Boilers & Burners
Mark Wilkins is technologies and training director at Vaillant
Contrary to myths, a system where the boilers are cascaded does not waste energy
Why oversizing is essential
Mark Wilkins explains why redundancy is essential for many commercial applications, how it is implemented and why oversizing is unavoidable in these cases
O
versizing a heating system accidentally should never happen. However, implementing a redundancy contingency in certain plant rooms is not only wise, but the deliberate over-sizing by adding additional back-up boilers in cascade can offer a range of benefits. By controlling and designing such systems in the right way, heating systems can be used efficiently, alternating the heat between boilers so that they are effectively being used less, therefore improving the lifespan of the product while providing essential and comfort conditions. There is a wide range of nondomestic buildings where the provision of heat is critical to an organisation’s operations. To ensure heat security, redundancy is built into the heating system using ‘spare’ boilers. Without this back up to deliver heating and hot water, lives could be put at risk, businesses could incur significant losses, and occupants could suffer disruption to important aspects of their daily lives. Protected services such as hospitals and nursing homes need hot water and heating to keep vulnerable
patients safe, comfortable, and ensure maximum hygiene on the premises. Thermal comfort is also essential in educational establishments and childcare settings, as set out in the requirements of Building Bulletin (BB) 101. Adherence to the guidelines not only contributes to occupants’ physical health, but also the ability of both staff and pupils to concentrate. Loss of heating and hot water could lead to building closures and disruptions to their education. The Health and Safety Executive also places constraints on employers to provide basic comfort and care to their employees, so there is a legal framework in all workspaces, even in office environments. Heat is not only needed to keep people safe and comfortable. Many industries require heat and hot water for manufacturing processes. Without these, production would grind to a halt, resulting in significant losses to businesses. In museums, humidity levels and temperatures must be kept constant to preserve valuable artefacts. If their condition is not maintained, this could result in damage to irreplaceable objects which have historical and cultural significance to a country.
Installing a system with cascaded boilers is advantageous in that it operates at its maximum capacity during the highest heat demand. At the same time, it can guarantee heat security if a failure occurs or during essential maintenance.
Meeting heating demand
For example, in a nursing home with a 600kW heating demand, six or seven Vaillant ecoTEC plus 120kW boilers could be set up as a cascade. This ensures that the heating demand can be met with five units fired up, with one or two spare units as back-up. Should a fault occur, for instance if one boiler doesn’t fire up as needed, the Vaillant VRC 700 controller, which can be used in a cascade set up with
The units in a cascade are not idle, they are operational under normal circumstances
up to seven boilers, would recognise this and simply use one of the others to continue delivering heating and hot water. The backup units in a cascade system do not sit idle, they are fully operational under normal circumstances. This is because the operator can programme the controls so that all units, including the spare ones, work on a rotational basis and manage changeovers. There are two important advantages to this set-up. By spreading the load, the risk of breakdowns in all units can be reduced, and their life can be prolonged. Using the back-up equipment regularly also ensures that they would operate when needed. There are other circumstances where the inclusion of back-up boilers could result in even greater oversizing. For example, in a commercial building with a heat demand of say, 280kW, while a 280kW ecoCRAFT may be able to support the heat demand, for increased system flexibility and heat security, it’s often more effective to install three 120kW boilers, oversizing by a total of 80kW. In this case, the system would be oversized by 30 per cent. But if usage is rotated equally between the three units, at any given time two of the boilers would be covering more than 90 per cent of the heat demand, so a product such as a Vaillant commercial boiler could operate well beyond the 15-year industry-expected lifespan. Contrary to myths, a system where the boilers are cascaded does not waste energy. They are controlled so that only some of them are fired up to provide the amount of heat required at any particular time. Vaillant’s VRC 700 can automatically manage this process for cascade installations with up to seven Vaillant boilers, and integrate with any BMS via additional accessories. If there are more than seven Vaillant units, they can integrate directly with the BMS via additional accessories, so that building operators can manage their heating in the most energy-efficient way. Plant sizing shouldn’t be exceeded, and system diversity factors should be used correctly. However, plant rooms must be capable of all the challenges it is designed for. Having redundancy in a heating system not only prepares a building in the event of breakdowns but can also extend the lifetime of the system when designed and controlled wisely.
22 | ENERGY IN BUILDINGS & INDUSTRY | APRIL 2022
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