All change for reduced emissions
The key to reducing carbon emissions from boiler plant is efficient boilers in well designed systems. STEVE HILLS explores the issues in the context of the revised Part L of the Building Regulations.With energy costs set to continue escalating over the coming months, and another revision to the Building Regulations pending, a change to the way designers approach boiler installations in new-build and, especially, refurbishment projects, is surely imminent. But to what extent will changes be necessary?
Energy Performance in Buildings Directive (EPBD) We are all aware of concern about the proposed new regulations due to come into force at the beginning of 2006. We have known for a long time that the UK Government is committed to the Kyoto Protocol, reducing emissions, saving energy and using renewable sources. With the impending new European Directive on the Energy Performance of Buildings 2006 and the consultative document on amendments to Building Regulations Part L (conservation of fuel and power) recently published for comment, I am sure everyone will be watching closely to see what develops.
Seasonal efficiency The EPBD has accelerated the next round of changes to Part L and the new regulations, which will require designers to comply with new seasonal-efficiency requirements for boilers. It is expected that there will be two performance thresholds — 80.8% gross for new buildings and 84% gross for existing buildings. The rationale behind these two thresholds centres on the higher energy performance characteristics of new buildings, compared with older buildings, and places a higher demand on energy performance to reduce emissions from existing buildings. This will have a major impact on the UK boiler-replacement market, which is around 70% of projects, as upgrading older systems to meet the new higher regulations has the potential to be a costly exercise, but do not despair.
Retaining best-practice principles If you are replacing existing boilers with high-efficiency condensing boilers, the good principles that designers use should not be abandoned. The proposed Building Regulations will probably mean that condensing boilers will be used more widely. The implication is that for refurbishment installations they will probably be installed in systems designed for higher temperatures; but by using common sense, an appropriate control system and a practical approach, potential pitfalls can be avoided. Over-complex systems and controls can lead to commissioning and maintenance problems, which result in poor operation and efficiency. An appropriate control system is essential for a boiler to perform at its optimum, and a well-designed system will eliminate a high number of stops and starts (short cycling) on boilers, preventing unnecessary wear and tear. Effective control of boilers is a significant factor in achieving good energy efficiency. Inadequate or incorrect application of boiler control can add 15 to 30% to fuel consumption. A system which is designed to heat a building when the outside temperature is –1°C will not be required to work as hard when the temperature outside is higher, so controls that can compensate the water temperature, based on outside temperature, will provide far superior efficiency and comfort for the building occupants. More significantly, compensated temperatures maximise the opportunity for condensing performance. One of the most important elements for effective control of multiple boiler systems is good design of the hydraulic system. A separate constant-flow primary circuit is generally recommended for modern boiler systems, to ensure effective and safe operation. This is best achieved using a single primary pump set to provide the constant flow rate. Constant flow also helps the stability of sequence control, as the temperature is then more representative of the load on the system. Hamworthy uses pumps for heating and hot-water applications with performance characteristics which enable very close matching of the pump with the requirements of the system. Low-speed pumps, which can reduce system noise, and energy efficient pumps contribute to the energy performance of the system. Reduced standing losses and improved part-load efficiency of modern low-water-content boilers allow very simple hydraulic arrangements to be used for multiple boilers. These simple layouts do not require individual boiler pumps or automatic isolation valves, which are the cause of many problems associated with controlling multiple boilers.
Modulating burners in multiple boiler systems Accurate load matching is a key advantage of multiple boilers. In the past, using a number modules with on/off operation, was the route to modulation in commercial boilers. When boilers operate under part load, the water return temperature begins to rise, and a sequence controller switches boilers off in turn for short intervals, to bring the average mixed-flow temperature back to the set point. Modern high-efficiency boilers use modulating burners. With fully modulating sequence control, each module can reduce its output down to 20%, following the heat demand with greater accuracy. The advantages of multiple -boiler arrangements and the accurate load matching of modulating boilers are combined. Fully modulating condensing boilers allow the heat output to be adjusted exactly to meet demand. Unlike traditional boilers, which were switched off as demand reduced to maintain maximum performance on each boiler, modulating boilers are their most efficient at part load. This means that rather than switch boilers off, boilers should be modulated in unison to maximise efficiency performance.
High-efficiency boilers and flue systems There are two important factors to consider when flueing high efficiency and condensing, boilers. First, flue-gas temperatures are lower, which creates less buoyancy and so requires fan assistance (in the boiler) to exhaust the gases, resulting in a positive pressure in the flue system. Secondly, the flues gases will be wet, so a watertight flue system is essential to prevent unsightly leaks and associated problems. The preferred solution is a modular, twin-walled, insulated flue solution specifically optimised for condensing and high-efficiency boiler applications.
Project support Hamworthy Heating works diligently to provide solutions that will exceed forthcoming regulations, investing heavily in research and development to ensure its customers get the highest quality products. Working closely with engineers and specifiers at the design stage enables us to provide project support where and when it is needed. The company can also provide design specifications for flue systems and other ancillary products associated with plant for heating and hot-water systems.
Steve Hills is commercial director with Hamworthy Heating Ltd, Fleets Corner, Poole, Dorset BH17 0HH.
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