Fan coils have maintained their position as the most popular terminal system for more than four decades, but the technology has, over that time, enjoyed little in the way of innovation. Now, with the introduction of tough new energy requirements under Part L of the Building Regulations and the growth in sales of multi-service chilled beams, pressure is building on fan coil manufacturers to introduce innovations to ensure the continued popularity of this system.

However, a lack of innovation is not the only challenge facing the fan coil sector. There is also a perception among many that much fan coil sales information, particularly relating to performance, is unreliable and that many buildings have been supplied with noisy fan coil systems.

So, if fan coils are to maintain their popularity, changes must be introduced in the form of:

•         Urgent product development.

•         Greater performance guarantees.

•         An overhaul of the way fan coils are designed, specified and procured using a “complete system” approach.

PRODUCT DEVELOPMENT

With a conventional fan coil system the motor always runs at the same speed irrespective of whether the room needs to be cooled, heated or is at design temperature.  Whilst constant air volume has the advantage of constant sound level and no air dumping from the diffuser it has a major disadvantage of  consuming  more  energy   than is required.    EC  motors  are   becoming increasingly popular, but instead of running at a constant speed greater savings will be achieved by adopting variable air volume (VAV) principles. If the air volume for each fan coil was reduced from 100% to 80% (a small reduction in air flow and barely discernable to the room occupants) the motor energy would, based on The Fan Laws, be reduced by 50% - a significant saving in power.  If the air was reduced from 100% to 60% there would be an 80% reduction in motor energy.

With a typical office building calculations can be made to provide an answer as to how much energy can be saved.  Taking a load profile for a typical zone by having VAV fan coils a saving in motor power of 75% is achieved.  Related to Watts/m² this would reduce power consumption down from 4.5 W/m² to 1.1 W/m²

PERFORMANCE GUARANTEES

TROX has undertaken extensive market research from which we have established the pros and cons of fan coil units and these are summarised in the box “Advantages and disadvantages of fan coil units”.

However, engineers have experienced noise problems from fan coil units and three quarters of the engineers interviewed by TROX said they would test the fan coil units for major projects.

BSRIA product testing specialist Phil Stonnard agrees that there is a problem with fan coil performance figures. He has said: “From its extensive experience in fan coil testing, BSRIA have found that some of those products had the performance which is 25-30% down on catalogue data.”

We therefore need to look at the overall system in terms of duct design, joint scheduling of fan coils and grilles/diffusers, with a view to offering guarantees on performance. This will take away the concerns of designers and minimise their risks when designing fan coil system

COMPLETE SYSTEM APPROACH

To improve the confidence of consultants still further, I believe there needs to be a total change in the system of design, specification and procurement where all the components within the fan coil system – diffuser, plenum box, fan coil unit and associated controls – come from a single source.

Starting with the original design, a system approach will ensure the best possible solution is developed. This will also allow for project cost savings by value engineering, off-site fabrication, and pre-commissioning of units.

Offsite fabrication will, I believe, become more prevalent due to the shortage of skilled site labour, improved build consistency and efficiency in the factory, and reduced installation times and increases fast track programming. “Just in time” delivery of factory-finished assemblies will streamline the construction process.

The benefits of factory prefabrication and pre-commissioning include:

•         Fan coil controllers can be factory set for design air flow and pressure independent modulating water valves can be factory set for design water flow.

•         Cost – Construction costs are significantly lower because the construction process is faster, there is a reduction in the number of trades, and the process is more predictable, of higher quality, less wasteful and safer.

Besides, a single point responsibility makes performance guarantees more easily available because of this focus on one manufacturer.

So, to summarise, I believe fan coil units are at a crossroads. They face mounting competition from other technologies and faith in their performance figures has suffered a series of hammer blows.

However, provided sufficient care is taken with how fan coils are developed, how they are tested and how they are specified, I see no reason why fan coil units should not only survive, but thrive.

BOX 1

Benefits of VAV fan coils

Fan coils that use VAV technology offer a range of benefits. For example, they are:

•         Energy efficient compared with constant volume units.

•         Exceed the requirements of the Building Regulations and reduce carbon emissions.

•         Have a lower specific fan power because of their high motor efficiency.

•         Capable of efficient speed control

•         Able to demonstrate lower maintenance costs due to longer bearing and motor life.

•         Easier and quicker to commission

BOX 2

Advantages and disadvantages of fan coil units

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