GO read some of our old posts where I have already explained this, or show up at the WQA show in Florida, I may be putting on a training seminar there. Or I have a large and free training seminar I am putting on in May in Texas, California in June, Florida in July, and a couple more still to be scheduled later this year. Send me a PM and I will give you the dates and times.
Or read below, but I as I have said earlier, this is a long one that will not be understood by you so why am I bothering, you will disagree with it no matter what I or anyone else write.
A twin alternating softener will give 24/7 100% system efficiency. The softener is also soft water regenerated allowing for the water used during the regeneration to be offset in the higher capacity of the regenerated tank. A single tank system will have a "reserve" capacity either manually added or algorithmically controlled by modern electronics. This reserve is lost capacity. Extending system regenerations to not more than every 7 days will minimize this lost capacity. Anything beyond 7 days and the efficiency gains become minimal but not incalculable. Twin alternating systems are designed to use 100% of their rated capacity prior to regenerating so no reserves are calculated into the system. Maximum flow rates need to be calculated with the regeneration backwash and fast rinse flows taken into consideration. A systems total available flow can be slightly lower due to this. A common system size of 10x54 may have a system peak flow of 18 GPM, this will be reduced to approximately 15.6 gpm since 2.4 gpm is used for the backwash cycles. The brine and rinse cycle is less than .75 GPM and therefore is rarely a concern. Some people have tried to falsely claim that the twin alternating systems use soft water during the regeneration and therefore the capacity needs to be calculated. This is a common misconception from people who do not understand the basics of water treatment. When have you ever calculated a systems capacity, and then took off the final rinse water from the systems capacity? This is actually done on some TDS compensated charts that many of the commercial companies use for larger capacity systems where even slight losses of efficiency can add up to a significant cost increase. Rarely does a residential application need to be so carefully controlled since the systems are usually slightly compensated during programming anyways and the very slight loss of efficiency adds up to less than a bag of salt per year or approximately $6. A twin alternating unit is ideal in a residential application where extremely hard water conditions occur or excessive water usage causes the regeneration to be more often than every 4 days. Very large single tanks can be used to extend regeneration frequency but channeling of the resin becomes a genuine concern for systems that will rarely exceed the systems recommended minimum flow rates. An example of this is a 14" diameter softener has a minimum recommended flow rate of 4+ GPM. If you rarely exceed that rate, you can start to have channeling problems. Also the cost of excessively large equipment can easily exceed the cost of a reasonably sized twin alternating system.
As to water efficiency, the amount of water used should be proportional to the size of the system and the amount of resin. So a twin alternating unit may regenerate daily, but will use the same amount of water (or less due to the lack of lost capacities based on reserves) as a very large system regenerating every third day.
Simple math: Application, 8 people, approximately 70 grains hardness.
twin alternating system regenerating every day 1.5 cu. ft. per tank, no reserve, 2.4 x 10 = 24 gallons backwash, 60 x .25 brine cycle (excluding brine)= 15 gallons, 2.4 x 10 fast rinse 24 gallons, brine fill 4 gallons, total of 62 gallons, annual salt usage 4380 pounds of salt, water usage of 22690 gallons
Single tank, 4 cu. ft regenerating every other day, 25% lost due to reserve. 7x10 backwash = 70 gallons. brine and rinse 60x.75 = 45 gallons, 7x10 fast rinse = 70 gallons, brine fill 11 gallons, total 192 gallons. Annual salt usage 5840 pounds, water usage 35040. This is a typical application
Here is an great short explanation of a twin alternating from this article.
http://www.wqpmag.com/search-softener-efficiency
Twin Alternating Systems
Twin alternating systems maintain one unit in service with the other tank in regeneration or standby mode. They are commonly used in applications that require 24/7 soft water. With the ability to regenerate multiple times in a day, they can be used in high-capacity applications with limited space availability. As an immediate regeneration system, the full capacity of each tank is used prior to regeneration. Upfront cost will be higher than a single unit, but the salt and water savings generally take a short time to pay for the increased equipment costs.
Residential applications can obtain the same benefits using a twin alternating system, though a very slight periodic service flow loss may be experienced as some of the incoming water is dedicated to the regeneration process.
Alternating systems can be expanded to include four or more tanks with enhanced capability and productivity. For example, demand-flow initiation is excellent for fluctuating service flow requirements as the number of tanks brought on line is determined by the real-time water demand.
Now all this being said, it can all be considered a non issue if variable brining were a common option, but that too has several minor problems that we can discuss during one of my training seminars. And, if anyone on this site wants me to host a training seminar, I will be offering paid and free training starting mid year, I will post more details when we are ready to launch this program.
Here are a few more writings:
Series 9100 Twin Water Softener
The Series 9100 Twin truly is the ultimate in water softener efficiency. The alternating twin tank design allows you continuous soft water 24 hours a day 7 days a week uninterrupted. And because each tank is used to its full capacity, there is no need for reserve, adding even more efficiency.
Easy
There is no timer to set.
High Flow
Every 9100 Twin is built with full flow 1" valves and distributors. Comes with a choice of either ¾" or 1" pipe connections, and an optional 1" commercial meter that increases flow rates up to 24 GPM.
Water Consumption
Adjustable cycle times allow minimal water usage.
Built-in By-Pass
An optional single lever by-pass valve allows an easy way to bypass the system and provides a simple disconnect.
Reliable
The five cycle 9100 Twin Series valve is motor driven - no solenoids or diaphragms to stick or hang up. This is the most reliable system for consistent performance.
Separate Salt Tank
The separate salt tank design protects controls from the harsh effects of salt and water that attack conventional control systems.
Flexibility
Due to the twin tank design, the 9100 Twin Series is versatile enough for tough residential applications, as well as for small commercial applications. Choice of salt tank sizes to fit most any space requirements.
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Solve your water problems with the “ULTIMATE TWIN” fully automatic softener.
Only an alternating twin tank system such as KRUDICO’S ULTIMATE models can ensure continuous soft water twenty-four hours a day-everyday. Salt and regeneration water are used only in direct proportion to the water that has been conditioned, giving minimum operation costs. Saves on soap, keeps fixtures and tableware shining and spotless, prevents scale build-up which can cause clogging in pipes.
On a twin system, the softener switches tanks then immediately regenerates the tank it just took offline. This allows the system to run each tank all the way to full capacity before switchover. In a single tank system, you must have enough remaining capacity to make it through a full day of the water softener has to regenerate the night before. If you are using a water softener as pre-treatment for a reverse osmosis system a twin alternating model is online 24 hours a day and therefore eliminates the need for pre-treatment lockout on regeneration
In my 25 years you are the only person who I recall that has ever tried to claim a single tank softener uses less salt and water than a twin alternating. This is why training, certifications, licensing etc is so important, otherwise anyone with an internet connection can make false and misleading claims. Now if you want to say that a twin alternating system is overkill compared to the potential salt and water savings in most residential applications I will heartily agree with you. But in those applications where regeneration frequency starts to get to the 4 or less days between regenerations without going to excessively large equipment, a twin alternating system should be considered. Why else do you think that the vast majority of commercial systems are now twin, tri, or quad system designs. The days of the single tank large commercial units are basically gone. I only stock a few HWBP 2900 and 3900 valve, the vast majority of our valves in stock are set up for twin to quad applications with NHWBP lower pistons.
I cant wait to see your response, with 50 quotes taken out of context, and you making a silly point that makes no sense, but I am expecting it so like I said earlier, you ignorance rarely surprises me anymore.