IN FOCUS Stainless Steel Indirect Cylinders – The Foundation Of Sustainable DHW A


plant room-based hybrid approach, which separates heat sources from the water storage, remains the most cost-effective, proven method for obtaining low-carbon water heating in commercial buildings. These systems deploy renewable or low-carbon preheat, typically


provided by solar thermal and increasingly air source heat pumps (ASHP), combined with top- up electrical heating - although many existing properties do still take advantage of lower cost to operate gas connections - for their high temperature water heating. Such systems need to smartly blend these varied sources of water heating, ready to be distributed


to basins, sinks, showers and baths. The process of blending heat takes place in the indirect cylinder, which acts as a highly efficient ‘battery’ in the larger-scale domestic hot water (DHW) applications required by commercial buildings. The cylinder, or calorifier as it is also known, provides a readily available reservoir of hot water that addresses daily consistent and peak demands. It’s a crucial element of the system, combining lower temperature pre-heat and higher top-up heat


to achieve the necessary 65°C safe operating system temperatures. Filled with cold water, the large, insulated tank incorporates dual heat exchanger coils, which connect to the heat sources. As hot water circulates through the coils, it transfers heat to the surrounding water in the cylinder. System controls will manage this process to maximise the efficient operation of pre-heat and top-up heating. The system’s overall efficiency is also enhanced as the insulated cylinder minimises heat loss. The stored water stays hot for longer, which in turn reduces the need for frequent reheating. With reduced load placed on the heat sources, system energy demands and therefore carbon emissions and operational costs come down and operational lifespan increases. Available in a range of storage capacities, indirect cylinders can also be connected in parallel to further increase capacity for larger scale or high demand applications. For applications requiring consistently high hot water flow, additional capacity becomes an absolute necessity for low-carbon applications based on ASHPs. The increased specification of heat pumps, especially in new build, has notably driven a resurgence in undersized system storage, especially in like-for-like replacement of gas water heating, as larger thermal storage is now required to offset slower reheating provided by ASHPs after periods of peak demand. Modern commercial buildings will also utilise unvented hot water systems, operating at mains


pressure, to deliver high-powered hot water flow necessary for large-scale applications such as showers, laundry, and dishwashing. One of the major issues faced by UK businesses using unvented hot water applications is the damage caused by the passage of mains water. In harder water areas, this is typified by the creation of limescale. In very hard water areas, this has seen high heat intensity immersion-based direct water heaters scale up and become unusable in a matter of months. This has massive implications in terms of ongoing maintenance and replacement costs. Because the indirect cylinder employs heat-exchangers, the water that is heated, especially by the higher-temperature top-up sources, circulates in a sealed ‘primary’ loop that never actively mixes with the mains water, which will pass around the wider system. With the boiler heating 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. By controlling temperatures through the indirect method of water heating, limescale build-up can be essentially eliminated.


Soft water can be equally destructive, unless stainless steel indirect cylinders are employed. These


boast exceptional resistance to soft water corrosion. When exposed to mains water, the metal forms a passive film of chromium oxide, which acts as a robust barrier, shielding the underlying metal from further corrosion. This inherent resistance to corrosion and the strength of the alloy make it ideal for unvented systems, which necessitate cylinders that can withstand significantly higher pressures. Stainless steel ensures safe and reliable operation, which translates to a longer lifespan for the cylinder, minimising replacement costs and downtime associated with failing equipment. The alloy’s smooth, non-porous surface also inhibits the growth of bacteria and other microorganisms. In commercial settings, hygiene is paramount, making stainless steel indirect cylinders particularly critical for hot water systems used in hospitals, hotels, and food service establishments. The preferred use of stainless steel, larger capacity tank and dual heat exchanger does mean indirect cylinders for low-carbon commercial DHW does result in a higher initial upfront cost compared to direct traditional heating systems. That expense is more than recovered over the extended lifespan of the system, with more simplified and reduced maintenance demands. Crucially, using a dual-coil indirect cylinder helps address many of the current complexities faced when integrating ASHPs, especially into existing buildings. They can also allow for later integration if a business has a more stepped approach to rolling out sustainability through the incorporation of ASHP or solar thermal at a later date. The ability to combine a stainless steel indirect cylinder with both ASHP and boiler, particularly the


compact electric variety, also enables DHW systems to be sized down by as much as half in terms of ASHP requirements. This delivers immediate capital savings as electric boilers are far less expensive compared to an equivalent heat pump, which helps offset the initial costs of the cylinder. Adveco offers the widest choice of commercial indirect hot water cylinders in the UK, and is an award- winning supplier of low-carbon hybrid DHW systems that deliver true advantage from the integration of these cylinders.


