Water Conditioning & Purification Magazine

An Opportunity to Improve Capacity and Efficiency Testing of Cation Exchange Water Softeners

By Rick Andrew

NSF/ANSI 44 has long been the American national standard for residential POE cation exchange water softeners. It is a comprehensive standard, requiring evaluation of many aspects of a water softener to establish conformance:
Safety of materials in contact with drinking water

•    Achieved through review of formulations of materials in contact with drinking water, extraction testing and toxicological assessment of the results
Structural integrity
•    Achieved through testing water softeners for resistance to cyclic pressure and hydrostatic pressure
Pressure drop
•    Confirms that the softener will not cause a drop of more than 15 psi in line pressure when operated at the manufacturer’s rated service flow, which must be at least four gpm
Softening capacity
•    Establishes the amount of soft water a system can provide at manufacturer specified salt dosages
Rinse effectiveness
•    Confirms that the regeneration cycle of the softener is sufficient to prevent excess chloride from entering the softened water
Softening performance
•    Confirms that the softener can produce soft water for a minimum of 10 minutes when operated at the rated service flow
Accuracy of the brine system
•    Establishes that softeners set to regenerate with a specific amount of salt do so accurately
•    Although not required for conformance, the standard includes optional criteria to evaluate efficiency of demand-initiated regeneration type softeners.
•    The criteria are based on efficient use of salt and water compared to the amount of hardness removed after regeneration at specific salt dosages
Conformance by calculation
•    Establishes certification for non-tested softeners using the same control valve as the tested model and also falling within limitations for other criteria, such as resin bed depths, tank diameters, etc.
Product literature
•    Helps assure that installers and consumers have adequate information to understand the installation, operation and maintenance requirements for the system, as well as its capabilities and limitations

When considering this list, it is obvious that NSF/ANSI 44 is indeed very comprehensive. With a standard of this depth and breadth, one might wonder what, if anything, could be done to improve it. The truth is, like almost anything, there are opportunities to improve it. And fortunately, there are efforts underway to do just that.

Opportunity for improvement

The largest opportunity for improvement is actually related to technological advances in cation exchange water softeners. Over the last 10 to 15 years, a number of manufacturers of these systems have focused on developing and utilizing sophisticated electronic algorithms to achieve optimal system efficiency. Although these algorithms are typically proprietary and vary from manufacturer to manufacturer, what they typically have in common is the use of a flowmeter in the system and electronic data capturing to monitor water usage within the household. This monitoring may continue for a period of days or weeks. The algorithm then crunches the data to develop and implement customized, evolving and variable regeneration in an attempt to optimize efficiency in terms of salt usage, water usage and/or continually providing soft water for the user. The amount of salt, amount of water and frequency of the regeneration is determined by the electronic algorithm and can be changed by the algorithm over time as water usage patterns within the house change. So, what is it about this type of technological advancement that presents an opportunity to improve NSF/ANSI 44? In order to fully understand this, it is necessary to understand the current approach to capacity testing in the standard.

Capacity testing

Softener capacity is determined by testing at one half of the manufacturer’s rated service flow using a feed water with a hardness of 20 ± 2 grains per gallon. NSF/ANSI 44 currently requires capacity testing at the lowest and highest salt dosage settings specified by the manufacturer and the setting closest to the midpoint of the range of salt dosages. Capacity for other non-tested salt dosage settings is interpolated from the three measured capacities. Extrapolation is not allowed, so testing at the manufacturer’s lowest and highest specified salt dosages is critical. Each test of capacity is conducted by first regenerating with a precisely measured amount of saturated brine. The softener’s brine system is not utilized due to potential variation in the amount of regenerant salt. The end point of the test is defined as one-grain-per-gallon hardness breakthrough in the softened water. The hardness leakage throughout the test is calculated and subtracted from the total capacity introduced to the softener during the test, so the reported capacity is quite accurate. Three successive test runs must be within 10 percent of the average of the three test runs, with the average value being considered the official capacity at that salt dosage.

Back to the opportunity

Clearly, this method of determining capacity is based on the concept of softener system operation with user-programmed salt dosage settings. Although these systems may incorporate demand-initiated regeneration resulting in a varying number of days between regenerations, they always regenerate with the same set amount of salt unless the user changes the setting. With this mode of operation, the capacity test method described above makes perfect sense because it is based on programmed salt settings. With systems incorporating electronic algorithms, however, the user does not select or program a specific salt setting. And different salt settings may be selected and implemented by the system at different times depending on water usage patterns. Considering this mode of operation, the idea of testing and reporting softening capacity based on specific salt settings does not relate very closely to real-world operation or results. This is where the opportunity for improvement comes in.

Action being taken

WQA, NSF and a number of manufacturers have been working together on a task force to consider and address this opportunity. It is a fairly complex issue to consider, because a number of different aspects of testing and evaluation of softeners are affected by it. In addition to softening capacity, there are considerations with softening performance (the ability to consistently deliver soft water), softening efficiency for usage of salt and water, conformance by calculation for non-tested softener models and issues of consistent reporting of results and softener capabilities and limitations for users, so that apples-to-apples type comparisons are facilitated.

The group has been working on an approach based on real-world studies that have provided data regarding water usage by households with various numbers of family members. This approach will consider variability in the usage pattern and evaluation over a period of time. Although the details have not yet been fully worked out and the test method not yet fully developed (in fact, there is a considerable amount of work remaining), the result will be a standard that addresses the current most sophisticated technology. And the group is working to develop a standard that will do so in a way that is fair to manufacturers, implementable by testing laboratories and certification bodies and beneficial to consumers seeking to confirm manufacturer claims and make the most educated purchase decision possible. Achieving this result will mean that an opportunity for improvement will have been taken advantage of in the best possible way.

About the author

Rick Andrew is NSF’s Director of Global Busi- ness Development – Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: Andrew@nsf.org

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