Water heating

Evolving to a sustainable future

Adevco AD 280T cutaway showing quad heat engine arrangement


ncreasingly stringent legislation to reduce carbon emissions and hazardous air pollutants has driven the specification of systems that are based on both high-efficiency water heaters, or a hybrid approach that combines water heaters with heat pumps to provide low carbon, effective hot water.

Reducing costs

Glass-lined steel water heaters, given the right conditions, remain an attractive proposition as the glass is generally resistant to attack from most chemicals and corrosive materials. The development of this glass, a blend of oxides and silicates has been continuously developed since Adveco introduced the technology to the UK in the early 1970s. Temperature, duration, and the concentration of reagents will affect the rate of corrosion, so for example, the presence of fluorides at any temperature will corrode a glass-lining. This is exacerbated in purer, naturally soft water areas, where low electrical conductivity reduces the protection offered by sacrificial and powered anodes. This can lead to glass-lined vessels rapidly succumbing to critical corrosive damage, with larger vessels typically more prone to the corrosive nature of soft water. For this reason, commercial hot water systems where water is particularly soft should be using a stainless-steel appliance. Though more costly than glass-lined appliances, they are less susceptible to water-side corrosion and combustion-side assaults. Typically, condensing water heaters will be fitted with a heat exchanger made from a non-ferrous metal, usually stainless steel, but we would recommend heat exchangers constructed from a continuous, non-welded run of titanium-stabilised stainless steel. This new alloy reduces weak points and offers improved strength and corrosion resistance at high temperatures for long

periods of time. This not only reduces chances of failure, but ensures high-capacity heat transfer. The Adveco AD makes use of this alloy in an efficient three-pass design that creates large bore, circular cross sections to additionally reduce scale formation. Heat exchangers also need to be able to communicate, enabling load balancing across adjacent exchangers, providing built-in redundancy as well as improved reliability and longevity from more uniform wear. We would advocate a modular cascade concept that takes full advantage of the compact size afforded by the latest generation of condensing natural gas or LPG water heater technology. Floor-standing water heaters, such as Adveco’s AD, can be connected at a minimum of 10cms, linking up to eight 280kW units each combining four 70kW heat engines pre-stacked in a single casing in cascade. This not only occupies less plant room floor space and alleviates issues of limited headroom, but also negates the need for a costly fame. Such a system offering 2,352kW can supply up to 1,070 litres per minute, more than enough for larger scale applications.

Emissions & sustainability

Designed so that the highest efficiency is at the low end of the firing range, condensing water heaters typically operate at 94-95% combustion efficiency. The inclusion of a high efficiency pre-mix burner can achieve ideal combustion efficiency of up to 106% (net) reducing energy costs and producing low emissions. With low CO (19ppm) and NOX (27mg/ kWh) emissions, a hot water system built around a high efficiency condensing water heater easily satisfies the requirements of the current Energy- related Products (ErP) directive.

Correctly sized and professionally commissioned, a cascade system with high efficiency pre-mix

Adveco AD premix burner cutaway

With the requirement for high temperature (60°C) and the majority of national infrastructure currently ‘on gas’, gas-fired water heaters remain a realistic option for the provision of commercial hot water according Bill Sinclair, technical director at Adveco

burner can provide a high 1:20 modulation ratio. This, along with built-in cascade control ensures that efficiencies are maximised no matter the hot water demands. With the input of the water heater easily altered to closely match the demand, the system is better able to derive as much heat out of the exhaust gases as possible. Efficient reuse of heat results in low flue gas temperatures, allowing standard 80- 160mm diameter plastic flue pipe (PP) to be used. Environmentally friendly, and significantly cheaper than stainless steel, PP offers a cost-effective and space saving alternative in terms of pipe run. Whilst arguments continue to rage regarding the validity of gas for a low carbon future, the reality is that for the foreseeable future our national infrastructure will continue to remain heavily reliant on the provision and improved use of gas. For commercial projects that face the most stringent legislation and oversight, high efficiency condensing water heaters remain a realistic and effective means of meeting the demands for improved sustainability. Right now, this takes the form of a hybrid systems approach where continuous low-grade heat from a heat pump works alongside the fast responsiveness of the gas water heater to top up at electricity peak demand times avoiding the requirement for higher carbon emitting generators.

Looking forward, we envisage the wider adoption of hydrogen powered commercial water heaters as the gas infrastructure transitions to a blended supply, first at a regional level at the end of this decade, then to national scale supply in the 2030s and 2040s. Crucially, gas continues to offer considerable economic advantages in terms of operational costs for built assets and a familiar, proven energy technology for bridging incumbent systems with future generation technologies that will aid delivery of Net-Zero.

16 April 2021

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