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Has heating efficiency hit a stumbling block?

Achieving the best efficiencies from heating and hot water systems is only possible when components are free from sludge and limescale build up. Ian Barnes outlines the key considerations for cleaning and protecting heating systems, highlighting best practice in both areas.
It stands to reason that any heating or hot water system will work better, faster and more efficiently when the internal water is devoid of sludge and heat exchange surfaces are free from limescale. This applies to all commercial heating systems - regardless of size, specification and fuel type - whether traditional radiator-based, under-floor, boiler-fed, solar, thermal or direct-fired water heaters.

Ensuring that system water is clean, and making sure it remains so, is the best way to maintain overall system performance. In this regard, the two biggest concerns are iron oxides - black magnetite sludge and red rust deposits - and calcium carbonate deposits, commonly known as limescale. These two culprits affect heating systems differently, so understanding how is essential if water treatment is to be thorough and effective.

'Sludge' is symptomatic of untreated closed heating systems, and builds up in the boiler, pipes and radiators. It is comprised of around 95% magnetite, which is caused by the chemical interaction between metal and water, and its formation is accelerated by any air that may be in the system. Sludge build up lowers efficiency, causes cold spots in radiators, puts additional stress on pipework, increases system noise, and can even cause leaks.

Once corrosion has begun, it tends to be self-perpetuating, which is why a regular water treatment maintenance programme is so important.

Limescale affects untreated 'once through' water heaters and systems with continual water make-up, and is endemic to hard water areas - which unfortunately includes more than 65% of the UK. As limescale deposition is exacerbated when water is heated, the worst affected components are often the heating elements themselves. Aside from the functional benefits, water treatment is also advantageous with regard to reduced carbon footprint, which in turn equates to financial savings.

British Water research suggests that limescale accumulation of only 1.6mm can increase a heating system's energy requirement by as much as 12% - a figure which few can afford to ignore given today's high energy prices. In the longer term, financial returns relating to system life cycle costs are also available from correct water treatment.

This is because failure to prevent the accumulation of deposits within pipework, valves or heating elements can lead to the premature replacement of components (or even the entire system), resulting in additional expenditure.

What's more, since the narrow waterways found in commercial plate heat exchangers are prone to this problem, the accumulation of scale will result in lock-outs. The upshot is a direct risk to business continuity.

So what are the principal solutions with regard to cleaning and protecting building services systems? Well, there's a whole raft of water treatment solutions on the market - from flushing solutions for initial cleaning and liquid inhibitors designed to maintain permanent cleanliness in heating systems, through to conditioning technologies. Of course, employing the right solution for any particular commercial application is what's important.

Sure, it can be a minefield without the relevant expertise or knowledge, but many manufacturers have a technical department ready to offer advice and training wherever required. Despite this, there are general pointers and principles to follow.

With any new water treatment approach, it is always advisable to undertake a system flush beforehand, particularly if it has been operating previously without any form of protection. Failure to do so will mean the benefits of investment will be reduced due to the presence of debris.

The black iron oxide 'sludge' generated by system corrosion will distribute through pipework, affecting valves, pipes and boiler components such as pumps, seals, heat exchangers and diverter valves. There is simply little point in implementing any kind of corrosion or limescale protection unless the system itself is clean.

If selecting a liquid inhibitor - for a closed or vented heating system - it is advisable to choose one that includes more than one type of corrosion inhibitor to ensure protection for different types of metals. Inhibitors significantly slow the formation of new sludge, but may drop in concentration over time due to dilution.

As such it should be tested at least annually - self-testing is easy using a diagnostic system check kit - and topped up as required. Also, match the cleaning approach to the system requiring protection to ensure optimum results.

For instance, if the building was constructed in the 1800's, with the potential to compromise the integrity of ageing pipework, then a more subtle strategy may be preferable to that deployed in, say, new office buildings.

For water conditioning - for a direct fired water heater - where it is crucial to restrict long-term maintenance costs, or maybe treat both hot and cold supplies, then a zinc anode based technology - one that impels the precipitating calcium carbonate crystals to form as soft non-adherent aragonite instead of hard deposit-forming calcite - is advisable. In addition, because units of this type can be installed on a rising main, before the water storage tanks and booster sets, outlay is minimal in comparison with similar installations on bigger distribution pipes.

From a maintenance perspective, the only requirement with zinc-based systems is filter flushing approximately every six months, and field service contracts are available if desired, to ensure the unit is operating at optimum efficiency.

// The author is head of Sentinel Commercial //
14 August 2013

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