However, here is what I presume to be the case:  I don’t think soft water on its own affects efficiency much.  From a chemical engineering / mass transfer perspective, a few hundred mg/l of hardness will not show up as a factor in any driving forces related to the exchange of ions on the functional groups during regeneration.  Regenerating with soft water does, however, significantly affect the effluent quality when the resin is back in service.  There has been a lot of work demonstrating the improvement in quality when regenerating with treated water, whether it is soft, decationized or deionized water.  Obviously there are several factors that affect the effluent hardness from a softener, but generically I would say treated water (soft) would improve the effluent quality by an order of magnitude.  Again, this is difficult for us to isolate from the benefits provided by counter-current regeneration with a strong-acid resin.

Dave Chew

Director – Marketing & Technical Service

Kinetico Incorporated

Ok, here we go (I apologize for the long post):

QUOTE>I am told that softeners regenerated with softened water have a higher salt efficiency than a softener regenerating with hard water. I am also told the resin will last longer if regenerated with softened water. I do not agree with either claim. We are not talking of high iron fouling or high iron removal capabilities.<

Resin life depends on a variety of things, but let’s look at the big three:

1.  Fouling:  Well, certainly if there is nothing in the water that could foul the resin, then the resin would not foul in any softener regardless of design.  But I think that is an unreasonable limitation to place on the influent water.  Foulants are a contributing factor to resin life, so it sounds like you agree that if there are foulants present then the soft water regeneration would be an advantage.  I would argue that even at low concentrations, iron and other foulants do affect resin life, and regenerating with treated water helps.

A second factor here is that manufacturers set up their equipment to regenerate based on a capacity they expect to reach at equilibrium, months or years down the road.  It is well documented that even moderately fouled resin will exhibit significantly lower capacity in normal use (technically, fouled resin doesn’t have less capacity, just much worse kinetics).  So although it takes two steps to get there, I would stand behind a claim that soft water regeneration helps to resist fouling, which maintains working capacity and results in higher efficiency.

2. Oxidation: Not affected by regeneration design.

3.  Osmotic shock:  Resin can only shrink and swell so much before it begins to break down.  Two factors here: 1) Frequency of regeneration and 2) The concentration of brine used. If I can’t convince you that a counter-current regenerated system is more efficient and results in fewer regenerations for a given volume of water treated, then you won’t believe there is a difference here.  More on that later…

It is obvious, however, that a system which regenerates only when necessary, i.e. one that has the ability to regenerate any day at any time is inherently more efficient (at least by a factor of 7/6 at 1 regeneration per week).  This is simply because there is no need for a buffer or heal of sodium-form resin required to last the remainder of that day.  By definition, only twin-tank systems can regenerate at any time without getting hard water to service.

QUOTE> I say that as long as both types of softeners have the same volume of the same type of resin, and the same salt dose in lbs, both types will have the same K of capacity and the same salt efficiency.<

Definitely not the case.  See documents produced by just about every resin manufacturer discussing their particular branded countercurrent resin systems (you may have to become a licensed user to see their actual calculations).  Upcore, Liftbed, WS, etc.  A packed bed, countercurrent system is indeed more efficient.  For the last 20+ years I’ve had two different spreadsheets for calculating efficiencies and setpoints when designing systems:  One for co-current and another for counter-current (actually now it’s one spreadsheet; I just click a radio button to choose between the two).  In 1984 we released a softener that regenerated in 11 minutes using 9 gallons of water and 1 pound of salt.  5600 grains removed per pound of salt.  There is no way I could design a strong-acid, co-current softener with that kind of salt efficiency that worked in the real world.  Believe me I wish I could because a co-current, single tank system is significantly less expensive to manufacture!  I suppose you’d like me to just send over the calculations, but I’m not willing to do so.  There has been significant sweat (and tears!) over the years expended in creating our knowledge-base related to the regeneration of various ion exchange resins for softening, deionization and metal recovery. Dare I call it “intellectual property?” 

If you really want to know the “why and how” of the chemical and physical forces behind the difference, I would suggest reading “Transport Phenomenon” by Bird, Stewart and Lightfoot; especially chapters 16-19. It’s an old, tedious book.

