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Restaurant Virtually Eliminates Limescale With Electric Water Heating Application

Commercial hot water specialist Adveco has demonstrated how a restaurant virtually eliminates limescale from its hot water application to ensure business-critical daily operation. Adveco is working in partnership with a global restaurant brand to support the rollout of net zero restaurants demonstrating low-emission innovations throughout its chain of UK drive-through and high street franchises. Through the application of live metering, Adveco has demonstrated to the customer that servicing domestic hot water (DHW) water demands of between 1200-1500 litres per day could equate to as much as 20% of total energy usage within the organisation’s target net zero restaurants. One year ago, the refurbishment of a restaurant in the King’s Cross area of London provided an opportunity to address the emissions generated by this provision of hot water for the restaurant. In addition, working within existing building limits meant the application needed to maximise limited external and plant room space of this central London location. The location also previously had struggled with problems of limescale due to the hardness of the water supply, so creating an application which eliminates limescale was key. Working to an all-electric specification, Adveco designed an application that would harness its’ 9kW FPi32 air source heat pump (ASHP) for preheat with additional top-up heat supplied by an ARDENT P 12kW commercial electric boiler. These would supply thermal energy to a mains water-fed compact SST500 stainless steel twin-coil indirect cylinder. By combining ASHP and an electric boiler Adveco addressed many of the complexities associated with integrating ASHPs into the existing building. This combination enabled the system to be sized down, by as much as half in terms of ASHP requirements delivering immediate capital savings as electric boilers are far less expensive compared to an equivalent heat pump. It also immediately reduced the physical size of the system, embodied carbon and demand from the electric supply. Additionally, the system retains redundancy should there ever be a failure. Balancing a hybrid electric system is key to ensuring efficient operation. Adveco supplied the controls to ensure the water heating remained consistent, optimising the ASHP preheat and top-up from the boiler to reduce energy demands and the building’s emissions. The electric boiler operates at the same efficiency as an electric immersion heater (100%) and so the only overall difference in system efficiency is the minimal pump electrical consumption and a negligible amount of heat loss in the pipework. Although the system takes up a little more space than an all-in-one electric cylinder, it has more versatility. It requires less clearance for the cylinder, so it was compact enough to fit into the extremely limited space allowed for plant in the restaurant. The customer’s key concern was the system resilience, particularly with regards to damaging limescale build-up which is a serious and potentially expensive problem for commercial hot water systems installed in hard water areas. London is one area that particularly suffers from this issue, with unprotected commercial systems known to incur irreparable damage to immersions and cylinders. Adveco ran some initial tests at the location including use of a direct immersion. Immersions are designed for use as a secondary heat source preferably acting as an emergency back-up should there be a failure in the primary system, but we are seeing more specifications with them used as a primary heat source as buildings shift away from gas to electric as a low-carbon alternative. This is not recommended.
The difference between limescale build-up on the heater elements of an indirect electric water heating system vs a direct electric water heating system.
12 months of use of an indirect electric system versus one-month direct electric immersion test to demonstrate limescale deposition
On this occasion, the test immersion was used constantly for a week to supply heat. The high heat intensity of the immersion, even during this short period of time, demonstrated excessive levels of limescale deposition on the heating element. When limescale forms and remains on the heat transfer surface, because it is non-conductive, the surface becomes insulated leading to overheating of the element. Over time this will cause it to rupture if the heat cannot be dissipated. Under these monitored conditions the lifespan of the immersion was estimated to be a matter of months, yet their cost is not too dissimilar to that of the ARDENT electric boiler.

A move to electric that still eliminates limescale…

An advantage of incorporating the ARDENT electric boiler was that it heats water using an array of smaller immersion heaters located in a small tank within the boiler housing rather than directly installed into the hot water tank. This creates a sealed ‘primary’ loop to the indirect coil in the SST500 cylinder. The electric boiler heats the same water continuously so there is only a small, finite amount of scale in the system which will not damage the elements. The heat exchanger in the cylinder is a large coil operating at a relatively low (80°C) temperature. The intent was by controlling temperatures and employing an indirect method of water heating the system the common problems of destructive limescale build-up seen in direct immersion electric heating would be eliminated. One year on from the commissioning of the system, the first annual warranty servicing demonstrated the efficacy of this approach. Upon removal of the coil from the SST500 for inspection it was clear that limescale deposition had been minimised. What little limescale which had deposited on the coil surface over the year could be easily wiped from the surface, before placing back into the cylinder. With the cylinder forming significantly less scale, the restaurant has gained from vastly improved reliability while reducing maintenance demands, for both operational and maintenance savings on top of crucial emission reductions. Visit the Adveco restaurant resource for more guidance on delivering low carbon and renewables to help achieve net zero restaurants by 2050, or read our free brochure. Also read our handbook (PDF) for further information on the application of electric hot water that eliminates limescale.