Chilled beams versus fan coils

The growth of the chilled beam market accelerated from 2000 – 2008 but what will happen in the next few years to this system with the introduction of ECM smart motors and Variable Air Volume (VAV) to fan coil units?

With any forecast or predication it is always worth studying what’s happened in the past since invariably this will give a clue as to how things will develop in the future.

Chilled beams had lower carbon emissions than fan coils and this was a driver due to the impact of the then new building regulations. This started to have a significant influence on the type of system chosen. The focus on carbon emissions intensified which led to dramatic increases in the demand for the chilled beams and by 2007 the market had reached a value of around £30m mostly at the expense of fan coil systems.

Our own market research suggests the following markets sizes/values:

Note the significant changes from fan coils and VAV to chilled beam options.

Fan coil systems have been around for a very long time and have been the system of choice globally. In the UK they have been extensively used and are the preferred system for many major developers and consultants. They hold the number one spot as the most popular terminal air conditioning system from the 1960’s and are still at the top in terms of building area conditioned by this system.

New developments

Since 2008 EC Motors have become a popular option with fan coil units and research at Advanced Air has shown that a Specific Fan Power (SFP) of 0.15w/l/s can be achieved, reducing the carbon emissions by a figure approaching six times that for a conventional AC fan coil unit. This has totally changed the carbon emission argument because now there is little difference between chilled beams and single fan EC fan coil units.

It is however important to differentiate between the multiple EC fan deck and the single EC fan. Figure 1 shows a conventional EC fan deck where a number of fans are utilised (up to a maximum of five) with each impeller having their own dedicated motor. This multi fan deck arrangement evolved because initially the European EC motor supplier had only one size of motor which was 75watts

Figure 2 shows the version that Advanced Air developed with a single much large EC motor (250 watts) sourced from the USA and the fan deck turned through 90 degrees or horizontally mounting the fan. The result of this was a slower speed, more efficient fan. Both these factors contributed to the very low SFP of down to 0.15w/l/s. This has resulted in a negligible difference in carbon emissions between a building using chilled beams and one using fan coil units.

So now that the carbon emissions issue has been all but neutralised in the comparison of the two systems, what are the other issues that effect their selection and how does each systems compare?

Capital cost

After energy, capital cost is probably the next most important issue (in fact in many cases this is incorrectly put ahead of the energy argument). The cost comparison of the product only shows that chilled beams are over twice the cost of a fan coil unit with the same cooling capacity.

With a simple chilled beam mounted in the ceiling, other costs over and above the product will be installation, piping, ducting, controls and electrical works. A similar range of additional costs would also apply to the fan coil system.

Having completed this exercise our calculations show that there can be significant cost savings when utilising single fan deck fan coil units compared to ceiling mounted chilled beams.

Flexibility

With speculative office buildings forming a major part of the market, flexibility for the developer means that letting the 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 and the worst case would be moving and activating diffusers as required. With chilled beams it is a major problem to change them and partitions normally have to be erected in predetermined positions.

The fan coil can also cope with a much wider range of cooling loads and be installed with extra usable capacity which further enhances its flexibility.

Comfort cooling

Effectively a chilled beam will move 30 to 40% more air around the space for the same cooling load. What this does is limit the cooling capacity of a chilled beam to 120w/sq m while still providing comfort cooling. In comparison a fan coil unit can be connected to a more superior air distribution device such as a swirl diffuser and room loads in excess of 200w/sq m can be dealt with while still maintaining comfort conditions.

Multi service

With flush mounted units the chilled beam can be multi service as can the fan coil system by using integrated service modules. However with an exposed installation multi service chilled beams are the only viable solution. These are utilised in older buildings where the slab to soffit heights will not allow a false ceiling to be installed.

Heating

Virtually all fan coils are supplied as 4 pipe heating and cooling units. Chilled beams are normally supplied in cooling only with low level heating coming typically from trench heating which can add to the cost and reduce the letable space. With the air being propelled by fans it is easier to avoid stratification and introduce an early morning boost if required.

The future

As will be seen from this article it was the energy argument that was the main market driver for the success of chilled beams. Now that has been all but neutralised the issues mentioned above will come into play.

Fan coils score well on capital costs, flexibility and high level heating. Based on these facts I believe that fan coils will go from a popular system to the preferred system in at least 70% of the projects. As such the market will grow and assuming that market size is the same as in 2007 I would forecast that fan coils will reach a market size of £45m and chilled beams £15m, which is a 50% increase for fan coils and a halving of the market for chilled beams.

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