most likely causing the scale at that end), and the cooler water falls bringing highly chlorinated water into the heater.



With 117w at 1400 RPM, why not run the pump 24x7 and not have to deal with the highly chlorinated, high temp, high pH water remaining in that vertical pipe after the pump shuts down?

Google tells me electric rates in San Diego county is $0.34 per kWhr, on average, and since your pump is off for 13 hours now, here's what it would add to add those 13hrs and run it 24x7:

117w x 13hrs = 1,521w (or 1.52 kW)
1.52 x $0.34 = $0.52 per day
$0.52 x 30 days = $15.50 per month
Or, about $190 a year extra.

$190 a year to not have build up on the cell (assuming that's what is causing it) and also to not have highly chlorinated water back feed into the heater, seems like a good deal to me ...

If you have solar with battery storage at your property, it would be even better.

Seeing those rates, I'm happy to be living in Texas ... I pay $0.09 per kWh ... which means it cost me $0.30 a day to run my pump 24x7. I think if I were in California, solar power generation would be required for my home...

 

[Stoopalini]

Ohhh, I just thought of something else.

You can alter your schedule to run the pump at some RPM well below the SWCG flow switch, just for say 10 mins, after the normal operation.

So 6am - 5pm at 1400RPM, then 5:00pm to 5:10pm at say 600RPM. This way, the SWCG would turn off due to the flow switch, but the water would continue to circulate at 600RPM for another 10 mins ... flushing the high chlorine, high temp, high pH water out of the vertical pipe.

And if you did this, it wouldn't increase your electric bill at all.

 

[wireform]

If the SWCG is generating when the pump shuts down, you have highly chlorinated water in that vertical pipe. The hot water rises and sits at the top (most likely causing the scale at that end), and the cooler water falls bringing highly chlorinated water into the heater.

I'm not sure I understand the advice here. The SWCG can NEVER be able to be powered while the pump is not running. I there's power there when the pump is off it just wired wrong and asking for a chlorine gas explosion. With a SWCG it isn't necessary to have a check valve as when its off nothing is there that'll affect the heater. If it was a chlorinator that would be a different story then you'd need a cv.

 

[Stoopalini]

I'm not sure I understand the advice here. The SWCG can NEVER be able to be powered while the pump is not running. I there's power there when the pump is off it just wired wrong and asking for a chlorine gas explosion. With a SWCG it isn't necessary to have a check valve as when its off nothing is there that'll affect the heater. If it was a chlorinator that would be a different story then you'd need a cv.

Let's say the pump is running, and the SWCG is set for 30% cycle time.

This means the SWCG's electrolysis process is activated for 20 mins of every hour (ie: 30% of the time).

So at 6pm, when the OP's pump cycle ends, and the pump turns off ... if the SWCG is inside one of those 20 minute periods, where the SWCG is generating, then it shuts down along with the pump ... but, the highly chlorinated, elevated temp, high pH water is still in the pipe ... but now without any circulation going.

It's not that the cell is generating while the pump is off, but it was generating when the pump (and cell) turned off.

If the pump could run for another couple of minutes without the SWCG generating, it would flush that water out of the pipe.

 

[HermanTX]

I installed the FlowVis Flowmeter and at 1400rpm the pump is only running at 7-8gpm. The Jandy manual for the SWCG says to run a minimum of 20gpm. However the low flow sensor doesn't come on until 1200rpm and everything I have read on the forum about RPM for SWCG is that you should go as low as you can until you get the low flow light to turn on and then increase the RPM by 100-200rpm, hence using as little electricity as possible. That is how I ended up at 1400rpm. It seemed to produce enough chlorine, but I am obviously now trying to analyze all the variables since the cell is scaling quite quickly (not on the plates, but the electrodes/grate), even though the saturation index is not terribly out of whack. Going to use a calibrated salt/tds sensor tomorrow to get a more accurate reading of that.

here is the following GPM breakdown at various RPMs.

NO SOLAR heating
Pool:
1400rpm=7-8gpm
1600rpm=10gpm
1800rpm=11-12gpm
1900rpm=14-15gpm
2000rpm=19gpm
2050rpm=20gpm
2200rpm=23-24gpm
2850rpm("high" speed)=39-40gpm

Spa mode:
1400rpm=7-8gpm
2050rpm=20gpm
2150rpm=21gpm

Spillover:
3100rpm= 42-43gpm

WITH SOLAR heating (half of the array is on 1st story, half on 2nd story)
Pool:
2200rpm=19gpm
2300rpm=20gpm

Note, I thought it would have taken a lot more RPM to push water up to second story vs not having solar turned on. Looks like only a difference of ~200rpm to get to 20gpm

Back in post #4 you had noted that the SWCG was not in proper direction per the Jandy manual. Did you decide to change that to the other vertical pipe or put it on horizontal pipe?

