Out With the Old

Two in every three commercial boiler installations are replacements, so contractors often face the challenge of integrating the old with the new. Chris Caton, Head of Commercial Product Management at Ideal Boilers, outlines the key issues to consider when planning a replacement installation.

Quality boilers can run for a long time, but – inevitably – every boiler has its day. In fact, a surprising number of organisations unknowingly incur excessive heating bills because they continue to run a system that has been made outdated by more efficient, modern versions. Ageing boilers can cost more in repair and running costs than a replacement, burning money without giving out any noticeable heat.

Whether a boiler is no longer serviceable, or it’s approaching that time of year when refurbishments are taking place, there are several things building services engineers need to consider to protect every level of the chain. For example, many schools will be considering upgrades at this time of year and, because they may require heating across buildings that span a variety of ages, layouts and uses, versatile solutions may be needed.

It sounds simple, but people rarely consider the building use. During the consultation stages, it is worth urging the client to think about using or creating a different space for any new boilers, which would minimise downtime from the old system being shut down. It’s also important to remember that multi-use buildings can be heated by one system, but may need a control system intelligent enough to manage different areas at the same time.

Another consideration for public sector buildings – particularly schools and healthcare establishments – is the appetite to install a heating system that can be backed up. No-one enjoys being without heat and hot water for long, but downtime in many commercial applications – whether for routine maintenance or because of mechanical breakdown – can be disruptive, expensive, and even damaging to reputation or health. So a cascade set-up could be the solution. For example, rather than two 300kW units making a total output of 600kW, six 100kW boilers arranged in cascade will give the same output and – in this scenario – an even greater modulation rate of 30:1.

The main risk with an old building is the sludge and dirt that accumulates in its system over the years, which risks being deposited in the new boiler. Blocked waterways resulting from this debris can cause a premature failure of the boiler.

Costs on some projects can escalate, and levels of protection – such as plate heat exchangers and magnetic filters – can sometimes be taken out of a proposal. When looking at the life-cycle costs of boilers, however, this is a potentially risky move. System protection is the key to extending the lifespan of a boiler and, by communicating the long-term savings to an end user, you add value to your services.

Open vented v sealed

It is crucial to think of the whole system when installing new condensing boilers. Older heating systems will probably be open-vented, with a feed and expansion tank, which means pollutants can enter the system water.

Installing new boilers onto an old system that is clogged with debris and dirt will immediately reduce their effectiveness. If dirty water is transferred into new boilers, it will affect their ability to run efficiently and, potentially, lead to breakdowns and even failure.

Before installation, we encourage installers to consider treating the water within the existing system. This helps to ensure the boiler’s longevity and can protect its internal parts from corrosion and the build-up of scale over time.

If introducing a new boiler installation to an existing system, another consideration is ‘system separation’ via a plate heat exchanger. This transfers heat from the primary circuit to the secondary without the system’s potentially dirty water coming into direct contact with the circuit. It also maintains a constant water velocity, despite changes in the secondary circuits. This eliminates the need for a low-loss header, as the system’s pumps won’t have influence over the boiler shunt pumps. A heat exchanger will only function at its peak efficiency, however, when the water velocity passing through it is maintained within prescribed parameters. So accurate sizing of the plate heat exchanger is required before installation.

By taking a life-cycle costing approach to installing new boilers in an old building, a business can realise multiple financial benefits over the lifetime of the boilers – and while it’s easy to win business on price, reputation lasts much longer. Key things to remember when approaching a boiler retrofit are: system preparation and ongoing water treatment; adding levels of protection, such as low loss headers, plate heat exchangers and filters; and understanding the needs of the occupants. If these are considered and clearly communicated to the customer, it’s a win-win for all involved.

This article first appeared in CIBSE Journal Commercial Heating Supplement, May 2018.