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Water Softening/Conditioning

Hot Topic: Salt usage calculation

October 13, 2010
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POSTED:

Posted by Jeff Hough on 9/2/2008 at 4:44:49 PM
Does anyone have a calculation to give them an idea of how much salt is needed to regenerate a softener?

I have a customer (a retired engineer) and he is looking for a formula that he can use to help him figure out how much salt he is going to need during a certain time frame. I wasn’t aware of a formula, so I thought I would ask the group.

The customer has a 60,000-grain softener, with two people in the house and a water hardness of 110 grains.


RESPONSES:

Gary Schreiber, CWS VI: 9/2/2008 5:03:57 PM
With that high hardness I would recommend 15 pounds per cubic foot (lbs./ft.3) of resin salt dose. If the softener is a demand-initiated unit, then set it to regenerate every 400 gallons. If it is time-clock regenerated, set for every other day.

There is no formula to use. They can regenerate at a lower salt dose, but the hardness leakage will usually be unacceptable at lower salt doses.

Roger Garrett: 9/3/2008 12:05:14 AM
What does the manufacturer say? Is this a co-current or counter-current regenerating softener?

A standard calculation for salt usage could be done as follows: [No. of people x gallons per person in one day x 110 (hardness)] ÷ efficiency of salt exchange. 2 x 65 = 130 x 110 = 14,300 grains in one day. Divided by 2,000 grains removal per pound of salt equals 7.15 pounds per day. 90 days at 7.15 = 643.5 pounds.

More water uses more salt. Metered and counter-current could cut the amount in half, as the exchange rate is about 4,000 grains per pound of salt. If counter-current: 2 x 65 = 130 x 110 = 14,300 ÷ 4,000 = 3.575 x 90 days = 321.75 pounds.

All this is based on calculations, not the real world. Older folks usually use less water. Exchange efficiency is calculated by manufacturers, sometimes using “not-real-world testing” to create better numbers.

The ability to program the unit accurately, meter the flow properly, etc. is critical. This proves that specs are important and can mean a huge difference in operating costs. Just try adding up the cost of operation over a 25-year period of delivered salt at today’s prices.

John July: 9/3/2008 9:30:00 AM
You said the customer has a water softener. How long has he had it? As Gary and Roger asked, is it time-clock or metered? What valve/controller is it? If the unit has been in service and working, what values have been set up in the controller?

Jeff Hough: 9/3/2008 2:12:13 PM
Thanks to all who have responded. … The customer has a GE Logix controller that has been installed and operating for approximately two weeks. I was able to patch together a rough formula using pieces from several different Web sites and came up with a formula similar to the one Roger posted. …

R. Ross Derksen: 9/3/2008 5:52:59 PM
In this case, formulas are only a starting point. You will not get rated capacity on 110-grain water. Do the calculations, and then de-rate the softener capacity 25 or 30 percent. If you salt at 15 lbs./ft.3 as Gary suggests, then de-rate the softener to 45,000 grains. This is easy to do with the Logix controller. There will be some hardness bleed no matter how much salt you use, but you will have less at the 15 lbs./ft.3. If I were using the 762 Logix I might try 12 lbs./ft.3 and de-rate the capacity 25 percent, and see if the hardness bleed was acceptable. If you have the 760 Logix you are going to have to use the H salt setting, which is going to be 15 lbs./ft.3.

John July: 9/3/2008 6:48:05 PM
With only two weeks on line, you won’t yet have an idea of the actual gallonage consumed, so I would use the 75 gallons per day (gpd) per person average and tell him they would likely use 150 gpd. I’m assuming that this is the 760 Logix. If you regenerate only based on gallons, you can view the data and calculate what the controller will do. In the history mode, you can see how many gallons have been used since the last regeneration. In the service or normal display mode, you’ll see how many gallons will be used before regeneration. Add the two together and you can figure out how many gallons before it will use salt.

In the normal programming mode, you will see what the controller thinks the capacity is, based on what was entered as cube size and salt setting.

As suggested, it would be better to run the unit in the H (high) salt setting, which is 15 lbs. per one cube. The cube size programmed will be the first display in the history mode (page 43 in your manual).

As time goes on, you’ll be able to go back and view how many gallons have been used and refine the annual salt consumption based on the customer’s use. Unfortunately, the 100 gallon totalizer rolls over at 65,536 gallons, so you need to record the values annually if you want to keep records.
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