Fan coil units are a mature technology, and yet there remains room for development - if not in the product itself, then certainly in its control, as Peter Lowther explains
Somewhere close behind aeroplanes, cars and cows, air conditioning has been identified as one of the prime energy-consuming contributors to the global warming effect. Ironically, however, and whether right or wrong, it seems likely that air conditioning will turn out to be one of the beneficiaries of the same effect.

The problem is that we have grown used to our creature comforts and, global warming aside, we are not in reality going to give them up. The way forward for the air conditioning industry, as clearly seen with other industries, must be to ensure that the products we are familiar with are able to provide the same levels of comfort, well-being and prosperity we wish for, but in a far more energy efficient way.

How many times do we hear nowadays: 'I have just bought a new car? Did I consider the option of doing without a car altogether? Of course I didn't! But I did pick a model with consumption figures that are far superior to the same type of five years ago.'

Increasing demand for ac

The same situation applies to air conditioning systems. Global warming, whether it is partly created by air conditioning or not, must in itself increase the demand for products from the air conditioning sector. Our customers however, will rightly demand - and their product choices will be wholly dependent upon - how efficiently we can meet their rising expectations.
Product styles and manufacturers that aspire to this challenge will be rewarded. Those that don't will go the same way as the gas-guzzling Hummer.


Fan coil units have remained fairly constant in concept over the last 25 to 30 years; a few cosmetic changes, maybe, but nothing to write home about. The first substantial advancement was the introduction to the market in 2002 of far more efficient EC (electronically commutated) fan and motor sets.

Frankly, this development threw fan coils an energy efficiency lifeline in the nick of time. Now, some years later, fan coils using the EC motor/fan technology have become the 'rule' and their old AC counterparts the (vary rare) exception. But, EC motors aside, fan coils remain ostensibly unchanged; that is, a fan and a coil in a box.

Keep the product moving

To keep fan coil units at the forefront of viable energy efficient systems has required - and will continue to require - that we keep the product moving. The problem is that a fan coil is still simply a fan and a coil in a box and so, at face value, further development would appear to be limited.

In fact, this could not be further from the truth. The future development of fan coils lies not in the actual product, but in the control systems or control methodologies that define the manner in which the product behaves.

This has already been achieved in a limited way with the introduction of variable air volume (VAV) fan coils and occupancy dependent fan coils. These units exploit the infinitely speed controllable capability of the EC fans such that not only does the water volume to the heat exchange coils vary with demand, but similarly, the fan speed.

VAV strategies monitor the demand and control fan speed, taking advantage of the fact that for most of the year, the real time thermal demand and air volume requirement represent only a small percentage of the calculated peak condition the system was designed and selected to meet.

Some concerns have been voiced about varying the air volume from fan coils giving rise to dumping, variable throws and draughts, but these can all be overcome and represent a small price to pay for the extra efficiencies these units bring.
The second most commonly applied strategy allows these units to look for and exploit the fact that office spaces are often left unoccupied for long periods. During these periods, EC fan coil strategies are able to adopt a set-back or 'sleep' mode, thereby saving more energy.

An EC unit in a meeting room, for example, can be pre-programmed to widen its thermal dead-band when the room is unoccupied; effectively keeping the unit and the space in a thermal and energy consumption 'tick over' state. Then, when an individual enters the room, the widened dead-band snaps back into normal mode and the unit reacts accordingly, but only if required.

The unit strategy continues to monitor occupancy and demand and sets its water flow and air volume to meet the need and no more.

So where do fan coils go from here? After all, if development does not continue, fan coils will fade into obscurity to the obvious advantage of alternative air conditioning concepts.

One important new development in this respect is the introduction of self-commissioning fan coil units. These units bring advantages to contractors and designers in terms of their installation simplicity, whereas previously, the only group to really benefit from EC technology was the user or owner paying the bills.

Self-commissioning fan coil units also use the intelligence inherent in the EC motor to allow the adjustment and in certain instances the self-adjustment, of the fan speeds of fan motors providing air to different ducts via a single fan coil.

This removes the need for volume control devices (VCDs), which, until now, could only be described as a necessary evil. VCDs cost money to buy, install and set, they regenerate noise and they throttle the very air movement that someone has paid good money to create.

Self-commissioning fan coils can also incorporate two-port pressure independent and characterised control valves, either removing the need for (or at least reducing) the time required for water balancing on site.

New to the market

These types of valves can be either physically set at the valve itself or set and adjusted through the BMS network. It has to be admitted that these valves are new to the market and are creating something of a stir since they challenge conventional water balancing methodologies.

However, they are inherently a good money- and time-saving product and will, when they are better understood (and perhaps some more development work is done), become the norm.

So, with the combination of self-commissioning, variable air volume and occupancy dependant strategies, the problem of 'where now for fan coils' has been addressed.
Only time will tell but the one thing that is certain is that fan coil development will continue and fan coils will always remain as one of the preferred air conditioning options.