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Taking efficiency to the max

Retrofit and boiler replacement have a vital role to play in meeting our environmental targets, says Andy Green technical director at Baxi Heating. The focus now must be on optimising system performance for maximum efficiency savings

Andy Green technical director at Baxi Heating

As we learn to live with COVID-19, addressing the energy efficiency of our commercial buildings is more important than ever. While energy consumption in unoccupied buildings may have fallen during lockdown, now is the opportune moment to prioritise energy efficiency improvements before energy demand and prices rise once more.

Energy efficiency is also a fundamental pillar in the UK’s path to net zero. And with over a third of UK emissions coming from heat in buildings, this is an obvious target for improvement.

As we work towards full decarbonisation of heat, a range of approaches and solutions will need to be employed to meet the unique requirements of individual buildings. This is likely to include low

carbon technologies such as heat pumps in well insulated commercial properties and heat networks in dense urban environments. The feasibility of repurposing the existing gas grid to transport green gas is also being explored by ourselves and others to offer a low disruption option towards decarbonising our older building stock.

But we mustn’t neglect the cost-effective opportunities that are available now to reduce energy demand and emissions from heat in buildings.

Replacing any ageing or inefficient boilers with high efficiency condensing boilers and adding the appropriate controls, for example, has the potential to deliver significant efficiency savings for rapid financial payback. The focus now must be on optimising performance for maximum savings.

With that in mind, let’s consider some of the challenges when refurbishing older heating systems and how best to overcome these hurdles for maximum efficiency gains.

Accurate sizing

Given that extensions to a building or improvements to its fabric since the previous boiler plant was installed are likely to alter demand, it’s clearly essential to understand the building’s actual requirement. And as a building’s use or occupancy rate may have changed considerably post COVID-19, a reassessment is particularly relevant at the present time.

Cascades

Efficiency is the key requirement in any commercial heating upgrade. However, as the new system will generally need to fit into the space designed around the old boiler, accessibility and available space will also need to be considered when determining plant configuration.

Wall hung boilers are typically the boiler of choice due to their compact size and their ability to be installed in cascade arrangement.

Cascade systems comprise multiple linked boilers which can respond more efficiently to changing heat loads and are easier to size to specific building needs.

Selecting boilers with a high modulating ratio will ensure that each boiler can adjust its operating capacity in line with demand for more efficient operation.

A cascade configuration also offers a high turndown capability and improves the modulation capability of the boilers for more efficient operation.

The inbuilt redundancy provides greater reliability while the design also makes for easier maintenance – leading to higher lifetime efficiency – as the boilers are easier to isolate, remove and replace, reducing labour and downtime.

Maintenance areas

But in low-ceilinged cramped basement plant rooms, wall hung boilers may not always be an option.

Fortunately, smaller, more lightweight floor standing condensing boiler models are now available that are easier to manoeuvre safely into position. Additional features like the inclusion of integral wheels or the ability to disassemble high output boiler into parts again smooths access constraints and associated costs.

However, it is not just the boiler footprint that needs to be calculated as maintenance areas, access space and walkways must also be factored into the available space.

Clever use of modern boiler service area can overcome this hurdle. For example, with the latest floor standing boiler models, like Remeha’s Gas 120 and 220 Ace, ultra-compact modular configurations can be achieved that usually only require access at the front for space-saving design. And while interconnecting pipework tends to be placed above the units, at a similar height to a vertical-stacking arrangement for example, the modules are all at the same height. This enables maintenance to be carried out easily and safely at a lower level to keep efficiencies high throughout the life of the boiler.

Water quality

Heating and hot water systems perform more efficiently, more safely and more reliably with good quality water circulating in them, making this a critical factor for consideration at the planning stage.

Hydraulically separating the primary and secondary circuits using a plate heat exchanger will prevent any debris or contaminated water entering the new boilers, increasing their longevity and durability while optimising their operational performance and the overall efficiency of the system. Introducing air/dirt separators will also help protect the new boilers and optimise their performance.

Controls

It’s important to note that condensing boilers require a different approach to controls than non-condensing boilers. When installing new boilers onto an old system, for example, it’s advisable to introduce a controls strategy that will include weather compensation to enable the boilers to run at lower temperatures, where they can operate in condensing mode and achieve their higher efficiencies.

The addition of thermostatic radiator valves (TRVs) or temperature zone control will again increase overall seasonal efficiency through full building control.

Disruption

Avoiding disruption to the heating and hot water system during the changeover period can be vital in buildings like schools and hospitals.

One option that overcomes this challenge and addresses all of the previous refurbishment obstacles, is to use offsite fabricated heating solutions for multiple wall hung or floor standing boiler replacement projects.

With turnkey solutions like prefabricated rig systems, all project and site requirements – from space and access limitations to water quality, project specific controls and optimal pipework for connection to the system – can be addressed in advance at the design stage.

Typically, each boiler rig system will be designed using BIM tools and 3D computer-aided design (CAD) systems. Front-loading the design in this way provides specifiers and contractors with the opportunity to provide input at the early stages, while bringing assurance of a quality outcome.

With installation and commissioning reduced from weeks to just days, turnkey solutions like these minimise disruption through faster project completion. At the same time, they reduce safety issues through controlled off-site fabrication and maximise energy savings benefits through best quality installation.

Time to act

Ensuring that the heating system operates effectively and efficiently is a practical means of avoiding needless energy waste and associated emissions. 

A reliable, well-controlled heating system will not only minimise building running costs in these difficult times but is central to generating a comfortable and productive environment for returning workers. And where more fresh air needs to be brought into a building’s HVAC system, or windows opened to improve ventilation and prevent transmission of the virus, an efficient heating system will be better able to optimise thermal comfort.

With good manufacturers providing quality solutions backed with expert technical advice and support for best practice heating refurbishment, there’s never been a better to time to prioritise heating efficiency.

Wall hung boilers are typically the boiler of choice due to their compact size and their ability to be installed in cascade arrangement.

Cascade systems comprise multiple linked boilers which can respond more efficiently to changing heat loads and are easier to size to specific building needs.

Selecting boilers with a high modulating ratio will ensure that each boiler can adjust its operating capacity in line with demand for more efficient operation.

A cascade configuration also offers a high turndown capability and improves the modulation capability of the boilers for more efficient operation.

The inbuilt redundancy provides greater reliability while the design also makes for easier maintenance – leading to higher lifetime efficiency – as the boilers are easier to isolate, remove and replace, reducing labour and downtime.

Maintenance areas

But in low-ceilinged cramped basement plant rooms, wall hung boilers may not always be an option. Fortunately, smaller, more lightweight floor standing condensing boiler models are now available that are easier to manoeuvre safely into position. Additional features like the inclusion of integral wheels or the ability to disassemble high output boiler into parts again smooths access constraints and associated costs.

However, it is not just the boiler footprint that needs to be calculated as maintenance areas, access space and walkways must also be factored into the available space.

Clever use of modern boiler service area can overcome this hurdle. For example, with the latest floor standing boiler models, like Remeha’s Gas 120 and 220 Ace, ultra-compact modular configurations can be achieved that usually only require access at the front for space-saving design. And while interconnecting pipework tends to be placed above

16 September 2020

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