Match the Application
September 6, 2011
Electronic plumbing fittings are known to offer sanitary, touch-free operation, while conserving water and energy in that they only flush or dispense water when the sensor detects a user. Sensor-activated faucets can also regulate water delivery time. Once a facility decides to go with sensor-activated faucets and flush valves instead of manually operated models, the next choice is power type.
When the sensing technology was first introduced, battery-powered fittings were only used in building retrofits where it would either be impossible to hard wire the existing space or when a cost-effective addition of low-voltage power was not feasible. Hardwired, AC-powered systems are good for new construction or major re-construction projects where additional electrical service can be more readily run.
Today, however, good battery-powered systems are used as often as hard wired systems as they avoid the upfront cost of adding electrical wiring. They are also chosen when converting from a manual to electronic fitting. Further driving acceptance is the ever increasing battery life, which extends the service interval and lowers the total lifetime cost of the product.
Because there are many different types of batteries available, it is important to understand the advantages and disadvantages of each type so the right choice is made for the specific application. All batteries have a set capacity on which power is drawn from. High or low current needs, intermittent or steady drain, and temperature are all factors that impact battery longevity. In the case of plumbing fixtures, restrooms typically have low current, intermittent drain conditions. Temperature depends on the location (indoor versus plumbing in more exposed areas, such as a standalone restroom building in a park).
The most common type of primary battery is alkaline. It gets its name from its use of alkaline aqueous solutions as electrolytes-based on manganese dioxide, zinc and a caustic potassium hydroxide-zinc oxide electrolyte. The alkaline battery has a high energy density; long shelf life, which is typically seven years; and superior leakage resistance. Its lower internal resistance allows it to operate at high discharge rates over a wide temperature range.
Alkaline batteries have a high rated capacity and deliver their full capacity if the power is used slowly. Under normal, room temperature conditions, the battery will self-discharge at a rate of less than 2 percent (Duracell Ultra <1 percent @ room temperature) per year. However, if alkaline batteries are stored or used in higher temperatures, they will lose capacity more quickly. For example, at 85 degrees Fahrenheit, they lose about 5 percent per year; at 100 F, they lose 25 percent per year. Interestingly, if used in cooler climates, the capacity change is insignificant and really does not affect how long the battery will last. The shelf life is still seven years in environments below normal room temperature. Fortunately, most plumbing fixtures are installed in cooler places and make alkaline batteries a good choice.
A disadvantage of alkaline is the possibility leaks when it is normally discharged below 0.8 volts. To minimize that problem, some electronic fittings first warn the user of a "low battery" and then, after a number of additional activations (time period to replace the batteries), it shuts the power off when the battery voltage drops below a critical level-ensuring the fitting does not initiate water flow without enough power to end the cycle.
One of the advantages of alkaline batteries over other batteries is the relatively low toxicity of the ingredients. Therefore, alkaline batteries pose less of a challenge to the environment. Additionally, the cost and availability of alkaline batteries add to the convenience.
The lithium manganese dioxide (LiMnO2) or lithium primary battery is another good source of power for electronic plumbing fittings because they also provide excellent performance at low to medium current applications.
The major advantages of lithium manganese batteries over alkaline batteries are their good storage life and discharge performance. Operating temperatures have little effect on operating characteristics because the cell is very efficient. They also provide excellent performance at low temperatures. Because of lithium manganese oxide's stability and the fact that self discharge is so low, these batteries can be stored several years longer than alkaline batteries.
At a self-discharge rate of approximately 0.15 - 0.5 percent per year, these lithium batteries typically have a 10- to15-year shelf life and can last longer than alkaline batteries of the same size. However, because of the toxicity of the battery content, batteries cannot be easily disposed of and need to be recycled properly. There are instances when local municipalities should be connected regarding any disposal requirements.
As a side note, the lithium ion (rechargeable or secondary) battery is the fastest growing battery technology today. Lithium ion batteries are more sensitive to characteristics of the discharge current and can be unsafe when improperly used. Because they also pose hazardous waste issues due to their heavy metals content, they are not recommended for plumbing fittings.
Newer to this space is a 25-year battery application. Its chemistry is lithium thionyl chloride equipped with a patented hybrid layer capacitor that collects small electrical charges, which are discharged every time the faucet is activated. This allows the cell to maintain its power storage. Not all versions of this power system have a hybrid layer capacitor; the capacitor reduces the pulse height of intermittent drain, which reduces the life of the batteries. This hermetically sealed battery has a self-discharge rate of <1 percent per year.
This type of battery is not recyclable and needs to be returned to the manufacturer for proper disposal. The additional electronics required for this technology add an extra element of concern regarding reliability. Especially, with a rather high replacement cost and the need to purchase direct from the original equipment supplier. These are not an off the shelf solution available to the general consumer.
Which to Choose?
Keep in mind that battery shelf life and operating life are not the same. Getting the most out of them requires recognizing and tapping into their strengths and weaknesses. In essence, determining which type of battery to use depends on the application.
High-traffic areas, for example, consume many more batteries than a low-traffic restroom. Realistically, in the case of a high-traffic area, the benefits of using a battery with a longer shelf life may not pay off; using it only gives a few hours more of operating life and has a higher replacement cost. A low-traffic restroom, on the other hand, can take advantage of a battery with a longer shelf life.