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Old 05-15-2012, 04:31 PM   #1
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Final hardness and salt dosage


I recently posted these questions on someone else's thread because they were somewhat on topic. I'm reposting to create a new thread with the replys quoted


A couple of questions:

1. I am wondering how to adjust the final hardness of softened water. The reason for this is that I am installing a condensing water heater that requires that hardness be maintained between 5 and 7 gr/gal. I am starting with water that is 13 gr/gal. I have read that reducing the salt dosage allows the final hardness to be above 1 gr/gal, but it is not clear to me by how much.

2. I understand that SFR is 7gpm/cuft. (although I have seen references to it being non linear). How does one avoid channeling? Is there a minimum flow/cuft? I assume that channeling doesn't occur just because a low flow is being demanded over the short term (a single low flow tap on for 2 minutes). It must occur over a longer time if insufficient peak flow rates don't occur often enough.

3. How does softening affect TDS?

4. I have read much about salt dosage and brine efficiency, but I don't understand how to set it up. I don't see mention of salt dosage in the programming manuals for the 2510SXT, 5600SXT or 7000SXT. It is briefly mentioned in the 6700 Upflow manual. How is it set in these other controllers? Seems like I'm missing something.

5. I'm not too concerned about hardness leakage if SFR is exceeded on occasion. Why is it mentioned so much? I don't see a problem with occasional briefly elevated hardness or am I missing something (again)?

6. What is upflow brining? Is it more difficult or expensive? How much more brine efficient is it? Is it more water efficient?

7. My intention is to use one of the above Fleck valves. Any opinions about them? I am having a hard time finding a good comparison of the features and capabilities.

Thank you,

Chris

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Old 05-15-2012, 04:33 PM   #2
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Final hardness and salt dosage


This was the first reply:

Quote:
Originally Posted by Bob999 View Post
1. To adjust hardness you must blend raw water and softened water to achieve the desired hardness. Adjusting salt dose is not a reliable way to control hardness--if you adjust the salt dose down you will get soft water (less than 1 grain/gal) for a while and then when the resin is exhaused the hardness will rise to that of the softened water. But with regard to the requirements in your installation manual note it say soft water MAY be under saturated... Do a search for the Langelier saturation index and do the computations to see what the index would be for your water if softened--you may not have a problem with soft water.

2. The service flow of a 1 cubic foot softener is typically described as 9 gallons. A properly sized and regularly regenerated softener won't have channeling problems.

3. Softening changes TDS very little-perhaps a very small increase.

If you provide a complete water analysis and the specific softener you have I can suggest salt efficient settings. If you provide family size, specifics of special fixtures like multihead showers and large tubs or anything else than would increase your overall water usage or typical flow rates I can suggest an appropriate size softener with your water analysis.
Quote:
Originally Posted by Bob999 View Post
What brand/model of condensing water heater requires this? Could you please provide a link to the literature that requires this?

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Old 05-15-2012, 04:34 PM   #3
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Final hardness and salt dosage


Bob asked what water heater required 5-7 gr/gal hardness, to which I replied:

Quote:
Originally Posted by cgarai View Post
Hi

Heat Transfer Products is the manufacturer, Phoenix Solar is the specific product I will be installing. You can find the installation guide here:
http://www.htproducts.com/literature/lp-179.pdf
The reference is on p.15.
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Old 05-15-2012, 04:36 PM   #4
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Final hardness and salt dosage


Quote:
Originally Posted by Bob999
1. To adjust hardness you must blend raw water and softened water to achieve the desired hardness. Adjusting salt dose is not a reliable way to control hardness--if you adjust the salt dose down you will get soft water (less than 1 grain/gal) for a while and then when the resin is exhaused the hardness will rise to that of the softened water. But with regard to the requirements in your installation manual note it say soft water MAY be under saturated... Do a search for the Langelier saturation index and do the computations to see what the index would be for your water if softened--you may not have a problem with soft water.

This clarifies some things and muddles others. I could not see how salt dosing would affect final hardness, but I had read that here:
http://www.apswater.com/water_softener_capacity.asp

As for the Langelier Saturation Index, I did as you suggested, but come to no conclusion. Here is why.

I used 2 website calculators:
http://www.cleanwaterstore.com/techn.../langlier.html

http://www.lenntech.com/calculators/.../langelier.htm

and both come up with slightly different numbers. I then put the formula for LSI into a spreadsheet and came up with slightly different numbers again. The formula I used is here:
http://www.corrosion-doctors.org/Coo...-Langelier.htm

It is possible I used the wrong numbers in the formulas I "guessed" that what the online calculators refer to as Ca2+ is hardness in mg/L.