 

[mknauss]

but, the highly chlorinated, elevated temp, high pH water is still in the pipe .

You are searching for a problem that does not exist. The bulk water in swcg is just not that ‘highly’ chlorinated nor high pH.

 

[Stoopalini]

You are searching for a problem that does not exist. The bulk water in swcg is just not that ‘highly’ chlorinated nor high pH.

I'm not searching for a problem, just providing some input on a probable cause for an existing problem the OP is experiencing.

My comments above are based on information I learned from one of the TFP "meet the experts" YouTube session. Where you guys had discussed the environment inside the cell, when the electrolysis process is engaged, being prone to causing scale due to high temp and high pH. And flushing the water out after the generation stops, or running the pump 24x7, would help avoid premature scaling.

Seeing the OP's plumbing orientation, and the fact he is getting scale only at the top of the cell, made me think of that discussion.

 

[mknauss]

The high pH is at the plate surface. Once the chlorine gas is absorbed into the water, the pH is neutralized.

 

[Stoopalini]

I think it was @JoyfulNoise who was commenting on it during the YouTube session. If I remember correctly, he even mentioned using borates to reduce the pH rise happening in the cell as a way to mitigate against the scaling.

In any case though, it's pretty easy for the OP to set the pump to run for an additional 10 mins at an RPM below the SWCG's cutoff, at the end of his normal pump cycle, just to see if it makes a difference. If it doesn't there's nothing lost.


I thought the pH rise was neutralized only when the chlorine completes it's cycle, meaning it acts on some contaminate in the water .... producing an acidic reaction at that time. I didn't realize the act of the chlorine gas being absorbed into the water itself, was an acidic reaction which lowers pH.

 

[JoyfulNoise]

So that's taking what I said out of context and making huge assumptions about what's happening inside the cell. Let me now clarify -

@mknauss is mostly correct - all of the chemical reactions are happening at or near the cell plate surface. Borates act as a strong buffer when the pH is close to 9.0 (that is roughly the pKa value of the borate/boric acid equilibrium). So, when the cell is generating chlorine and producing hydroxide anions, some of that rise in pH is going to be absorbed by the presence of borates. That helps right in the vicinity of the plate surface. Also, calcium ions will be in equilibrium with the carbonate and bicarbonate as well as borates so any scaling that occurs will be a mixture of various calcium precipitates. Calcium borate tends to be mushier and easier to remove than calcium carbonate. But again, this is only at the surface of the plate. As soon as the cell is de-energized, the pH will very quickly go back to normal because the flow rate through the cell is very fast.

What causes scale at the leading edge of the cell (the exit) is a little complicated but it is due to the fact that the electric field produced by the cell when it is running gets protruded outwards along the flow path of the electrolyte. This protruding electric field and electric current tends to cause higher current densities at the edges and can even result in a current path to ground if the plates are not sufficiently offset. All of this results in the formation of scale at that edge preferentially to any place in the cell. This type of scaling is a very common feature in flow cells.

I doubt "flushing the cell" will have any noticeable effect. The OP might try reducing the pump speed and flow rate through the cell to see if that helps at all.

 

[Stoopalini]

Gotcha, I guess I did take it out of context ... for reference, this is to what I was referring ... where you mention the main cause of the calcium scaling is due to the high pH of the water inside the generator. My mistake, and I apologize for any confusion I may have caused.

As soon as the cell is de-energized, the pH will very quickly go back to normal because the flow rate through the cell is very fast.

Out of curiosity, what about when the flow through the cell stops at the same time the cell is de-energized? Does the pH of the water inside the cell go back to normal through some other mechanism when there is no flow?

 

[TaylorN]

So that's taking what I said out of context and making huge assumptions about what's happening inside the cell. Let me now clarify -

@mknauss is mostly correct - all of the chemical reactions are happening at or near the cell plate surface. Borates act as a strong buffer when the pH is close to 9.0 (that is roughly the pKa value of the borate/boric acid equilibrium). So, when the cell is generating chlorine and producing hydroxide anions, some of that rise in pH is going to be absorbed by the presence of borates. That helps right in the vicinity of the plate surface. Also, calcium ions will be in equilibrium with the carbonate and bicarbonate as well as borates so any scaling that occurs will be a mixture of various calcium precipitates. Calcium borate tends to be mushier and easier to remove than calcium carbonate. But again, this is only at the surface of the plate. As soon as the cell is de-energized, the pH will very quickly go back to normal because the flow rate through the cell is very fast.