But I’ll try to save you from that painful experience.  If you imagine what goes on at the boundary layer during regeneration, you’ll see every molecule of hardness being driven off individual functional groups by the concentration gradient of brine, on to the next one it sees then off that one and so-on through the bed from the top down.  This happens trillions of times during each regeneration.  Of course the top of the bed is the most exhausted, so the brine must work that much harder to exchange the hardness.  It takes a significant driving force to regenerate down into the center of the resin bead because of the mass transfer effects.  A co-current system has to do that through the entire bed.  A counter-current regeneration doesn’t have to work nearly as hard.  You’ll have to connect the rest of the dots.

QUOTE> As I see it, as long as the same volume of brine (lbs of salt) are used, the marketing department's sales brochures may be able to claim a higher salt efficiency (grains/lb) but, the consumer wouldn't see any difference between that softener and one that uses co current and hard water regeneration with the same lbs of salt.<

I don’t understand that statement.  If a softener removes more grains per pound of salt, then the customer will indeed use less salt.  Given a constant influent hardness, the softener with a higher usable grains/lb will use less salt.  Gallons used x gpg = grains.  Grains / [grains/lb] = lbs of salt used.  If the two softeners have the same salt setting during regeneration, then the one with the higher grains/lb rating will be set up to regenerate less often, i.e. more gallons will be processed between regenerations.  Notice the volume of resin is nowhere in the calculation.  And that assumes each system regenerates precisely when it needs to, which we already know single-tank softeners do not do.

Look, obviously you have your opinions; you’ve asked this question in several different ways on this and other forums.  There’s plenty of room for different softener designs in the market.  If you really want to test a twin-tank, counter-current softener that regenerates with treated water, why not install one in your home and see if you use less salt?

Dave, thank you for the detailed explanation. I really appreciate it. I asked the questions based on my interpretation of what I have been told about Kinetico specifically and other 'brands' of twin tank softeners. Here is a copy: " According to a Purolite (resin manufacturer) employee... regenerating resin with soft  water (as with a twin resin tank softener) does not decrease the hardness removal capacity of a volume of resin while regenerating resin with hard water (as with a single resin tank softener) does decrease the hardness removal capacity of that same volume of resin."

The employee is Gary Schreiber, possibly he may add a comment.

Yes I've asked this type of question before, and so far you are the only person that has answered it in any believable detail. Thanks again. As you see above, I am not alone in wanting the answers... I acknowledge I do not have anywhere near your technical knowledge (or Schreiber's), so I don't understand some of what you have just said and some of it goes beyond the scope of my questions but...

I was not comparing to packed bed design, just regular twin tank softeners (which I have sold for 20+ years). Also, you are working under a few other assumptions that are incorrect.

For a number of years I have been using a control valve that gives me metered immediate and metered delayed regeneration (when either is needed at any time of day ,or night). It is programmed for each. It does not require the programming of a reserve. It uses softened water for brine refill/makeup. Possibly you haven't heard of those abilities in a regular control valve before.

Fouling... As I said, I am not talking about iron or manganese removal capabilities and If these two different type softeners are installed on the same water, I expect both will suffer the same resin fouling/decrease in kinetics over the years. I'm sure you will agree with me that the vast majority of 'city' water does not have ferrous iron and/or manganese in it.

Osmonic shock. For 'city' water I size the regenerated capacity for a regeneration on average every 8 days with at least a minimum of 3333 gr/lb salt dose, and at times over 4k grs/lb.. I also get very good water use efficiency, in many instances comparable to your 9 gals once per day over the 8 day period that I size and program for. For well water I size according to what and how much of it is in the water and a very good salt efficiency with a different resin etc. and at times using a twin tank softener.

And the last point... (forgive any off topic self defense on my part) "only twin-tank systems can regenerate at any time without getting hard water to service." I agree, that is true. And yet 99% of my prospective softener customers tell me they  do not want to share their water flow with a softener being regenerated and that they don't, except very rarely like a toilet flush, use water during the 2:00 AM to 3:30 AM time frame when a regular softener regenerates. They also mention that they don't want the added expense and additional floor space requirement of a twin tank type softener.

Sorry, I do not understand what you mean when you say; "a system which regenerates only when necessary, i.e. one that has the ability to regenerate any day at any time is inherently more efficient (at least by a factor of 7/6 at 1 regeneration per week)."

Are you saying that a twin tank should be sized to regenerate once a week or that a twin being regenerated once or more frequently a day, is more efficient than a softener regenerating once per week? And more efficient in in what way; salt and/or water use?