www.adveco.co Ability Case Study: JJ Mack Building


H1 - Ability fan coil units specified at JJ Mack - the UK’s first BREEAM ‘Outstanding’ commercial building


Fan coil units by Ability helped overcome the challenges posed by restricted ceiling spaces and an open-to-view design at the JJ Mack building at 33 Charterhouse Street, delivering the required cooling loads to keep occupants comfortable. JJ Mack, whose building takes its name from the original JJ Mack & Sons grocery store located on the site, became the


first commercial building in the UK to achieve a BREEAM ‘Outstanding’ rating. Inspired by its heritage, the distinctive design features of the impressive JJ Mack building blend the


past with the present. Market leading technologies were chosen to minimise the carbon impact of the building. After an independent sustainability evaluation by the Building Research Establishment (BRE), JJ Mack became the UK’s first building to be assessed as BREEAM Outstanding (2018). It also achieved an EPC rating of ‘A’, and that standard is only met by 1.8% of London’s non-domestic properties. At the design stage, the embodied carbon figure of 816 kg CO2e per m2 is 15% lower than the London Energy Transformation Initiative (LETI) current average design target. The operational carbon emissions were expected to be nearly 53% lower than the regulated Target Emissions Rate defined in Part L 2013. These sustainability credentials could only be realised by the careful specification of materials and construction processes chosen specifically to minimise carbon impact. Consulting engineers, Long and Partners and SES, the M&E contractor, chose Ability’s EVO range of


fan coil units to meet the exacting design and sustainability requirements, whilst providing the heating and cooling loads for the 200,000 square feet of office space. Andre Jonker, Associate Director, L&PO Group adds “We selected Ability’s EVO range because it is a


great product that sets itself apart in the industry with design flexibility and performance capabilities. We were pleased with the outstanding aftercare service the Ability design team offered during the specification process.”


H2 - What were the challenges to be overcome when specifying fan coil units? In line with the desire to reflect the building's heritage in the design, the JJ Mack building features a warehouse-style ceiling with criss-crossing exposed beams.


To fit in with the design and performance aspirations, the client required fan coil units that were: • • • •


Exposed to view in line with other building services in the ceiling space. Able to fit within the space between the ceiling beams.


Designed to meet the acoustic requirements of the office environment.


Able to provide the cooling and heating loads required in an energy efficient manner to match the sustainability focus of the project.


To achieve the efficiency required, integrated controls were key. Ability helped specify the controls with L&P Group. The design was centred around the layout and the requirements for the building and its usage.


H2 - Why were Ability fan coil units chosen for the project? The specifiers, L&P Group, working with the specialist sub-contractor SES, chose Ability to supply fan coil units for the project due to Ability’s wide-ranging industry expertise and product portfolio. Andre explains further, “A holistically designed solution was key to achieving the desired energy and efficiency ratings and in Ability, we found a partner that worked with us closely and offered support throughout the design process of the solution, as well as support with the unique design of the controls for this project.” The cooling load, size limitations and acoustic requirements for the office space all needed to be met


if the proposed solution was to meet the challenges posed by the project. Ability evaluated the dimensions of the exposed fan coil units required to meet the cooling load. The


preferred option was not viable because of the restricted space between the beams. A smaller fan coil that would fit between the beams was therefore proposed. The offices would have one fan coil unit every 6m to serve a space up to 4.5m deep in the perimeter zone, whilst one fan coil unit would serve 50 to 70m2 in the internal zone. The smaller fan units would be able to run at a lower power level, utilising variable air volume, and still supply the cooling loads required. Acoustics Consultant Sandy Brown’s report on the required office sound power levels confirmed that the smaller, exposed fan coil units did not compromise the required acoustic comfort requirements. Their average reduced power load delivered energy saving advantages, lowering operational and embedded carbon, matching the sustainability ambitions of this prestigious building. Troy Chambers, Head of National Sales at Ability, adds, “After assessing the cooling loads and acoustic


requirements, we were able to select the best fan coil from our extensive range to meet both the design and performance brief of the client and help deliver a truly outstanding and sustainable building.” This resonates with Andre, “I am truly pleased with this project. The JJ Mack Building to date is


one of the UK’s smartest and most sustainable office buildings. The building deservedly won ‘Project Design of the Year’ at the London Construction Awards 2023. Ability Projects played a big role in the design of the HVAC solution that utilises the EVO range of fan coil units, and their support has been outstanding throughout.” If you would like to find out how the Ability range of fan coil units could help meet the cooling and heating demands of your project, please contact one of our experienced team for advice and guidance.


www.abilityprojects.com Read the latest at: www.bsee.co.uk BUILDING SERVICES & ENVIRONMENTAL ENGINEER NOVEMBER 2025 35


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