Limescale protection numbers add up for commercial systems

Limescale within commercial heating and hot water systems is a common problem associated with hardwater areas. About 60% of mains water supplied in the UK is classified as ‘hard’ and this produces limescale deposits that reduce the efficiency of heating and water-heating appliances and systems. This means increased operating costs, as just 1.6mm of scale can reduce system efficiency by 12%, in turn increasing the amount of energy needed to meet hot water demands.

Limescale increases the energy consumed as it impedes the heat transfer efficiency of plate heat exchangers, water heaters, and other technologies, therefore, forcing this technology to input more energy to retain the same level of performance.

Just recently the Rinnai Technical Dept made a collective Case Study of three hotels: a small three-star hotel with 25 rooms; a medium hotel with 75 rooms; and a large hotel with 150 rooms. To conduct this study a gas system was sized for each archetype. The systems modeled for the sites are: 

• Small hotel - 2 x N1600 + 300L storage 

• Medium hotel - 6 x N1600 + 800L storage 

• Large hotel - 16 x N1600 + 2000L storage. 

The purpose of comparing different sized hotels is to show how the expected OPEX and carbon production savings increase as the size of the commercial building increases. This shows that scale protection is important for every system in a hard water area, and that the importance of this protection increases as the system size and hot water demand increases.

For the small hotel, for example, measured over a 10-year period as the thickness of scale increases from having no limescale to having 4mm of limescale results in showing that for every mm increase in limescale, the carbon production increases by 14,978kgCO₂. Therefore, if scale increased to 4mm, the system would produce an additional 59,912kgCO₂ compared to a fully protected system.

The output is similar from an operating costs perspective. For every mm increase in scale thickness, the operating cost to run the DHW system increases by £3,200. If the scale thickness increases to 4mm, the increase in costs becomes £12,799 over a 10-year forecast period – a percentage increase of 28%

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