BOILERS & HOT WATER Tackling limescale in commercial systems
Bill Sinclair, technical director, Adveco discusses how best to protect commercial electric hot water systems from limescale
A
s the electricity grid becomes cleaner and the potential for long-term carbon savings grows, commercial hot water systems in the UK are seeing an increased transition
towards electric-only designs. Through the application of simple to install, cost- effective, and familiar technology they deliver lower carbon emissions in line with government calls for Net Zero, address regulatory changes on new gas connections and remove NOₓ for improved indoor air quality (IAQ) and occupant comfort. However, there is also a growing realisation that this approach is suffering more acutely from the detrimental issue of rapid limescale generation in hard water areas. While an optimised electric-based system will be future-proofed through the incorporation of heat pump technology, electrical resistive heating remains a necessary component of many systems to deliver the high-grade heat required for domestic hot water (DHW) applications. Typically, the resistive heating is provided ‘directly’ to the hot water cylinder via an electrical immersion heater. Electric immersion heaters have been used for many years as backup heat sources in commercial boiler-fed indirect cylinders, a low-demand application for which they are perfectly suitable. However, with new Net Zero driving a preference for electric-only hot water systems, direct immersion heating is not advised as a primary heat source in hard water areas for commercial applications where delivering reliability is an essential business demand.
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Scale of the problem
Approximately 65% of the UK mains water is classed as ‘hard’ due to the presence of calcium. A naturally occurring mineral, calcium is safe to ingest so levels in drinking water are unregulated. In the cold water supply it is held as solute in the water and rarely leaves traces on the pipes and fittings. But when ‘hard’ water is heated the calcium precipitates out of the solvent as calcium carbonate, clumping together and attaching to the hottest surfaces as limescale. Within a water heater, limescale will typically form on the heat exchanger or heating element.
Variation in heat exchanger types impact the formation of scale. A direct electric immersion heater aggravates the formation of scale due to the temperature and intensity of the heating element, whereas a heat exchange coil or tube typically exhibits a much lower surface temperature and comparatively less scale formation. These larger heat exchangers also have a
greater capacity to expand and contract, causing scale to flake off as it forms, avoiding detriment to the heat exchanger. Electric immersion heaters with close, tight bundles of rods also expand and contract, but some scale
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