Scaling down the cost of limescale

For years, the go-to solution for preventing limescale accumulation in building services systems has been the trusty salt-regenerated water softener. But as Facilities Managers become increasingly responsible for budgetary and environmental targets, in addition to operational duties, many are looking for solutions offering better credentials. Ian Barnes, Head of Sentinel Commercial, explains why scale no longer means softener, and how zinc anode based water treatment technology meets the needs of modern facilities and businesses.Around three-quarters of mainland England is served by hard or moderately hard water. The upshot is that only a relative minority of English commercial facilities are away from the clutches of limescale and its associated problems.

Limescale is a hard, chalky deposit which has the undesirable knack of accumulating in any untreated heating systems, especially ‘once through’ water heaters as these heat large quantities of fresh water. Here, the build up of limescale can severely impair operating efficiency.

British Water estimates that just 1.6mm of limescale accumulation can increase a heating system’s energy requirement by up to 12%. Why? Well, in effect limescale deposits act as insulation, drastically reducing the efficiency of heat transfer surfaces. The unfortunate outcome for facility managers is that boilers run hotter, for longer, consuming greater quantities of energy. Furthermore, when limescale is allowed to build up in pipework, the reduced diameter of the bore leads to restricted water flow, thus pumps must work harder to deliver the same volume of water. Ultimately, both energy consumption and system noise are increased, while extra stress on the pipework can easily cause leaks. Similarly, limescale also accumulates freely inside hot water cylinders, suppressing their ability to operate effectively.

The harsh reality is that limescale build-up reduces component life, affecting appliances such as showers, washing machines, water heaters and immersion heaters, all of which are readily found in commercial facilities. Neglecting water treatment can lead to breakdowns, downtime and costly repairs. Conversely, correct water treatment will help ensure equipment runs efficiently, for longer, cutting energy bills, carbon emissions and, possibly, even the facility’s CRC commitment.

For decades the most common and conventional method of negating the expensive and troublesome accumulation of limescale has been to install a salt-regenerated ion exchange water softener. Without doubt, this is a proven technology, but in the modern commercial world, systems which introduce elevated levels of sodium to the water (maximum limits exist for drinking water), use valuable water for frequent regeneration, and need routine maintenance, may not represent the optimum choice for many facilities.

There is a clear requirement for alternative water treatment solutions offering proven financial and environmental credentials. For facility managers in need of a pointer, addressing the issue at source using a physical water conditioner offers a permanent solution to preventing the formation of limescale. A zinc anode based electrolytic unit provides a suitable option for any facility requiring entire-system protection against limescale.

These devices work by introducing extremely small quantities of stable zinc into the water using an electrolytic process with zinc anode and copper cathode. This has two scale-preventing effects. Firstly, the zinc will hold much of the naturally occurring calcium carbonate in solution, minimising the formation of crystals. Secondly, any calcium carbonate crystals that do precipitate will develop as soft non-deposit forming aragonite, instead of hard deposit-forming calcite. Zinc technology systems require no salt, and operational costs are negligible.

Returning to traditional ion exchange softeners, no one doubts they work, because they do. However, by design, such systems need regular regeneration, typically daily, with salt addition required to restore resin capacity. It is possible to save thousands of pounds every year in salt bills alone by replacing a mid-sized commercial water softener of this type. In fact, changing to a zinc anode based electrolytic water conditioner is predicted to save £3,400 on salt a year for a typical commercial user. On top of this, there is the administrative procedure of sourcing, ordering and stocking salt, as well as keeping the system tank topped up: 25kg bags need to be lifted to waist height. Also, forgetting to add salt is a common pitfall.

And then there’s the issue of water. A medium-sized ion exchange softener can use up to 1,000 litres (1m³) of water per regeneration, depending on the system’s resin bed capacity. To give it some perspective, this equates to just over 1,750 pints of beer, 15 baths or 220 gallons of petrol. What’s worse, it ends up going straight down the drain. This water cannot be recycled or reused as grey water thanks to its high salt content, making ion exchange softeners both prohibitively expensive and environmentally unsustainable. Salt’s carbon footprint can be as large as 1 tonne of CO2 for every 4 tonnes used.

