Hybrid Hot Water Systems for Lower Carbon

The drive to bring greater sustainability into commercial and public sector buildings has never been more urgent, yet the consistent need for heat, in particular, to meet hot water demands cannot be avoided. Reducing carbon from what is typically classed as a business-critical service, especially in the wake of COVID and the drive to enhance hygiene, is certainly achievable with hybrid hot water systems. However, technical challenges remain, and inherent cost implications need to be overcome when reducing a building’s energy demands. This is especially true of small to medium scale operations, typified by offices, GP surgeries, cafes and restaurants and smaller schools.

Achieving 60°C in a calorifier is a basic requirement for a commercial domestic hot water (DHW) system. But achieving this through a direct electric-only immersion system is costly, even when compared to current surging gas prices. For this reason, air source heat pumps (ASHPs) would appear to be a perfect alternative, supplying low carbon heat to the building, and it is clear why the Government has championed the technology as a key ingredient in forging a path to net zero.

Heat Pumps and Commercial Hot Water

However, with ASHPs offering greater efficiencies in low-temperature systems, the high-temperature demands of commercial applications prove especially challenging. High working flow temperature from the ASHP would need to be at least 65°C, but to achieve this requires greater compression of the refrigerant, requiring more electrical input which results in a lower Coefficient of Performance (COP), in other words, efficiency is lost. As well as struggling to achieve these temperatures year-round in the UK, the very low drop in COP effectively counteracts the value gained from deploying ASHP.

A working flow of 50°C is however attainable all year round from an ASHP. If employed as a source for a preheat, the heat pump can be used to offset the direct electric costs of top-up after heat. Therefore, commercial new builds and refurbishment where gas is no longer being specified, are defaulting to this hybrid option.

Nonetheless, there remain a series of challenges. Aside from the additional system complexity, when connected to a traditional indirect water heater the lower flow temperatures generated by an ASHP lead to around a 50% drop in energy transfer compared to traditional gas-fired boilers. The size of the coil in the indirect calorifier can additionally limit heat transfer and affect system capacity. But for all-electric hybrid systems by far the most common problem comes from how the calorifier’s coil and the immersion interact.

An efficient electric hybrid hot water approach depends on harmoniously balancing these different system elements to ensure that they do not work against each other. If the coil and immersion are too closely situated, they become impossible to accurately control resulting in a steep drop in system efficiency. To avoid these issues, a hybrid hot water system would, up until now, be best served by employing a plate heat exchanger (PHE) with low-temperature hot water (LTHW) and domestic hot water (DHW) buffers alongside the ASHP. That of course further exacerbates the system complexity, space requirements and capital costs. For smaller to mid-scale hot water applications those capital costs can be hard to justify, forcing them, if possible, to be written off against sustainability gains.

Hybrid Hot Water Systems Designed for Commercial Buildings

In response, Adveco has been working in close cooperation with its customers to address the core challenges of delivering hybrid all-electric hot water heating into light commercial-scale building projects using ASHP technology. Evolving from bespoke system builds to award-winning packaged plant room applications, it became apparent that there is a growing demand for lower carbon pre-sized systems that are easy to specify, straightforward to install, resilient and cost-effective. This work has led to the creation of Adveco’s FUSION FPH-S range of all-electric, packaged hybrid hot water systems.

FUSION harnesses the highly respected FPi32 ASHP, a high-pressure ATSH calorifier with electric immersion, controls, and metering. Working together, this provides a reliable, high-temperature, sustainable and cost-effective system for meeting typical continuous hot water demands (from 257 up to 377 litres/hour) found in new commercial builds as well as refurbishment projects where gas and associated flueing is either not possible or no longer desired.

