Dec 30, 2016

Alternative Corrosion Protection

Systems aid in scale control for tankless water heater systems

Many areas in the U.S. struggle with limescale corrosion, and modern water treatment using chloramines can compound the problem in copper pipe and boiler and tankless water heater heat exchangers. Commercial water softeners traditionally have been used to protect this equipment, and they often are recommended for limescale control where greater volumes of water are utilized. This protection is critical to eliminate breakdown and holes in the copper heat exchangers and other parts of the equipment.

Above image: Tankless water heaters, like those installed at this California apartment building, are susceptible to scaling and corrosion. 

Water softeners may have a higher up-front cost, require regular maintenance, and produce water waste through backwashing. Plumbing contractors looking for alternatives to water softeners sometimes have relied on smaller scale control systems designed for residential applications.

Commercial multi-tankless water heaters are now being specified for large-scale apartment buildings. These systems require finite treatment for optimum operating capabilities, and scale control systems have been introduced to help protect them from damages hard water can wreak. 

Case Study No. 1

A 29-unit apartment building in San Fernando, Calif., has five commercial condensing tankless water heaters in parallel feeding the hot water with a solar water heating system, which also is susceptible to scale and corrosion. The building implemented a system developed by United Filters Intl. designed to treat boiler and tankless water heater limescale corrosion utilizing stainless steel vessels, 5-µ polyester pleated sediment filters and Siliphos scale inhibitor media. This media has been used since the early 2000s as a cost-effective, low-maintenance, environmentally friendly option. Made of hexapolyphosphate and silica, it can withstand temperatures up to 170°F, making it ideal for the high temperatures of heat exchangers. The systems are modular, so they can be designed for up to 560 gal-per-minute (gpm) flow and 8-in. in and out ports utilizing multi-round filters. Maintenance is decreased, as these filters usually need replacing once a year (depending on water usage and hardness). Checking the system after six months is recommended.

In the San Fernando building, one five-round stainless steel vessel system with 2-in. in and out ports, equipped with five 2.5-by-20-in. polyester pleated sediment filters and Siliphos scale inhibitor media for an approximately 50-gpm flow rate was installed in the garage at the point of entry to the solar water heating system.

After one year, filters have been replaced and the system has effectively protected the tankless water heaters and solar water heating system against corrosion from limescale without compromising flow rate. There were no operating problems during this period. The tankless water heaters incur error messages in the case of heat exchanger corrosion.

Case Study No. 2

A 78-unit apartment building in Huntington Beach, Calif., has 14 commercial condensing tankless water heaters located in two areas on the roof. Two seven-round stainless steel vessel systems with 2-in. in and out ports, equipped with seven 2.5-by-20-in. polyester pleated sediment filters and Siliphos scale inhibitor media for an approximately 70-gpm flow rate were installed on the roof to accommodate each tankless heater rack system.

After one year, filters have been replaced and the systems have effectively protected the tankless water heaters against corrosion from lime-scale without compromising flow rate. 

Case Study No. 3

A hotel in Palm Springs, Calif., recently had a scale control system installed. It features 3-in. in and out ports, and the flow rate is approximately 150 gpm. The water in Palm Springs has significant hardness, and this system is being used to protect a boiler.

Although the savings have not yet been calculated, combining the decreased maintenance on an ongoing basis with the initial startup costs, the hotel will save thousands of dollars on a yearly basis, while also protecting its equipment from scaling and corrosion. 

About the author

Susan White is a freelance writer and marketing consultant for various water treatment professionals. White can be reached at [email protected].

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