I find many Kinetico twins regenerating once or more per day. IMO that should increase osmonic shock problems and increase friction wear on the resin beads.

Also, about the length of posts... I'm sure this type discussion is exactly what this forum was created for. Thanks Water Tech.

QUOTE>For a number of years I have been using a control valve that gives me metered immediate and metered delayed regeneration (when either is needed at any time of day ,or night). It is programmed for each. It does not require the programming of a reserve. It uses softened water for brine refill/makeup. Possibly you haven't heard of those abilities in a regular control valve before.<

Yes I am aware of this capability, and this gets to the heart of why this thread probably won’t get anywhere.  We both have different ideas of acceptable design criteria for a residential water softener.  One of my basic criteria is that the softener must not allow hard water to get into the customer’s supply.  Period.

By definition a true on-demand, single-tank softener like you describe will go into regeneration while someone is using water (that’s what triggers it).  The customer will get hard water when this occurs.  I don’t consider that an acceptable design/application because of my basic criteria.  One of my neighbors has a softener that works like this.  The raw water is 22 grains, the softener functions correctly, but there is 7 grain water throughout the house because it often regenerates while they are using hot water which contaminates the entire water heater.  You may find this acceptable based on your criteria; I don’t.

QUOTE>And yet 99% of my prospective softener customers tell me they do not want to share their water flow with a softener being regenerated…<

Here’s another example of different design criteria.  You don’t want your customers to “share” their water with the softener.  Apparently the softener you described initially is only for the remaining 1%.  :~)

This is not a criteria for me, although certainly the valve design must handle service and regeneration without pressure drop being an issue.  I’m not sure why your customers say that.  I can’t tell when my softener is in regeneration unless I am in the basement and hear water flowing to the drain.  I can tell when the well pump cycles, but not when the softener is in regeneration.

Certainly most modern-day softeners use valves with a large enough Cv so there is no appreciable pressure drop while regenerating. 

QUOTE> Sorry, I do not understand what you mean when you say; "a system which regenerates only when necessary, i.e. one that has the ability to regenerate any day at any time is inherently more efficient (at least by a factor of 7/6 at 1 regeneration per week)."<

Again, I’m assuming letting hard water get to the consumer is a very bad thing.  If you temporarily allow me that point, you can follow my reasoning.  For a single tank, “semi-demand” softener, the worst case is that it gets a trigger to regenerate at 6am in the morning during the first shower.  It now has to wait 20 hours to regenerate, so it must have that capacity left at the trigger point if it is going to still supply soft water for the rest of the day.  And that’s assuming the in-laws aren’t visiting and it’s not laundry day!  So assuming 1 regen/wk, that would be equal to one of the seven days [Now that I think about it, maybe my math wasn’t exactly correct, but you get the picture].  If you don’t care about hard water going to the customer, then I agree you don’t need any programmed reserve.

QUOTE> I find many Kinetico twins regenerating once or more per day. IMO that should increase osmonic [sic] shock problems and increase friction wear on the resin beads.<

Well I’m not sure about the “many” part.  There would have to be an awful lot of water used in that home on a regular basis; the vast majority of our gallon settings are much greater 250 gallons, which I would call the average household use per day.  But, you are correct that the inherent benefit of being able to regenerate at any time can become a liability if misapplied.  Resin that regenerates several times a day sees more osmotic shock.  However, that is way down on the list of important factors on resin life.  I’ve never heard of “friction wear” on resin beads being a cause of failure.  Resin can break apart, but that is from oxidation or osmotic shock, not from any friction forces.  BTW, one of our founders, Jim Kewley, just retired.  He had one of the original softeners in his house. Now that he is moving, we’re going to take it out and put it on display.  The softener is 36 years old with original resin and still producing 0 grain water.  We plan on testing the resin for capacity, moisture content, etc.  Want to place any bets?

Yes the thread is getting into 'marketing' rather than actual numbers but, that is OK with me. Our criteria is the same but my customer is willing to run the small rare risk of using water once every 8 days between 2 AM and 3:30 AM.