The system specification is available in 16 variants with 6 or 10 kW ASHP preheat and 9 or 12 kW electric immersion top-up.  Capacities ranging from 200 to 500 litres all rated at 10 BAR for high-pressure applications. This makes FUSION highly adaptable for a wide range of applications typically seen in public sector buildings. The FPi32 ASHP is specified to supply the preheated hot water throughout the year, even when ambient air temperatures drop as low as -25°C. The stainless steel construction of the ATSH also makes it an excellent all-rounder, resistant to soft water corrosion and, with Adveco’s own low heat intensity electric immersion specification (6W/cm2) the calorifier is more resistant to scale build-up in hard water areas.

FUSION ensures the ASHP preheat and immersion within the ATSH work seamlessly to deliver the highest operational efficiencies. Physical design spaces apart the low-situated high-efficiency preheat coil from the electric top-up immersion. Then dedicated controls and integrated metering monitor temperature and water flow throughout the system. This enables FUSION to make the greatest gains possible from the heat pump even though ambient temperature and system demands will fluctuate. These gains are then used to offset as much of the direct electrical top-up as possible, providing 53% carbon emissions savings (compared to equivalent direct electric only systems) and helping control the operational costs of providing business-critical hot water.

And without the need for a PHE or additional buffer tank, the capital costs of a hybrid hot water system become more manageable while making major gains in terms of space-saving. Something often identified by customers as a core requirement for smaller properties that may lack dedicated plant room space.

For commercial buildings with small to medium basin and sink led hot water demands and a desire to embrace a more sustainable business model, the FUSION hybrid hot water provides a single, easy to accommodate, highly effective response. One that provides optimum efficiencies, dramatically reduces carbon emissions and assures building regulations designed to lower carbon emissions from commercial projects are being met.

Learn more about ADVECO’s FUSION Hybrid Hot Water System

FUSION Commercial Hybrid Hot Water Systems from Adveco

  • FUSION is a complete range of low carbon hybrid heat pump and electric hot water systems
  • Resilient stainless steel water heating suitable for all UK regions
  • Compact design for new build and refurbishment projects seeking greater sustainability

Commercial hot water specialist Adveco, introduces the FUSION FPH-S range of low carbon, all-electric, packaged hybrid hot water systems. FUSION harnesses Adveco’s FPi32 Air Source Heat Pumps (ASHP), a high-pressure ATSH calorifier with electric immersion, controls, and metering to provide a reliable, high-temperature, sustainable and cost-effective system for new commercial build and refurbishment projects.

FUSION is available in 16 pre-specified variants with 6 or 10 kW preheat and 9 or 12 kW electric top-up, with capacities ranging from 200 to 500 litres all rated at 10 BAR for high-pressure applications. Able to meet a range of continuous capacity hot water demands from 257-377 litres/hour makes FUSION highly adaptable for a wide range of commercial buildings.

The FPi32 ASHP is specified to supply a working flow of 50°C for system preheat throughout the year, even when ambient air temperatures drop as low as -25°C. Electric immersion top-up then raises system temperatures in the calorifier to the necessary 60°C to meet commercial requirements for safe hot water demands. The stainless steel construction of the ATSH also makes it an excellent all-rounder, resistant to soft water corrosion and, with FUSION’s unique low electric immersion heat intensity (6W/cm²), is more resistant to scale build-up in hard water areas.

The physical design, dedicated controls and integrated metering ensure the ASHP preheat, and immersion work seamlessly to deliver the highest operational efficiencies. This enables FUSION to make the greatest gains possible from the heat pump, even when ambient temperature and system demands fluctuate. These gains offset much of the direct electrical energy usually required, delivering 53% carbon emissions saving and helping control the operational costs of providing business-critical hot water.

“For organisations with small to medium basin and sink led hot water demands and a desire to embrace a more sustainable business model, the FUSION FPH-S range provides a single, easy to accommodate, highly effective response,” says Bill Sinclair, technical director, Adveco. “By choosing one of these packaged hybrid water systems you gain optimum efficiencies, lower your carbon emissions and can be assured building regulations are being met for your commercial project.”