One thing I noticed that makes a big difference is the final hardness. My LSI goes very negative with .1gr/gal and very positive with 2 gr/gal. This is evident in the formula as the log of small numbers gets more negative. If water softeners really suck all the hardness out then the water is very corrosive according to the LSI


Quote:
Originally Posted by Bob999
2. The service flow of a 1 cubic foot softener is typically described as 9 gallons. A properly sized and regularly regenerated softener won't have channeling problems.

I'll use that figure. I have seen 7 GPM/cuft in one place and another mentioned a non-constant figure varying from 9 gpm/cuft at 1cuft to 6.5 gpm/cuft at 2cuft.

Quote:
Originally Posted by Bob999
3. Softening changes TDS very little-perhaps a very small increase.

If you provide a complete water analysis and the specific softener you have I can suggest salt efficient settings. If you provide family size, specifics of special fixtures like multihead showers and large tubs or anything else than would increase your overall water usage or typical flow rates I can suggest an appropriate size softener with your water analysis.


You asked for it!

4 people, 3 full baths. One bath with two shower heads and a large tub. My estimation is that most of the time flow rates will not exceed 10gpm and even if they do I don't mind some hardness leakage.

Our water usage over the last year has been 100gal/day for the whole family (25gal/day/person). That comes directly off the water bill. We currently live in a house that requires no irrigation. This calculation is for a house we are building, which is bigger and may lead to less frugal habits, but I hope not too much!

In short, 10gpm and 40 gal/day/person are the figures I'm using.

Water Analyisis:

Alkalinity 189 mg/L
pH 8 mg/L
Hardness 12 Gr/gal (205.2 mg/L)
Iron 0 mg/L
TDS 300 mg/L
Manganese 0.53 mg/L


Based on all the above I get calculate:

160 gal/day
1920 grains/day

Usage is calculated as 7 days + 1 day reserve.
Usage based capacity in cuft:
.51cuft 15#salt/cuft
.77cuft 6#salt/cuft


SFR based capacity is 1.11 cuft
capacity in grains is 33,333 grains

Basing this on a 32k system, I estimate that at 6#/cuft recharge, I should get 11 days between recharges at 160 gal/day. If we actually maintain our usage at 100 gal/day then it goes up to 18 days.

Did I come close?

Thanks!!

Chris
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Old 05-15-2012, 04:37 PM   #5
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Final hardness and salt dosage


Bob's response was:

Quote:
Originally Posted by Bob999 View Post
There is an important difference between agressive and corrosive water. The LSI is an index of aggressiveness--specifically the tendency of the water to attract (read dissolve) calcium carbonate that it comes in contact with. This is an important measure for things like water districts that use concrete pipes and swimming pool operaters with concrete or plaster pools. Not so important for fiberglass or vinyl pools or pvc piping systems. Also not so important for good quality stainless steel.

Corrosive, on the other hand, is much more related to acidity. I note you have somewhat alkaline water so corrosion is not really an issue and softening doesn't change pH.

I think it is important to note that the literature you posted a link to conditions the warranty on suitable TDS and pH--but in no way conditions the warranty on hardness or the lack of hardness. However, your pH is right on the edge of breaking the warranty.

On the other hand the discussion on p 15 talks about hardness resulting in build-up of lime scale and "may result in premature failure of the heat exchanger ". I know from personal experience that hardness of 6 or 7 grains will cause significant buildup on heat exchangers in a remotely fired hot water heater.

You may want to seek further opinions but mine is that you would probably be better off using your water--but softened-- than using your water blended with softened water to achieve a hardness of 5-7.

Based on your data and your stated willingness to live with higher leakage on occasion I suggest a 1 cubic foot unit with it programmed for a capacity of 16,000 grains, regenerated with 5 lbs, and 8 days override. But you may find that the manganese causes problems with these settings. If so you will need to increase the salt dose--first try 6lbs to see if it resolves the problem and if not then try 7 lbs.
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Old 05-15-2012, 04:47 PM   #6
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Final hardness and salt dosage


Hi Bob, will use your recommendations as they seem to correspond with what I calculated, indicating I might have a clue ;-).

I did come across the original notion that caused me to believe that salt dosage did have an impact on final hardness. It comes from the Purolite C100-E resin data sheet



I pinched this image off another forum, but the original data sheet is available at:

http://www.purolite.com/Customized/C...ces/rid_62.pdf

This seems to contradict what you originally posted, but perhaps I'm misinterpreting the data sheet.


Thanks,
Chris
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Old 05-15-2012, 05:10 PM   #7
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Final hardness and salt dosage


Oops, that graph doesn't really contradict, I misread the units. It is still very low <1gr/gal leakage. I read gr/gal not ppm, as printed.

Chris

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