    QUOTE>By definition a true on-demand, single-tank softener like you describe will go into regeneration while someone is using water (that’s what triggers it). ... The customer will get hard water when this occurs. <

Actually that is not totally true with my softener, but it is true about all twin tank type softeners. Obviously you aren't aware of all the capabilities of the control valve I use... My softener waits to start a regeneration until no water use has occurred for ten minutes after the regeneration was triggered. That happens very rarely but, when it does, they get softened water for the first two hours after the trigger plus the ten minutes or more of water use. Then they get hard water if they use water during the next hour+ until it gets back to service.

    QUOTE> One of my neighbors has a softener that works like this.  The raw water is 22 grains, the softener functions correctly, but there is 7 grain water throughout the house because it often regenerates while they are using hot water which contaminates the entire water heater.  You may find this acceptable based on your criteria; I don’t. <

You aren't describing the softeners I sell. I'd say your neighbor's softener is not sized correctly or it's not set up correctly.  Possibly you could help him with that.

Actually, if the prospective customer has a 24 hr water use pattern, I sell them a twin tank softener. The other 99%, they go with the two tank I've described.

    QUOTE>This is not a criteria for me, although certainly the valve design must handle service and regeneration without pressure drop being an issue.  I’m not sure why your customers say that.  I can’t tell when my softener is in regeneration unless I am in the basement and hear water flowing to the drain.  I can tell when the well pump cycles, but not when the softener is in regeneration.

Certainly most modern-day softeners use valves with a large enough Cv so there is no appreciable pressure drop while regenerating.  <

Obviously their old softener is undersized for their peak demand flow rate, even with your Quad Drive valve and the 6" x 18 or 7" x 35" tanks. When one tank is regenerated, they say they feel the decrease in 'pressure', although they mean reduced flow.

MyQUOTE> Sorry, I do not understand what you mean when you say; "a system which regenerates only when necessary, i.e. one that has the ability to regenerate any day at any time is inherently more efficient (at least by a factor of 7/6 at 1 regeneration per week)."<

    QUOTE>Again, I’m assuming letting hard water get to the consumer is a very bad thing.  If you temporarily allow me that point, you can follow my reasoning.  For a single tank, “semi-demand” softener, the worst case is that it gets a trigger to regenerate at 6am in the morning during the first shower.  It now has to wait 20 hours to regenerate, so it must have that capacity left at the trigger point if it is going to still supply soft water for the rest of the day.  And that’s assuming the in-laws aren’t visiting and it’s not laundry day!  So assuming 1 regen/wk, that would be equal to one of the seven days [Now that I think about it, maybe my math wasn’t exactly correct, but you get the picture].  If you don’t care about hard water going to the customer, then I agree you don’t need any programmed reserve.<

My control valve has variable reserve, that's why I don't have to calculate one.

And in my experience, comparing one day's worth of reserve capacity and the salt used to regenerate it in a two tank type softener, to the grains used by all twin tanks to regenerate each tank every regeneration, usually once or more per day, the two tank will usually be more salt efficient. I.E. your 11 gallons of water and 1 lb of salt unit regenerating 2-4 times per day times 8 days will use more salt, and water than my two tank regenerating once every 8 days.  That I can do the math on...

MyQUOTE> I find many Kinetico twins regenerating once or more per day. IMO that should increase osmotic shock problems and increase friction wear on the resin beads.<

    QUOTE>Well I’m not sure about the “many” part.  There would have to be an awful lot of water used in that home on a regular basis; the vast majority of our gallon settings are much greater 250 gallons, which I would call the average household use per day.  But, you are correct that the inherent benefit of being able to regenerate at any time can become a liability if misapplied. <

I talk to 2-6 prospective customers per day 5-6 days per week; I also answer a few emails each day 7 days a week. I've been doing that for 5 years now and 2-5 per week tell me they have an old Kinetico softener or have had a proposal from Kinetico. The softeners have been undersized, or IMO, misapplied.

    QUOTE>Resin that regenerates several times a day sees more osmotic shock.  However, that is way down on the list of important factors on resin life.  I’ve never heard of “friction wear” on resin beads being a cause of failure.  Resin can break apart, but that is from oxidation or osmotic shock, not from any friction forces. <

Many years ago I was told that the use of a Turbulator distributor tube caused friction wear and I have always repeated that. I've also been told that resin wears out due to frequent regeneration. Logic says that friction wear should be a probability if for no other reason than resin beads are not as hard as rocks and I know if I rub them together they "wear". But maybe I'm wrong and it is not due to friction.