Electronically commutated motors bring a rethink of fan-coil units

With the application of EC motors, fan-coil units are given the potential to become a much more efficient, and controllable, method of air conditioning. Peter Lowther explains.The introduction, by Ability Projects, of fan-coil units with electronically commutated (EC) DC motors in 2002 represented a massive step forward in the technology of fan-coil units, bringing with it a number of significant customer advantages in terms of energy efficiency and controllability. Latterly, with production improvements and a new controller designed specifically for the EC product, Ability can offer its fan coil/controls package at the same price as any alternative using AC motors. Inroads The application of EC motor technology in domestic and commercial products such as heat-recovery units and boilers is already commonplace, and the use of EC fan motors in fan-coil units, with their attendant substantial reductions in energy consumption and running costs, is now making inroads into the UK commercial air-conditioning sector. The fact is, an EC fan-coil configuration can reduce electrical input by about 55%. On a large development this saving can add up to many kilowatts. A 2-fan unit selected at a typical duty point (2.4 kW cooling, 200 l/s at 30 Pa ESP and NR30) will consume 68 VA (apparent power) when fitted with EC motors, where previously it would have consumed 154 VA in AC form. The benefits of EC technology are maximised in the Ability Matrix EC fan coil system, launched in 2007, by not only providing infinite speed control of the whole unit but also of each separate fan in the fan-coil unit. Controlling each fan in this way enables each duct run to be balanced for air volume through fan speed alone, a feature unique to Matrix. There is then no need for costly volume-control dampers within fan-coil ductwork — avoiding the noise they generate, the energy they waste, the time they take to install and commission and the health hazard they can represent. Matrix precisely balances the air volume down each of the duct runs by controlling the fans at the correct speed, rather than throttling back over-performing ones. Historically, fan-coil installations are designed for single-speed operation and are invariably run with a fixed air volume, thermal output being controlled by water volume alone. Matrix, however, is also designed to adjust the overall air volume based on either occupancy, thermal demand or a combination of both. The design speed must obviously be sufficient to deal with peaks in summer, although for most of the year they are not actually experienced. Matrix follows demand and occupancy, adjusting the air volume (and, conventionally, the water volume) to meet that requirement and no more. Thus, if a meeting room or similar area is empty, the fan coil can operate in set-back mode. When a person enters, the unit increases its fan speed just sufficiently to compensate for the marginal increase in demand. If even more people enter, the fan speed rises further, but, once again, only enough to meet the load. Conversely, of course, when people leave the room, the unit returns to its set-back mode. Reduced energy consumption With fan speeds controlled according to demand, a Matrix fan-coil unit in set-back mode could consume 20%, or even less, of the electrical input of the equivalent AC unit. Lower speeds reduce energy consumption considerably and also reduce project noise levels. The Matrix controller also monitors the air temperature off the coil. If this temperature deviates from user-definable settings any programmed strategy for controlling fan speed is automatically overridden to pull the air off temperature back into line.
Using an electronically commutated motor in each duct off a fan-coil unit enables the precise airflow required to be delivered, without energy-wasting and noisy volume-control dampers.
Fan-coil units with EC motors naturally run cooler than those with AC motors. A certain amount of heat is generated by the motor, which adds to the cooling load on a fan-coil unit, which must provide some cooling simply to overcome motor heat even before it begins to cool the host building. Matrix EC fan/motor units give off far less heat, a reduction of around 85% — or from roughly 65 W to 10 W per motor. The vital extra component in the Matrix system is its BACnet open-protocol intelligent fan-coil controller, factory pre-wired to the fan-coil unit and complete with accompanying dedicated software. Developed specifically for Matrix, the controller not only incorporates all the usual facilities such as modulating valve control and on-coil temperature sensing but also now gives users wireless, laptop access to all unit features and settings without requiring access to the ceiling void. Fan speed, air volume balancing, set points etc. are all controlled by and set using the supplied software. Another great advantage is that on projects with multiple fan coils installed in the same physical style, these instructions, particularly those concerning air volume balancing, can be ‘electronically copied’ from one unit to another, or even from one floor to another. This wireless link, accompanied by the fact there are no volume-control dampers in the ceiling void, minimises any damage to the ceiling structure and any occupant disruption that may be caused during commissioning. The energy-efficiency improvements in Matrix fan-coil systems stem from the EC motors and the intelligent BMS controllers with the wireless technology they employ. This has enabled Ability to re-evaluate the raison d’être of fan coils and integrate these new technologies into a complete package. Thus, the fan-coil chassis has been modified, the latest fan technology applied, the control strategy re-evaluated from first principles and the whole package overlaid with the flexibility of wireless communication. Longer life As an additional benefit, the EC Matrix unit has an expected working life approaching double that of its AC equivalent — potentially 30 years instead of the more normal 15 to 20. Finally, Matrix represents an energy efficient, innovative fan-coil system that will often cost no more than the standard inefficient AC fan-coil system currently employed. The Matrix system rejuvenates the humble fan coil and shows the way forward for air conditioning with a product fit for the 21st century. Peter Lowther is managing director of Ability Projects Ltd.
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