COMMERCIAL HEATING T


hese 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-


32 November 2025


www.heatingandventilating.net


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, says heating specialist Adveco


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 a wide choice of commercial


indirect hot water cylinders and is an award- winning supplier of low-carbon hybrid DHW systems that deliver true advantage from the integration of these cylinders.


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