Fusion FPH-S Features

  • 16 pre-sized variants to meet a wide range of applications
  • 200, 300, 400 and 500-litre capacities
  • 6 or 10kW ASHP preheat
  • 9 or 12kW direct electric immersion heating
  • 257-377 litres/hour continuous capacity
  • 10 BAR high-quality AISI 316Ti and 316L stainless steel vessel (PED (97/23/EC), EN 12897)
  • Dedicated control system for simple operation and maintenance checks
  • Lower global warming potential with R32 ASHP
  • Compact space-saving form factor

Calorifiers and Hot Water Storage in Corrosive Water Conditions

For many companies, the assured availability of hot water is a business-critical issue, but one that can quickly become costly for those operating in the southwest and northwest of the UK, the Welsh coast and throughout Scotland. With a low pH, low total dissolved solids (TDS) and negligible buffering capacity, these naturally soft water areas prove highly corrosive to glass-lined vessels used as calorifiers and hot water storage.

Glass is, given the right conditions, generally resistant to attack from most chemicals and corrosive materials and easier to clean, making it a popular choice for lining steel vessels used in hot water systems. But corrosion is a complex phenomenon, and in naturally soft water conditions, despite the use of sacrificial anodes, glass-lined vessels can rapidly succumb to critical corrosive damage.

Pressure to Perform

In addition, the taller the structure, the greater the pressure requirements on the system, particularly since a common design choice is to locate the plant room in the basement. In order to meet, even small demands with a consistent, strong flow of hot water systems inevitably are oversized, adopting a larger, often bespoke tank.

This immediately exacerbates the existing threat, as oversizing, or the failure to correctly balance water flow also contributes to system corrosion. Oversizing of the pumps leads to high-velocity hot water circulating through the system and suspended solids in the water are driven against the metal leading to erosional corrosion. This process helps accelerate the soft water corrosion at points where water changes direction, such as when passing into or through tanks.

Glass-lined water vessels used as calorifiers and hot water storage under these conditions can potentially fail due to corrosion in a matter of just months – even with the use of sacrificial anodes. For these reasons, manufacturers will reduce or have even ceased to offer warranties on glass-lined products installed in these soft water regions. As a result, their specification into projects in these regions really can be a false economy.

Change to Resistant

Far more resistant to these water-side assaults are stainless steel vessels. Although there is a higher upfront cost, this would be easily offset by the relative longevity of the appliance. However, projects with smaller, yet higher pressure hot water demands, will still face the issue of oversizing. This further extends capital costs, of products, installation and the need for greater plant room space. As a result, project costs can become prohibitive for stainless steel, resulting in the specifying of the less expensive glass-lined alternatives gambling that they will prove resistant enough in the mid-long term.

Adveco addresses these concerns with its ATSx range of compact stainless steel, high-pressure hot water tanks. Specifically designed to serve as buffer vessels (ATSB) and indirect hot water calorifiers suitable for use with lower capacity, high-pressure commercial applications in soft water areas. The ATSx range provides specifiers and contractors with a wide choice of calorifiers and hot water storage vessels all rated to 10 bar as standard, which are by far the most efficient and cost-effective choice for businesses with smaller system demands.

Another advantage provided by the indirect water heaters in this range (ATSI, ATST, ATSH & ATSR) is that due to the transferral of heat through the walls of the heat exchanger element the two fluids do not mix. This allows for more options in terms of the external heat supply and introduces a range of renewable technologies that use other fluids for heat transfer including solar thermal collectors and Air Source Heat Pumps. The twin coil ATSR has been specifically designed for these lower-temperature renewable applications. These calorifiers are also relatively simple to install, since there is no burner, there is no need for a gas supply to be directly connected to the appliance and the is no requirement for a flue.

As with any hot water application, understanding the relationship between storage and recovery, and correct sizing is extremely important for efficient and cost-effective operation. Integrating a stainless steel calorifier within a hot water system gives you a number of design options, with a large efficient boiler a calorifier can be smaller avoiding unnecessary capital and ongoing operational expenditure. At 200 to 1000 litres the ATSx range provides a compact, tough resolution for lower demands applications in those soft water areas. If your project has pressure requirements greater than six bar, then the ATSx vessels are by far the most efficient and cost-effective choice for your project.

