Hayward OmniLogic Doesn't Match Test Results

[Furiousss]

My test shows 2800ppm and instant reading shows 3443.

Is it reasonable that my OmniLogic should display an accurate salt reading? 23% difference seems pretty significant.

 

[mknauss]

Hayward Aquarite SWG - Further Reading

www.troublefreepool.com

The Aquarite does not measure salinity. It infers a salinity from the performance of the cell.

 

[JamesW]

My test shows 2800ppm and instant reading shows 3443.

Close enough.

Just go by the box, but keep comparing the two to see if the difference stays the same or if it changes.

 

[JamesW]

To get the performance of the cell, divide the instant salinity by the actual salinity.

If the ratio is less than 75%, it's time for a new cell.

For example, 2,000 (instant salinity) ÷ 3,600 (measured salinity with a test kit)=56%.

Check the cell and clean it if necessary.

If that doesn't work, it's time for a new cell.

3,443/2,800 = 1.23.

So, your unit is actually performing at 123% of expected performance.

 

[Furiousss]

Close enough.

Just go by the box, but keep comparing the two to see if the difference stays the same or if it changes.

It's pretty consistently off by a few hundred ppm with the Hayward always reading higher than the actual salinity. Looking at the link posted above, I take that to mean my cell is >100%.

 

[Furiousss]

To get the performance of the cell, divide the instant salinity by the actual salinity.

If the ratio is less than 75%, it's time for a new cell.

For example, 2,000 (instant salinity) ÷ 3,600 (measured salinity with a test kit)=56%.

Check the cell and clean it if necessary.

If that doesn't work, it's time for a new cell.

3,443/2,800 = 1.23.

So, your unit is actually performing at 123% over expected performance.

I guess that's "good", and it would make sense since the cell was only used for the first time last September. Disappointing to learn that "instant salt" isn't what it says, but it makes sense. I'll use it as outlined in the link and continue to evaluate salinity with my tests.

Thanks

 

[JamesW]

All salinity readings have a margin of error.

The actual salinity is probably somewhere between the two readings.

In any case, keep testing to see how the two compare.

The cell performance should stay level for a few years and then it will begin to drop as the life gets used up.

 

[JamesW]

The actual salinity is probably 3,120 ppm +/- 300 ppm to 95% certainty.

 

[Furiousss]

All salinity readings have a margin of error.

The actual salinity is probably somewhere between the two readings.

In any case, keep testing to see how the two compare.

The cell performance should stay level for a few years and then it will begin to drop as the life gets used up.

If the test can't be fully relied upon either, then how do I know when to add salt? I thought 3200ppm was ideal. Maybe the range is broader than I thought?

 

[JamesW]

Just go by the box and make sure that the reading is not too low.

Since you have a heater, I would keep the salinity as low as possible without triggering the low salt warning, which happens at 2,700 ppm on the box.

The problem is that when the heater kicks on, the amps go way up due to the water temperature and this can trigger a high salt warning at 8.0 amps.

So, your margin of error is very tiny and it is difficult to manage the salinity in the tight range.

If it was my system, I would change the cell type to T-9 to make the box read higher and keep the actual salinity at about 2,400 to about 2,800 ppm.

Note: Hayward does not recognize doing this, so I do not recommend that anyone do this.

I am just saying what I would do; not what you should do.

 

[JamesW]

For example, if the cell type is set to T-9 when you have a T-15, the salinity will read about 1.48 times too high.

For example, if the actual salinity was 2,600 ppm, then the box will read 3,848 ppm.

This will allow you to run the heater without hitting 8 amps and it will also not trigger the low salinity reading.

Note: I am not recommending that you do this.

If you do this, it is completely at your own risk.

 

[Furiousss]

Just go by the box and make sure that the reading is not too low.

Since you have a heater, I would keep the salinity as low as possible without triggering the low salt warning, which happens at 2,700 ppm on the box.

The problem is that when the heater kicks on, the amps go way up due to the water temperature and this can trigger a high salt warning at 8.0 amps.

So, your margin of error is very tiny and it is difficult to manage the salinity in the tight range.

