When it comes to making efficiency improvements, replacing an existing boiler like-for-like is usually the preferred solution. However, fitting multiple boilers on a cascade system can offer bigger efficiency savings than one large output boiler, as well as save money long-term and provide an increased level of redundancy. Steven Evans, national sales director at Potterton Commercial, explains the benefits cascade systems can bring to building managers.
With new EPC regulations coming into force a couple of months ago, energy use should be front of mind for all facilities managers. All properties rented in England and Wales need to achieve an EPC rating of at least an E before they can be let to new or existing tenants. As heating and hot water account for 60% of total energy use in a commercial building, reviewing your existing heating system and upgrading or replacing equipment as necessary is one of the most effective ways to boost an inadequate score.
Many buildings still rely on non-condensing boilers which are only 70 to 80 per cent efficient compared to modern, condensing boilers which can achieve more than 90 per cent 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.
But 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.
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.
Here are the main reasons why you should consider fitting a cascade system:
- Efficiency wins
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 two boilers on a cascade set-up have a maximum output of 510kW, 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.
- Back-up plan
More than one boiler in a system adds a layer of redundancy as in the unlikely event that one breaks down, the system will continue to operate, albeit at reduced levels. This is particularly beneficial in healthcare settings, where continued operation is vital to maintain the safety and comfort of the occupants. Often, these types of premises will employ multiple boilers for heating and separate, direct, gas-fired water heaters for hot water delivery.
- Flex your outputs
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 has been a tendency to oversize boilers, which often comes about due to a natural desire to err on the side of caution to avoid complaints from users about under-performing systems. Thankfully, the flexible and modular nature of a cascade system helps to negate this issue.
- Space saving solution
They 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.
- Servicing made easy
When it comes to service and maintenance, a cascade system allows engineers to work on each individual boiler, whilst the remaining boilers on the cascade stay switched on – reducing disruption to building occupants.
When replacing an older boiler, it should never be assumed that like-for-like replacement in terms of boiler capacity offers the best solution. Boilers have often been specified without considering the building’s heat gains from people, lighting and equipment. Even if such heat gains were taken into account when the original system was sized, changes in use, occupancy, and amount and type of heat-emitting equipment may have occurred over time. Therefore, it is 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.
A cascade design can deliver both efficient performance and significant cost savings. For facilities managers that are looking to upgrade or replace their systems, cascades should be considered in parallel with modern high-efficiency condensing boilers.