Water Softeners – It’s All in the Family
By Rick Andrew
Many of us are familiar with the concept of product families. This idea runs across many industries and product types and has common themes. Small-, medium- and large-size versions of a product is one example of how a product family can be developed and is probably the most common. This concept could apply to cookware, automobile tires, refrigerators, mattresses and more. The idea also could (and does) carry over to water softeners. It is common for manufacturers and/or dealers to offer various sizes of softeners for homes with various numbers of bedrooms and bathrooms (and buildings with different occupancies), with those softeners using certain common parts such as the same control valve, but different sized resin tanks with different amounts of resin. Taking this typical practice into account, NSF/ANSI 44 recognizes it and provides requirements to take advantage of it for purposes of conformity assessment.
What defines a family?
In general terms, what defines a family can be quite a deep question that can be a challenge to articulate or account for all the potential scenarios. But fortunately, when it comes to defining a family of water softeners, it is possible take advantage of industry practices and develop criteria that will be useful in most instances. These criteria for family definition are described in NSF/ANSI 44. The standard lays out criteria required to establish that a group of softeners is indeed a family:
• They use the same control valve.
• They use the same operating algorithm.
• They use the similar ion exchange resin.
• They use the same brine system.
• They use the same adjunct media (i.e., activated carbon, gravel, etc.), if any.
Individual softeners can vary in the following characteristics:
• They can use different size resin tanks.
• They can use different amounts of ion exchange resin.
• They can use different amounts of adjunct media, if any.
And there are the following limitations:
• The same type of salt is used.
• The resin tank cross-sectional areas of the softeners must be within certain limits.
• The cation exchange media bed depths of the softeners must be within certain limits.
• The bed depths of adjunct media or under-bedding must be within certain limits.
• The maximum service and intermittent flowrate of softeners per unit of cation exchange media volume must be within certain limits.
• The slowest rinse flowrates per unit of bed cross-sectional area for each softener must be within certain limits.
• The total rinse volume of water per cubic foot of cation exchange media for each softener must be within certain limits.
• The salt dosage per cubic foot of cation exchange media for each softener must be within certain limits.
• The cation exchange resin for each softener must be within certain limits for particle size, cross-linking and exchange capacity.
Looking at this list, it becomes clear that there are actually quite a few limitations regarding softeners being included in the same family under NSF/ANSI 44. Reflecting on all these limitations begs the question: what is the value of going through all of this to determine if a group of softeners are indeed a family under the standard? Why bother with families at all if we are required to deal with all these limitations?
The entire purpose of establishing a group of softeners as a family under NSF/ANSI 44 is to establish that a certain softener or softeners within the family can be used as test models to establish conformance to NSF/ANSI 44 of the other softeners in the family. So it may be possible to review the requirements and limitations and conclude, for example, that testing one softener of a family of five softeners will be sufficient to establish conformance and that the other four softeners don’t need to be tested. The ability to do this kind of family assessment and then ‘bracketing’ the softener models in that family with an established test model or models has tremendous value because it reduces the costs of conformity assessment, especially third-party certification.
When we think about this concept of families and establishing test models, it follows that there are specific limits on size ranges, design and operation to establish one or more softeners in the family as test models to qualify other softeners in the family. These specific limits on family bracketing and test models are as follows:
• The softener tank cross-sectional area is not more than 200 percent or less than 50 percent of the tested unit.
• The cation exchange media bed depth of softeners is not less than 75 percent of the bed depth of the tested unit.
• The bed depths of other adjunct media or under-bedding shall be 75 to 150 percent of that in the tested unit.
• The maximum service and intermittent flowrate of softeners per unit of cation exchange media volume is not more than 120 percent of that of the tested unit.
• The slowest rinse flowrate per unit of bed cross-sectional area is 50 to 120 percent of that of the tested unit.
• The total rinse volume of water per cubic foot of cation exchange media shall be at least 15 gallons (56 liters) or 90 percent (if less than 15 gal/ft3) of the rinse volume of water per cubic foot of cation exchange media in the tested unit.
• The total rinse volume of water per cubic foot of cation exchange media also shall not exceed 200 percent of the rinse volume of water per cubic foot of cation exchange media in the tested unit.
• The salt dosage per cubic foot of cation exchange media shall be within the range of the tested salt dosages per cubic foot of cation exchange media in the tested unit.
• The rated capacity per unit volume of cation exchange media at the same salt dosages shall not be increased.
• Comparable cation exchange media in mesh size and chemical formulation shall be within ± 10 percent of the particle size, crosslinking and exchange capacity of the cation exchange media used in the tested system.
Transferring test results within the family
According to these limitations, by establishing a family of softeners and a test model or models, we can assure that test results will be applicable across the family. As the test results are applied to non-tested models, NSF/ANSI 44 includes mathematical formulas that are utilized to calculate the softening capacity and, if applicable, the salt and water efficiency of the non-tested softener models in the family. For example, if a non-tested softener is larger and has 50 percent more cation exchange resin than the tested softener model, it would follow that the rated softening capacity would be increased by approximately 50 percent for the non-tested softener compared to the tested one.
To be as accurate as possible, however, the calculations do take into account the relative bed depths of ion exchange resin and the relative contact time (flowrates per cubic foot of cation exchange resin) of the two softeners. So, for example, if the non-tested softener has more shallow cation exchange resin bed and/or a lower contact time (higher flowrate per cubic foot of cation exchange resin), then the calculated softening capacity for the non-tested softener model with 50 percent more cation exchange resin is increased by less than 50 percent compared to the tested softener, according to the calculations specified in NSF/ANSI 44.
Leveraging family relationships
Many of us leverage family relationships. We may work in family businesses, we may benefit from the wisdom of our parents or we may call in our siblings for help with a project. These family relationships allow us to achieve more than we would otherwise be able to. Similarly, we can leverage family relationships when working toward conformity assessment of water softeners against NSF/ANS 44. By assessing groups of similar water softeners according to the criteria and limitations in the standard, we can establish families and representative test models. We can test a limited number of softeners and use calculations to establish conformance for the non-tested models. By doing this, we can accomplish more than we would otherwise be able to, just as we do with our own human families.
About the author
Rick Andrew is NSF’s Director of Global Business 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