Fan coil unit technology: EC motors

Oct 4, 2023

Back in July 2021, new EU ecodesign measures for electric motors and variable speed drives came into force across the EU. It introduced new standards for motors and drives aimed at improving energy efficiency. 

Motors and the ecodesign measures

The new rules updated previous regulations from 2009, setting out to broaden the scope and reflect the rapid pace of technological change. The new regulation includes motors with a power range from 0.12 kW - 1000 kW, and variable speed drives. Both motors and drives have to display their efficiency at different load points, in terms of speed and torque, in a bid to help designers and engineers optimise the efficiency of entire systems.

The updated regulations will make substantial energy savings, with European Commission modelling estimating annual savings of around 110 TWh by 2030 – the equivalent of the electricity consumption of the Netherlands and 40 million tonnes of CO2 emissions each year.

When it comes to HVAC, the ecodesign measures apply to motors powering a number of systems, including fan coil units. Electronically commutated (EC) motors, are fast replacing traditional alternating current (AC) and direct current (DC) motors because of their heightened energy efficiency.

The difference between AC, DC and EC motors

AC induction motors are powered by AC voltage. They use a series of coils (copper windings) in the stator field, to create a rotational electromagnetic field, which varies in strength and polarity.  A squirrel cage in the rotor field is induced by the stator (creating a magnetic field). These two magnetic fields interact with each other to make the rotor turn.

AC motors are designed to operate at a single speed in a specific point on a performance curve (at the peak efficiency of the motor). Outside of this point, there’s a significant drop in efficiency. Additionally, as AC motors induct current on the rotor, energy is consumed in the process, further affecting efficiency. This means of all the motors, AC units are the least efficient. 

DC motors are powered by DC voltage. They use permanent magnets in the rotor, and rely on carbon brushes and a commutation ring, to switch the direction of the current and magnetic field polarity in the stator windings. This creates magnetic attraction and repulsion forces, which rotates the rotor. 

Because DC motors use a magnetic field from permanent magnets, (rather than inducting current on the rotor) they can be 30% more efficient than AC motors. DC motors can also be run at variable speeds and offer more precise control. However, they can lose efficiency due to aspects such as brush friction and eddy-current losses. DC motors are also more prone to breakdown and have a lower operational lifespan, as the brushes can spark and will wear down with time.

EC motors achieve commutation electronically rather than mechanically. The motor combines AC and DC voltages, and achieves electronic commutation through integrated electronics. 

If you were to compare AC, DC and EC motors, you’d find EC motors the most similar to their DC counterparts. EC motors are essentially brushless, direct current, external rotor motors that combine best features from their AC and DC rivals. Crucially these motors offer additional functions such as speed control, pressure control, constant pressure and constant airflow. 

Of all the motors, EC units are the most energy efficient and offer reliability due to their brushless design. EC motors can also offer more precise cooling because they generate less heat. This means that less motor heat is absorbed by the cold air discharged from the fan coil unit.  

How do EC motors work?

EC motors will have the following components:

  • Rotor
  • Permanent magnets
  • Bearing system
  • Stator
  • Windings
  • Commutations electronics
  • Hall sensors 
  • Housing
  • Mains and control connections

EC motors are supplied by an AC voltage, which is converted to DC by a commutator. This is important because DC voltage offers more efficient energy performance compared to AC, and can offer variable speeds. Fashioned as a brushless DC motor, the stator (stationary part of the motor) is larger than in DC motors to enable the addition of commutations electronics including a PCB (printed circuit board) and rectifier, which switches voltage from AC to DC.

EC motors use permanent magnets and electrical windings to create a magnetic field. The commutations electronics direct specific amounts of electrical current, in certain directions, through each of the windings, depending on the position of the motor, direction of rotation and speed set point. This is perfectly timed to develop magnetic poles in the stator, which then interact with the permanent magnets in the rotor. 

Depending on the fan speed required, the appropriate magnets are attracted, in sequence, to the magnetic poles in the stator. Not every stator winding will be charged with the same polarity – to generate movement some of the stator windings will be positively changed, some will be negatively charged. This creates magnetic attraction and repulsion forces, which rotates the rotor at the optimum torque. A motor running at its idea torque (at all speeds) is running at its peak efficiency.

Because of the role played by the electrics to perfectly vary the application of current, very precise monitoring and control is achieved. This not only means that EC fans can run at variable speeds, but also that they are still highly efficient even when running as low as 20% of full speed. 

Additionally, although EC motors have a larger stator than DC motors, there is no need for carbon brushes or a collector. This means that overall, the EC unit is smaller and less prone to breakdown caused by wear and tear.

How much energy do EC motors save?

EC motors are highly energy efficient, with efficiency ratings exceeding 90% at 100% capacity. Even when running at variable speeds EC motors out perform their AC and DC counterparts, making them an excellent choice for fan coil units.

Additionally, EC motors can be retrofitted to increase efficiencies in existing systems. In fan coil units that are retrofitted with EC motors and recommissioned to reach optimum operation, real life efficiency improvements have been seen in the range of 46-82% at low speed, and 52-80% at high speed.

Benefits of EC motors

EC motors hold a number of advantages including: 

  • Highly energy efficient
  • Long service life
  • Less prone to wear and tear (brushless technology)
  • High degree of system monitoring and control
  • Full variable speed
  • Additional functions such as pressure and airflow control
  • Generate less heat – more precise cooling
  • More flexibility
  • Smaller size
  • Less noise
  • Longer bearing life 
  • Can be installed in any type of fan coil unit
  • Can be retrofitted to improve energy performance of existing systems
  • Can be cheaper to install than DC motors, as they do not require the installation of additional technology such as transformer control, frequency inverter, or phased angle control.

How to choose energy efficient fan coils

At Eurovent Certita Certification we certify the performance of a number of fan coil units that use EC motors. Certification makes it possible to compare independently verified products, because certified products:

  • Have their performance evaluated according to the same criteria, and the results are expressed in the same unit of measurement, regardless of the country where the products are manufactured or marketed
  • Have performance verified by an impartial, independent and competent accredited body
  • Comply with standards
  • Will work according to the specifications stated by the manufacturer.

View and compare fan coil units and other HVAC products in our certified product directory. 

Search for products now