Although chilled beams are grabbing a bigger share of the comfort air conditioning sector, fan coil units have been the first choice for developers of large City-based office blocks for decades. Terry Farthing, head of communications at Trox UK, gives his thoughts on the system and its future
THE ubiquitous fan coil unit is something of a Cinderella system – out of sight and out of mind. However, taking it for granted could leave you severely out of pocket.

Fan coils are a well established terminal system for controlling room temperature. Most are installed in ceiling voids with flexible or rigid ducting serving a number of terminal outlets in the form of slot, swirl or louvre face diffusers. However, most of the time, these separate components are sourced from different manufacturers.

Market research conducted by Trox suggests that 53% of consultants in the UK have had noise problems with fan coil units. The same research found that for any major project, 79% of consultants would require a mock-up test before specifying particular products. Such a test carried out at BSRIA could cost £15,000 to £20,000.

Trox has addressed these problems by implementing a system engineering approach. This means that fan coil units and diffusers are provided from a single source, with guaranteed noise levels, thermal performance and air distribution.

In a bid to demolish the scepticism associated with the over-optimistic claims made by some fan coil unit manufacturers, Trox has invested £150,000 in a dedicated fan coil unit test chamber and a further two air distribution test cells at its Thetford, Norfolk, factory.

Accurate fan coil unit testing can demonstrate that equipment will do precisely what is claimed, minimising risks on projects and offering peace of mind to the client as well as helping to develop the best solutions for particular projects.

Trox’s test facility that complies with the tough demands of BS4856 Part 1 1972 Methods for Testing and Rating Fan Coil Units, Unit Heaters and Unit Coolers, and Eurovent 6/3-1996 Thermal Test Method for Fan Coil Units.

The chamber can test thermal output and air volume performance of four-pipe fan coils with cooling and heating capacities of up to 6kW, and airflow rates between 50 and 500 l/s. Both horizontal and vertical units (with or without ducting) can be tested.

Future issues

Airside fan coil units are very popular and account for around a quarter of the UK market with two basic designs available. The inlet or outlet damper options utilise an arrangement of dampers/flaps to divert air through heating, by-pass and cooling zones to control the temperature output.

The carry-over or potential energy loss with some airside fan coils can be in excess of 500W in the bypass position.

The new airside fan coils developed by Trox significantly reduce this energy loss and in general operation could be claimed to be negligible and also meeting the new Part L requirements.

There is however opinions in the market place that suggest airside units will reduce in popularity in favour of waterside units.

Another new development being pioneered by Trox is the use of waterside variable air volume fan coil units (VAV/FCU).

Up until now fan coils have been constant speed, constant air volume. In other words the fan in the unit is on full-speed all day irrespective of cooling/heating requirements.

By utilising a variable air volume fan coil system, the motor speed can be varied by the building management system. Only a small speed reduction of 20% would cut in half the energy consumption from the fan motor. On a building of 10,000m2 with 400 fan coils this could equate to an energy saving of £15,000 to £20,000 per annum. With the development of these energy saving ideas, fan coils could hold on to its current market share. However there are compelling arguments for chilled beams so it will be interesting to see what happens over the next two years.

Market Facts and Figures:

• Total market size for chassis fan coil units is £30m

• This represents a total number of approximately 70,000 units

• The market has reduced by 25% in the last 4 years

• Airside fan coil units represent approximately 25% of the total market

Trox UK

01842 754545