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For further information,
please contact:
Linden Shuttleworth
07711004815
linden.shuttleworth@flaktwoods.com
As prepared for ACR Today
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The fan coil is dead, long live the chilled beam?
Well, not quite. As long as fan coil sales remain ahead of chilled beams, reports of their demise are premature, although there is little doubt about the way that the HVAC world is moving. Market figures released late last year (European Market for Chilled Beams/Ceilings UK, BSRIA, December 2007) showed the gap between the two cooling technologies disappearing fast by the end of 2006: €22.9m for chilled beams, against €40.6m for fan coils (£16.4m vs. £29m, at €1.4 : £1).
With last year’s known orders suggesting not just that chilled beam sales continue to grow rapidly but that this rate of growth is increasing, most observers predict that they will be seen to have overhauled fan coils during 2007. BSRIA predicts €56.7m (£40.5) in sales of chilled beams for 2010, against just €49m (£35m) for fan coil units: growth of 127% against growth of just 21%. There is no doubting that the look and feel of the terminal unit market has changed significantly within less than a decade.
A market shift of this magnitude typically happens when innovation brings better technology to market, but chilled beams have been around for some time. While they first started to make an impact in the UK during the mid-1990s, Scandinavian users have been enjoying their benefits for more than 20 years. There certainly has been significant evolution in chilled beam technology, but that is not the only factor engendering their increased popularity. Almost as important has been a changing environment within which beams and coils are specified and installed. In order to understand the drivers behind the continuing shift in market preferences, it is useful to review the fundamental concepts.
Whichever means is used, the underlying principle is that an area has to be cooled by lowering its air temperature. From that starting point, there is a choice of technologies.
At its most basic, a fan coil unit typically comprises a fan driven by an electric motor, a heat exchange coil, some means of collecting condensate and an air filter. The temperature of the ambient air is lowered through blowing it by the fan across the coil, which contains chilled water, and onwards into the area to be cooled. Such a unit offers flexibility of location, being able to be sited either inside its own standalone cabinet in the area to be cooled or within a wall or ceiling cavity. The cooled air is normally discharged directly from the enclosure, although it can be delivered to a specific area via short ducting. The unit’s output is controlled by cycling the fan, by varying the fan speed or by throttling the flow of water through the coil.
There are two main types of chilled beam: passive and active. A passive chilled beam provides room cooling by using natural heat convection. It comprises an overhead beam, mounted on, near or within a ceiling and containing chilled water from an external source. The area’s warm air continually rises to the beam, where it is cooled. It then drops back to floor level and the cycle is repeated. These are particularly appropriate for use at office perimeter zones, to cope with the solar gain. With active beams, a primary air supply is delivered to the beam, inducing room air through the beam. Active beams deliver a greater cooling capacity than passive beams, so that smaller or fewer units are required for a given amount of cooling.
Both methods have their potential advantages; if chilled beams were superior in every way, they would have completely replaced fan coils in new-build by now. Comparison between the two is complicated by the fact that a fan coil unit has a single function, while chilled beams can be integrated with other building services to create multi-service chilled beams, or MSCBs. These, accounting for a growing majority of chilled beam installations, can incorporate a wide variety of products within the beams themselves. Integrated lighting is typical, but cabling, control valves, sprinklers, sensors and security systems are increasingly commonplace.
One of the chief drivers of chilled beams’ popularity growth is the changing legislative and cultural environment. New regulations promoting energy efficiency — such as Part L2 of the Building Regulations, governing conservation of fuel and power — are leading to greater demand for water-based cooling. Such systems need less energy to provide the cooling requirement than cooling through the air.
Importantly, chilled beams operate with water at higher temperatures (14-15°C) than that used in fan coil systems (around 6°C). Having higher flow temperatures means that there is greater scope for a chiller circuit to run in free-cooling mode. This reduced need for mechanical cooling delivers improved energy efficiency. Fan coils are becoming more efficient, through greater use of DC motors with electronically commutated fans and raising the chilled water temperature to around 8°C, but this still leaves them less ‘green’ than chilled beams of equivalent output.
In addition, indoor air quality is of growing relevance, with clients demanding better working environments for their staff, as a driver towards to higher productivity and reduced absence levels.
A major factor in the shifting market, however, is the gradual disappearance of inaccurate preconceptions about chilled beams, chiefly concerning cost and flexibility. While acknowledging their popularity elsewhere and generally accepting their low running costs, UK specifiers had considered chilled beam systems as expensive to install. This meant that the capital cost had deterred specification of chilled beams for ‘normal’ projects. They had tended to be considered only for such major clients as banks and blue-chip companies, despite offering a lower life-cycle cost than four-pipe fan coils and other alternative systems.
These perceptions had arisen because of the way in which systems had been specified. Designers of such spaces as open-plan offices had tended to minimise costs by opting for 4 kW to 6 kW fan coil units. To supply an equivalent cooling load would normally require three or four chilled beams for every fan unit. In such a case, the initial costs solely for the units would be two to three times higher. This overlooked a potentially significant saving available with chilled beams.
Fan coil units typically require more complex control systems than those for chilled beams, which function in a different way. Firstly, chilled beams tend to self-regulate. When the load in the space rises, the difference between the air temperature and the mean water temperature increases which, in turn, increases the amount of cooling output produced by the beam. Equally, when the load in the space drops, the cooling output decreases accordingly. In addition, changes in room conditions tend to occur far more slowly with chilled beam systems, so there is no real benefit to having modulating valves on the pipes. A simple two-port valve system is perfectly adequate for most chilled beam systems.
In individual offices or hotel bedrooms or similar more confined areas, chilled beams can be considered as an alternative to fan coil units at a much reduced 1:1 ratio, offering significant capital savings. In such cases, using beams delivers an additional benefit to occupants, ideal for the application, of providing a virtually silent system with no draughts. Whether the application is for large or small spaces, initial costs can be greatly amortised through the use of MSCBs, incorporating other services within a single fixture.
Flexibility has been an issue for designers and specifiers, particularly within open-plan areas which are created with a view to future reconfiguration of the space. Fan coil units have been perceived as a more flexible system, because they allow the re-siting of diffusers to suit partition layouts. Here, the advance of technology has been critical in driving a re-evaluation of chilled beam capabilities.
A combination of Fläkt Woods ‘Comfort Control’ and ‘Flow Pattern Control’ means that chilled beams can now also be adapted to suit any potential partitioning of an open-plan area. Comfort Control is a unique function in which the air distribution from a chilled beam can altered within a matter of seconds, ranging from 100%-0% to one side, through 50%-50%, to 0%-100% to the other side. Flow Pattern Control is a device that can alter the flow pattern of the air leaving the chilled beam, enabling users to direct air away from corners or other obstructions which may divert it. Combining the two technologies enables the installation of chilled beams with an extremely high level of flexibility.
Finally, the implementation of chilled beams was previously hindered by their being regarded as more complex than fan coils. Fan coil units were seen as an off-the-shelf solution, while widely varying office layouts and customer requirements meant that chilled beams were viewed as needing to be bespoke systems. Such views are now disappearing, as designers and specifiers become more familiar with chilled beam systems and their benefits. There is also more widespread appreciation that the level of expertise on offer from the more experienced manufacturers represents an easily available resource which can be exploited at an early stage of design for the clients’ benefit.
In summary, the air conditioning market is increasingly driven by consideration of energy consumption and workplace air quality. In both cases, chilled beams offer a better solution than fan coil units. With traditional misconceptions concerning costs and flexibility being swept aside by improving design and better understanding, the recent trend away from fan coil units is likely to continue for the foreseeable future.
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