Oct 23, 2019 Last Updated 10:52 AM, Aug 14, 2019

Why you should consider a water cascade

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With energy efficiency high on the agenda for facilities managers of public sector buildings, it’s crucial that heating systems are not only cost-effective but deliver maximum carbon savings too. Steven Evans, National Sales Director at Potterton Commercial, explains how alternative approaches to boiler system design, such as cascades, can deliver important savings.


This summer, the Government reiterated its commitment to reducing greenhouse gas emissions across the UK public sector estate, by publishing ambitious new targets. Business Secretary Greg Clark announced plans to reduce emissions by 43% by 2019/20 against 2009/10 levels – an initiative that is estimated to save the public purse around £340m.

Clark hailed the cost savings already achieved through the public sector emissions reduction drive. Last year, the public sector saved £104m after meeting a previous goal to reduce public sector emissions by a third by 2020 three years earlier than planned.

The greenhouse gas target includes emissions from energy, waste, water use, lighting and estate management. The Government said it would also be pushing other public sector bodies to publish guidance on how to drive down bills and cut carbon in their operations.

With the public sector under increasing pressure to set and tackle new energy efficiency targets, one of the first areas that comes under scrutiny is heating. And justifiably so, when we consider that many buildings still rely on non-condensing boilers. These are only 70 to 80% efficient compared to modern, condensing boilers which can achieve more than 90% thermal efficiency.

So, it’s a no-brainer that replacing a non-condensing boiler and updating controls will also save you money on your annual heating bills. In fact, you can save up to 25% of energy costs, depending on consumption.

However, product replacement is just one part of the solution. Alternative approaches to boiler system design, such as cascades, should also be considered to provide even greater efficiency and long-term cost savings.

Cascade design

A cascade system is two or more boilers electronically controlled on a common hydraulic header. The ‘master’ boiler is the primary appliance, sending commands to each of its subsidiary boilers according to the demand for heating and/or hot water.

Boiler cascades offer greater efficiency as they have a high turndown rate, with a substantial difference between the highest and lowest output available. For example, six 90kW Sirius Three boilers on a cascade setup have a maximum output of 540kW, but an individual boiler can also modulate down to 10kW to save energy when demand is not present.

Multiple linked boilers can respond more effectively to varying heat loads, making a cascade the perfect solution for buildings with changeable demand schedules. This is particularly relevant for buildings in the public sector, which might be operational at different times of the day and through the night.

The advantage of having more than one boiler in a system is also that it adds a layer of redundancy whereby the system will continue to operate in the unlikely event that one breaks down. Critical facilities in the public sector such as healthcare depend on having a backup that ensures continued operation to maintain the safety and comfort of a building’s occupants.

Flexibility and scalability

Cascade systems also offer greater choice and flexibility of outputs. This allows the size of the plant to be more closely matched to the exact heat requirements of a building. It has long been recognised that there is often a tendency to oversize boilers and to err on the side of caution to avoid complaints from users about under-performing systems.

The flexible and modular nature of a cascade system helps to negate this issue, with options to add capacity to the heating system according to the changing needs of the building. In the public sector, this flexibility provides planners and managers with more options for assigning different uses to different buildings on their estate.

Cascade solutions also offer a suitable alternative when space is at a premium, as the system can be broken down into smaller components and easily transported through tight spaces. Cascade frames come in many shapes and sizes, including corners, to meet the requirements of all types of plant room.

When replacing an older boiler, it should never be assumed that like-for-like replacement in terms of boiler capacity offers the best solution. It is always important to size a replacement installation based on the current building requirements, rather than rely on the size of the boiler originally specified.

An additional consideration when installing a cascade system is flue design. Each boiler requires an individual, condensing flue to ensure products of combustion are safely removed from the premises. With the potential for up to 12 boilers in a cascade system, this can be tricky. A common workaround is for each flue to feed into a flue header, through which waste gases are expelled as per requirements.

The political pressure on public sector organisations to hit new targets for energy efficiency is only expected to intensify over the coming years. What’s more, changes to the regulatory environment is placing heating systems under more scrutiny than ever before.

Building managers need to make sure they not only meet current requirements but put in place solutions that meet future needs. For those looking to upgrade or replace their systems, a cascade solution can provide the answer by delivering both efficient performance and significant cost savings – a modern heating system fit for purpose for years to come.

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