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Examining the options to a high-scale problem

Stored hot water systems suffer badly from the problem of scale build up – even when water treatment measures are set in place which could put a burden on water heaters. Scott Humphries argues in favour of zinc-based calcium inhibitors

Lime scale consists of calcium carbonate (calcite) with lesser amounts of other calcium salts such as the sulphate. Sometimes limescale deposits contain corrosion debris and this scale build-up can affect the water heaters by reducing their efficiency and overall performance. Ultimately, ongoing use with hard water will shorten the lifespan of water heating appliances.

Limescale build up is a serious problem in Southern England, Wessex, Wales, Hull and the Thames area. In these hard water areas especially scaling in stored hot water systems ultimately leads to lower performance, breakdown, and expensive remedial treatment such as power flushing and in the worst scenario cracked cylinders. Serious money has to be then spent to get the system back to work; all of which means downtime, inconvenience and, for many businesses a detrimental impact on income.

Basically there are three types of water treatment available for the management of scale. The first, a calcium softener, physically takes calcium out of the water and exchanges it for sodium. The second type is a physical electromagnetic device that clips around pipe work and encourages the scale to ‘go with the flow’ rather than affix itself to the cylinder.

Sodium water softeners are effective but have two drawbacks – the water is not potable and they rely on people to put salt in them, thereby allowing a large margin for human error. One of the most common reasons for engineers to be called out is because ‘the water softener has stopped working’. Ninety nine times out of a hundred this is only because the operator has forgotten or omitted to add salt to the water conditioner. The third solution, zinc based calcium inhibitors, encourages generation of nucleation sites in the water that encourage scale to form but the resulting crystals are smaller so they stay in the water rather than adhering to the metal sides and thereby causing scale build-up.

The use of water softeners and scale inhibitors can go a long way towards alleviating the problem but with stored hot water systems, apart from calcium water softeners if, after passing through the conditioner, hot water is subsequently stored in a cylinder then after 24 hours the process is reversed and scale begins to build up again. On top of this, any serious turbulence can affect performance and scale up the heat exchanger – ie where there are tight bends in the system.

Continuous flow water systems are the easiest system to keep scale free. When quoting for big installations, for example, multiple showers and numerous wash hand basins – continuous flow systems save 30-35 per cent on install and around the same on gas costs. And there is no costly messing around with salt-based conditioners.

Even where a ‘turnkey pack’ system such as the Rinnai Infinity Plus Storage is fitted and a booster tank added the water is unlikely to be held for 24 hours. These systems are commonly used in hotels, for example, to deal with peak demand times and because these recover in minutes, scale is never likely to be a problem.

To be sure limescale is never a problem, Rinnai heaters also incorporate a scale warning device that continually monitors the appliances for limescale deposits around the heat exchanger. Once lime scale build up has being identified, a message is sent to the built-in interface panel on the front of the appliance to alert the end user that it is time to call a Rinnai service agent to perform a lime scale flush.

For a ‘belt and braces’ solution a continuous flow system, combined with zinc treatment means end users can virtually say goodbye to scaling. The process gives up zinc ions that stay in the flow for a longer conditioning cycle. For the sake of a small cash outlay, (as little as £200 depending on diameter of pipe), a zinc conditioner is a useful safeguard and one that will give end users additional peace of mind. Unlike calcium water softeners, zinc treatments only need attention every 2-3 years, which could be simply built into the maintenance contract, thereby keeping costs down.

// The author is a sales consultant for Rinnai //

8 July 2014

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