If the boiler is smaller, or demands for hot water are greater, then going too small means the storage could prove inadequate and the system will not achieve its operational requirements. For projects with larger demands or requiring greater customisation Adveco can support the project with the SSB, SSI and SST ranges of bespoke stainless steel calorifiers and hot water storage vessels.

Discover more about the Adveco ATSx range.

Learn more about soft water corrosivity.


Adveco commercial hot water and heating. Speak to Adveco about tackling global warming through efficient, low-carbon commercial hot water and heating systems (For schools, hospitals and care homes too!)

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COP26 – The Impact On Commercial Buildings

COP26 is now well underway with cautious optimism over initial agreements on reducing coal, global methane levels and rates of deforestation. But what does the event mean currently for those focussed on buildings in the commercial sector here in the UK?

Firstly, more than 40 nations representing over 70% of the world’s economy and every region have stated they will commit to ‘turbo-charging’ the uptake of clean technologies by imposing worldwide standards and policies at COP26. The five sectors that the plan will cover at first are steel, road transport, agriculture, hydrogen, and electricity, with the intent of encouraging global private investment in low-carbon technologies. The aim is to draw in trillions of dollars in private finance for cutting emissions, and businesses seeking to export into the EU must reach the same standards, so we can expect this to strongly impact the UK.

The Treasury has also outlined at COP26 new sustainability disclosure requirements (SDR) for large UK businesses. Under these new Treasury rules, financial institutions and companies with shares listed on the London Stock Exchange must come up with net-zero transition plans, which will be published from 2023. These net zero transition plans and sustainability claims must be ‘clearly’ justified to set a science-based ‘gold standard’. The government will set up a Transition Plan Taskforce of industry leaders, academics, regulators and civil society groups. The strategies will need to include targets to reduce greenhouse gas emissions, and steps that firms intend to take to get there. However, the government has admitted there is “not yet a commonly agreed standard for what a good quality transition plan looks like”, and the UK was not “making firm-level net zero commitments mandatory”.

450 firms managing banks, insurers and pension funds controlling 40% of global financial assets – equivalent to £95tn – have though aligned themselves to limit global warming to 1.5C above pre-industrial levels. Such private investment in green technologies over brown investments is vital in the march towards net zero by 2050. An example of this was the announced “Breakthrough Energy Catalyst” programme at COP26, which aims to raise up to $30bn of investments and bring down costs for ‘green’ hydrogen, direct air capture of CO² and long-duration energy storage.

But there still remain unanswered questions over what government support for the commercial sector is going to look like, and when it will materialise?  Non-mandatory regulation changes and dependence on private finance to green economic trajectory in the hope that businesses will decarbonise of their own accord remains questionable, especially outside the realms of big business.

At the start of 2021, there were 5.5 million small businesses that account for 99.9% of the business population (5.6 million businesses) in the UK according to the National Federation of Self Employed & Small Businesses. These companies’ buildings continue to generate a considerable proportion of UK emissions, so further support for them is critical. In the coming week, delegations will try to further raise awareness of the need for greater support if building emissions are to be successfully addressed.

Efforts to achieve large scale decarbonisation of buildings have focussed on new builds and recognising a building’s full lifecycle in terms of its carbon cost. But consider this, 97% of EU buildings are in need of renovation, so tackling existing properties must be addressed, only then can a more holistic carbon plan be put in place to support commercial properties to be more energy-efficient and able to support low carbon hot water and heating. This would not only address issues of embodied and emissive carbon but could help reduce air pollution and contaminants that, according to the World Health Organisation (WHO), contribute to the deaths of 120,000 Europeans a year. This issue is raised in an open letter to those attending COP26 from trade bodies that include the European Heat Pump Association amongst others, calling for action on appropriate air quality, thermal comfort, control and automation systems within buildings.

Read about how Adveco can help support your business to improve the sustainability of its’ buildings through our range of low carbon and renewable hot water applications.