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Fan coil units


he two leading chilled water terminal devices are fan coils and chilled beams and there have been a number of claims and comparisons made between the two options, many of which I believe have been misleading.


If the chilled water is supplied at elevated


temperatures, say 14°/17°C to both systems the main differences in energy usage are:- a) Fan coils have motors, chilled beams don’t. With EC motor designs specific fan powers SFP below 0.15w/l/s can be achieved and therefore the energy required is very low, less than 0.3watt/m². b) Chilled beams need more pressure to effect good induction which means the SFP of the main air han- dling plant is increased. This extra pressure means additional power is required which is not dissimilar to the total fan motor power of the fan coil units. Therefore at these conditions the comparison between the two systems is carbon neutral. If the chilled water temperatures are changed to, say, 10°/14° for fan coils and 14°/17° for chilled beams then there is a small difference in energy consump- tion between the two systems. By utilising variable air volume fan coils this difference can be reduced to around 3% .


The Advanced Air fan deck with large horizontally mounted fans


Fan coils vs chilled beams T


High induction slot diffusers and swirl diffusers were developed to improve the comfort levels in the occupied space. The high induction meant that the air distributed from the diffuser was mixing with the room air at high level providing low velocities and temperature gradients in the occupied areas which in turn led to increased comfort levels. With fan coil units the fan is able to propel the air through these high induction devices but with chilled beams this option of air diffusion is not practical.


Cooling/Heating


Most of the fan coils are supplied for heating and cool- ing, whereas virtually all chilled beams are cooling only. The main reason is that with only the primary air inducing room air, stratification may be prevalent on the heating cycle. This is why most designers specify- ing chilled beams would add low level perimeter heat- ing which is separate from the beam. The fan in the fan coil system can create a positive airflow over the heating coil, thus avoiding stratification.


Cost


With carbon emissions similar the cost of the prod- uct and system will be a major driver. Here the fan coil can have an advantage in both product cost and installation. Fan coils have been one of the leading terminal sys- tems for over 50 years. They are versatile and can be adjusted to change performance in situ. This flexibility in a range of performances from one size of unit adds to their appeal to designers. There is also a wealth of experience in both contracting and designing with fan coil systems. Recent advancements in fan coils means that their popularity is on the increase. Take for exam- ple the universal truly reversible concept Advanced air have recently introduced It is true on most projects the handing of the fan


coils is not finalised until late in the design process and manufacturers cannot commence the produc- tion process without this information. With this truly reversible and universal fan coil orders can be ac- cepted without the handings and the production process can commence. This is particularly helpful on fast track programmes where handings may not have been finalised until days before deliveries have to be made. Advanced Air can commence manufac- ture and even finish the fan coil unit without the handings. Changing the handing of the unit only takes a few minutes in the factory and can be under- taken on site by the contractor or specialist fitters. A universal coil means that it can be easily removed, rotated through 180°, the heating coil section moved and the new coil assembly quickly refitted with the new handing arrangements. BSRIA recently published figures taken from man-


ufacturers returns and has the fan coil market at around £30m with chilled beams just over £6m. If you look at the market sizes a few years ago they were similar. • Andrew Sergeant is the general manager of Advanced Air


Andrew Sargent


Andrew Sargent explores why he believes fan coil systems outperform chilled beam systems Indoor Air Quality


Spatial flexibility


With speculative office buildings forming a major part of the market, flexibility for the developer means that letting space is much easier with fan coils if partitions are moved and the system needs some modification. This can easily be carried out in the ceiling void with the worst case scenario being that blanking/moving/activating diffusers as required. With chilled beams it can be difficult to change them and partitions normally have to be erected in pre-determined positions.


 February 2017


www.heatingandventilating.net


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