Bill Sinclair, Technical Director, Adveco, considers the latest developments in commercial condensing boiler technology and how this can help meet the needs for sustainability and lower the cost of ownership
Faced with balancing the business-critical need for space heating against stricter legislation and the demand for greater clarity of what they are doing to reduce emissions, how can UK commercial organisations better address the heating demands of their large buildings?
With the majority of national infrastructure currently ‘on gas’ and delivering half of UK’s non-transport primary energy needs, gas-fired boilers remain the best option for the provision of heating. The increasingly stringent government legislation that industrial and commercial establishments face in terms of reduction of carbon emissions and hazardous air pollutants is driving the specification of systems that are based on high efficiency condensing boilers, or a hybrid approach that combines these boilers with heat pumps to provide low carbon, effective heating. In such a scenario, the continuous low-grade heat from the heat pump works alongside the fast responsiveness of the gas boiler which is used to top up heating and avoid the requirement for higher carbon-emitting generators at electricity peak demand times.
Requiring less fuel, due to recovery of latent heat from vaporisation, high efficiency condensing boilers can lower running costs and provide higher temperatures than a heat pump. Offering reliable operation, simple controls and compact design we are seeing increasing interest in adopting hybrid technology as a practical response to the consistent need for commercial heating and the wider requirement to be compliant with latest legislation.
Reducing the cost of business-critical heating
As an independent provider of heating systems, identifying technology concepts that will address sustainability is only the start. We also recognise the need to meet customer requirements for cost of ownership, which can be met through several features, from space savings, ongoing supply reliability to simplified control and maintenance that provide peace of mind when investing in a business-critical heating system. From restaurants and hotels, to leisure facilities, schools and university accommodation the needs are increasingly universal for large application, very efficient and low emission heating.
Whether limited by existing structures in a refurbishment, or reducing cost in a new build, saving space is an important consideration. But when a system demands more than 300 kW output there has been little option other than to build a costly frame and implement a design incorporating the necessary wall-hung boilers in cascade until the system’s needs are met. By which point you effectively have a floor standing system that negates the space advantages of a wall-hung boiler. For this reason, some will consider a floor standing alternative, they are after all relatively low cost and can supply high loads. The problem is that such appliances offer a single fan, gas valve and heat exchanger which means there is no system redundancy. That makes for false economy when it comes to delivering a space-saving, consistent 24/7/365 heating system.
We would advocate a modular cascade concept that takes full advantage of the compact size afforded by condensing natural gas or LPG boiler technology, with low water content heat engines, built-in redundancy and no need for an expensive framework to convert wall-hung boilers to floor standing.
Adveco’s MD, for instance, can be used to create a cascade of up to eight 280 kW units, each combining four 70kW heat engines pre-stacked in a single, elegant casing. This approach can provide more than 2200kW while occupying minimal plant room floor space and assuring clearance for maintenance. The need for, and cost of a frame is immediately negated, and issues of limited headroom are quickly resolved. A high maximum run pressure, up to 11 bar, makes it highly suitable for large, high-pressure applications.
We can also demonstrate a turn down as low as 14 kW and 94% redundancy in case of failure. Of course, while built-in redundancy is advantageous, the supply reliability should not hinge on redundancy systems but features that are designed to prolong the life of the appliance.
Typically, new condensing boilers will be fitted with a heat exchanger made from non-ferrous metal, usually stainless steel, to counter corrosion. Adveco’s MD incorporates unique and extremely high-quality AISI 316Ti heat exchangers constructed from a continuous, non-welded run of titanium-stabilised stainless steel. This approach reduces weak points and offers improved strength and corrosion resistance at high temperatures for long periods of time, reducing the chance of failure while ensuring high capacity heat transfer.
The patented design features a large bore, three-pass arrangement with circular, not flattened, cross-section tubes to reduce the collection of debris. To maximise condensation means operating at a sufficiently low temperature, and this requires condensing boilers to be tolerant of the condensate. The inclusion of a refillable limestone bed is truly advantageous, neutralising acid condensate which can dramatically affect the lifespan of an appliance.
Each heat exchanger also incorporates a control board that allows communication and load balancing across adjacent exchangers, meaning that the system not only provides built-in redundancy, but also offers improved reliability and longevity as all internal components receive uniform wear. This integrated system control not only provides an intelligent maintenance self-check of all primary appliance components and functions, but also incorporates MODBUS communication and alarm output to assist with BMS integration.
As a result, condensing boilers can meet the demand for reliability and efficiency for lower cost of ownership. We go as far as to offer an industry-leading 10-year warranty on the MD’s heat exchangers and burners, with a seven-year parts and labour warranty for long-term peace of mind.
Meeting Commercial Sustainability Goals
We can easily demonstrate the functionality and the cost savings of adopting a modular cascade concept with high efficiency condensing gas boilers, but what of the air quality and sustainability of the technology?
To improve combustion efficiency, condensing boilers operate so that the water vapor in the exhaust – which contains about 464 kJ/kg of latent energy – condenses on the heat exchanger and not in the flue or outside the building. Designed so that the highest efficiency is at the low end of the firing range, condensing boilers typically operate at 94-95% combustion efficiency. In the case of the MD, a high-efficiency pre-mix burner achieves ideal combustion efficiency of up to 107% (net)/98% (gross) reducing energy costs and producing low emissions. With low CO and NOX emissions, a heating system built around a high efficiency condensing boiler (Class 6 appliance) satisfies the requirements of the Energy-related Products (ErP) directive.
Correctly sized and professionally commissioned, a cascade system with high-efficiency pre-mix burner provides a high 1:20 modulation ratio. This large modulation range, along with built-in cascade control ensures that efficiencies are maximised no matter the heating load of the building. With the input of the boiler easily altered to closely match the heating load, the system is better able to derive as much heat out of the exhaust gases as possible. This efficient reuse of heat results in low flue gas temperatures allowing for the use of standard 80-160mm diameter plastic flue pipe (PP). PP is efficient, environmentally friendly and significantly cheaper than stainless steel, offering 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 – from hybrid systems to the introduction of green gas with its lower carbon footprint. For commercial projects that face the most stringent legislation and oversight, high-efficiency condensing boilers remain a realistic and effective means of meeting the demands for improved sustainability, while offering considerable economic advantages in terms of operational costs for built assets.