Any facility manager looking to replacing a mid-sized ion exchange softener with a zinc anode based electrolytic water conditioner can expect to save approximately £840 a year on water bills. Adding this to savings in salt and time means payback is normally achieved within 12 months.

Sure enough, there are alternatives to zinc anode based electrolytic water conditioners. The most common are magnetic water treatment products, which claim to use a magnetic field to change the properties of scale-producing minerals in the water. Another type of water conditioner is purely electronic-based and is commonly known as an electronic descaler. These claim to work by transmitting an audio frequency or radio frequency signal into the water via induction coils wrapped around the pipework. Alas there appears to be a general lack of readily available independent research regarding the performance of these alternative technologies, let alone any comprehensive details of their scale inhibiting mechanisms. As a result, any meaningful comparison to zinc-based technologies is not possible.

Zinc anode based electrolytic water treatment technology, as used in products such as KalGUARD, is independently proven, WRAS approved and the methodology is recommended in the Compliance Guide to Part L of the UK Building Regulations. These devices are typically fitted on a rising main, before the water storage tanks and booster, to treat all systems with the required quantity of zinc in relation to water flow. With this in mind, only one unit is needed. As the process does not induce decay on standing or agitation, limescale can be controlled wherever water is delivered.

Another significant advantage for facility managers is that everyday maintenance demands are considerably lower compared with brine regenerating softeners; in fact they are negligible as there is no requirement for regular water testing, lifting heavy bags of salt (possibly also a health and safety issue), or resin replacement. In contrast, a zinc anode can last approximately 8-10 years.

These reasons are why growing numbers of facility managers in various sectors are investing in zinc anode based electrolytic technology to protect their water systems; from manufacturers and warehouses, to office blocks and universities. Don’t miss out.

Hotel evicts unwanted guest: limescale

Faced with incoming mains water hardness levels of around 260ppm, a 120-room UK hotel in Banbury, recently took action to negate the high potential for limescale that is prevalent in its area. The hotel installed a zinc anode based electrolytic water treatment in March 2012 and has seen dramatic results in limescale reduction.

The hotel had a history of related problems within its water heaters. To counteract the issue, it had been paying for periodic acid cleaning to remove the continual accumulation of limescale – a costly and inconvenient exercise. With efficiency a key driver for the hotel chain, the facilities management team commenced a search for a better performing and more cost-effective solution – ideally one that would not only treat the system, but also prevent the reoccurrence of limescale. Research led to the KalGUARD water treatment system from Sentinel Commercial.

Water usage at the hotel is around 21m³ per day with a peak flow rate of 50 l/min. Here, the hotel’s water supply enters a CWS tank and is boosted to all hot and cold water services, including two water heaters. By installing zinc technology on the rising main, it was assured that limescale would be prevented from depositing inside the heaters, while simultaneously keeping other hot and cold outlets clean.

Following installation, the hotel’s maintenance service provider initiated an internal inspection of the water heater. Previously the heat exchange tubes would have been coated with limescale, however the examination revealed that, apart from some minor deposits of old scale that had spalled-off during a previous acid clean, the tubes were clear of limescale.

Summary of the facts

  • Hard water areas cover around 75% of England
  • 1.6mm of limescale accumulation can enhance a heating system’s energy requirement by up to 12%
  • A typical mid-sized commercial salt-regenerated water softener uses 920 litres of water per day: water which can't be recycled or reused due to high salt content
  • Salt for water softeners costs thousands of pounds every year
  • Water softener regeneration can take up to 90 minutes, and requires heavy bags of salt to be lifted by staff on a regular basis
  • Scientifically-proven zinc technology does not waste any water, it requires no salt and is WRAS approved
  • Payback is normally achieved in less than 12 months