What causes scale at the leading edge of the cell (the exit) is a little complicated but it is due to the fact that the electric field produced by the cell when it is running gets protruded outwards along the flow path of the electrolyte. This protruding electric field and electric current tends to cause higher current densities at the edges and can even result in a current path to ground if the plates are not sufficiently offset. All of this results in the formation of scale at that edge preferentially to any place in the cell. This type of scaling is a very common feature in flow cells.

I doubt "flushing the cell" will have any noticeable effect. The OP might try reducing the pump speed and flow rate through the cell to see if that helps at all.

Wow! Thanks for stepping into this conversation @JoyfulNoise

So you are actually saying the more you reduce the flow through the cell the less scaling should take place at the leading edge of the cell (the exit)? The flow was at like 6-8gpm @1400rpm so I was assuming I couldn't/shouldn't go much lower.

Speaking of GPM, what are your thoughts as to why Jandy recommends a minimum flowrate of 20gpm? Before reading your response I was thinking by increasing the flow rate to 20gpm+ maybe the scaling wouldn't have a chance to settle because the water is blowing by it much quicker.

And do you think the vertical orientation of the cell has anything to do with it? Once again that orientation is not listed in the Jandy manual. They show it in a downward (exit on bottom) configuration, but I can't think of a reason why that would really make much of a difference.

And lastly, if borates make for a more mushy scale, then maybe I should incorporate borates into the chemistry so the scaling doesn't stick as much and the water flow would tent to carry it off the metal?

Thanks!

 

[JoyfulNoise]

Gotcha, I guess I did take it out of context ... for reference, this is to what I was referring ... where you mention the main cause of the calcium scaling is due to the high pH of the water inside the generator. My mistake, and I apologize for any confusion I may have caused.

Out of curiosity, what about when the flow through the cell stops at the same time the cell is de-energized? Does the pH of the water inside the cell go back to normal through some other mechanism when there is no flow?

We’re really only talking about a very thin layer of water near the plate surface. So whatever happens to be generated in the cell the second you cut off the power and the flow, is going to equilibrate with the larger volume of the cell rapidly. I’d doubt you’d be able to detect much of a pH rise. It never hurts to end the SWG cycle with water still flowing. I alway run a slow skim program (very low speed) that brackets my actual POOL mode when the SWG is running.

Wow! Thanks for stepping into this conversation @JoyfulNoise

So you are actually saying the more you reduce the flow through the cell the less scaling should take place at the leading edge of the cell (the exit)? The flow was at like 6-8gpm @1400rpm so I was assuming I couldn't/shouldn't go much lower.

Speaking of GPM, what are your thoughts as to why Jandy recommends a minimum flowrate of 20gpm? Before reading your response I was thinking by increasing the flow rate to 20gpm+ maybe the scaling wouldn't have a chance to settle because the water is blowing by it much quicker.

And do you think the vertical orientation of the cell has anything to do with it? Once again that orientation is not listed in the Jandy manual. They show it in a downward (exit on bottom) configuration, but I can't think of a reason why that would really make much of a difference.

And lastly, if borates make for a more mushy scale, then maybe I should incorporate borates into the chemistry so the scaling doesn't stick as much and the water flow would tent to carry it off the metal?

Thanks!

Maybe in your case try running the SWG at higher speeds to see if there’s a difference. Perhaps the slower speed is the cause. Most SWGs have 15-20 GPM as their flow rate spec. I would stay close to that.

 

[Stoopalini]

I alway run a slow skim program (very low speed) that brackets my actual POOL mode when the SWG is running.

That's exactly what I was suggesting for Taylor ...

 

[TaylorN]

Maybe in your case try running the SWG at higher speeds to see if there’s a difference. Perhaps the slower speed is the cause. Most SWGs have 15-20 GPM as their flow rate spec. I would stay close to that.

Ok. I will try 20GPM for a while and see what happens.

Thanks for the quick response!

 

[TaylorN]

Thanks for all of your time thinking about this @Stoopalini ! I am going to try 20gpm flow for a week or so and see if that clears up the scaling. If it doesn't I will definitely try your low flow idea (to force the cell off) at the end of the day's run. And yes, Southern California energy rates are insane! Jealous of Texas!

 

[TaylorN]

Back in post #4 you had noted that the SWCG was not in proper direction per the Jandy manual. Did you decide to change that to the other vertical pipe or put it on horizontal pipe?

@HermanTX , I haven't replumbed the SWCG, but I may put it in a horizontal position at some point if GPM adjustment doesn't correct the scaling