If it was my system, I would change the cell type to T-9 to make the box read higher and keep the actual salinity at about 2,400 to about 2,800 ppm.

Note: Hayward does not recognize doing this, so I do not recommend that anyone do this.

I am just saying what I would do; not what you should do.

This site almost unanimously advises a salt cell 2x its pool volume. Hayward's biggest cell is 40k gallons, so 1.67x my pool volume. My impression had been that I was slightly undersized, but "close enough".

So I understand, you're saying the fact that I have a heater flips this on its head?

Would a heater bypass change your advice? I asked for one - the pool builder said it was pointless. Pretty sure I could add one now anyway.

 

[JamesW]

When the heater turns on, the water temp exiting the heater increases by about 16 degrees.

This causes the amperage to go higher.

For example, if the amperage with the water at 84 degrees is 7.0 amps, the amperage can hit 8.0 amps at 100 degrees water temperature.

It is a design defect for the Hayward Salt system (In my opinion) because the salinity has to be so tightly controlled to avoid a high salinity shutdown, which triggers at 8.0 amps regardless of the actual salinity.

 

[Furiousss]

Interesting. I haven't actually used the heater yet (well, once last year for a few hours to verify it worked). I don't actually recall whether the salt cell was turned on yet at that point.

 

[JamesW]

Note that I am not saying that you should change the actual cell; I am saying that I would probably change the cell type selected in the configuration settings so that it tricks the system into reading the salinity as higher than it actually is.

 

[JamesW]

Interesting. I haven't actually used the heater yet (well, once last year for a few hours to verify it worked). I don't actually recall whether the salt cell was turned on yet at that point.

Watch the cell readings when the heater turns on to see how much the water temperature and current (Amperage) go up.

You will see the water temperature go up by about 16.8 degrees (at 40 gpm) and the amperage will increase by about 1 amp or more.

 

[JamesW]

Heater outlet temperature rise will depend on the water flow rate.

Slower water flow will have greater outlet temperature since the same BTUs go into less water volume.

Changing the pump speed can vary the return temperature from just warm at high RPM to very hot at minimum flow for the heater.

For example, a 400,000 btu/hr heater with an efficiency of 84% transfers 336,000 btu per hour to the water.

At a minimum required flow of 40 gpm, there will be 2,400 gallons of water (20,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

336,000 btu into 20,000 pounds of water is 16.8 degrees of temperature rise (336,000/20,000).

So, the maximum temperature rise you should ever have is 16.8 degrees Fahrenheit.

As shown below, higher flow results in a lower temperature rise.

40 gpm = 16.8 degrees temperature rise
50 gpm = 13.44 degrees temperature rise
60 gpm = 11.2 degrees temperature rise
70 gpm = 9.6 degrees.
80 gpm = 8.4 degrees.





This shows the expected temp rise (Y-axis) vs. Flow in GPM (X-axis).

The minimum required flow is 40 gpm.

So, the maximum temp rise should be 16.8 degrees Fahrenheit.

 

[JamesW]

Some people like to keep the water temperature at 90 degrees, or higher.

This can make the water exiting the heater 106.8 degrees, or higher, which increases the amperage of the cell significantly and this can trigger a high salt warning if the amperage hits 8.0 amps even if the salinity is 3,200 ppm, which is the recommended level.

 

[ajw22]

Don’t try and fix a problem you do not have. Run your SWG the standard way. All is fine with your setup.

Never add salt based only on the panels readings. Always test with your salt test kit before adding salt and keep the actual salt level at 2800 - 3000 ppm.

 

[JamesW]

My point was that it can become a problem in some cases, so the poster needs to be aware of when it can be a problem and what options are available for making the system work.

For pools over about 86 degrees, the high amp shutdown can become a problem when the heater turns on even if the salinity is in the "Normal" recommended range.

For example, if the water was 92 degrees, you pretty much could not use the Aquarite without triggering a low and/or high salt warning.

As soon as the heater turns on, the water goes to about 109 degrees and the amperage goes to 8.0, or higher, even if the salinity was 2,800 ppm.

You can keep the salinity below 2,800 ppm, but then you get the low salt warning.