Swiss Rotors Stepper MotorEnergy recovery wheels are now established as a central part of the heating, ventilation and air conditioning (HVAC) industry. They are one of the industry’s most effective energy recovery devices, capable of transferring sensible (heat) energy, latent (moisture) energy or both from a building’s exhaust airflow into its incoming air stream. By completing the transfer of energy, energy recovery wheels reduce the amount of supplied energy needed to cool or heat the incoming air and consequently reduce a building’s overall energy costs.

The green credentials of energy recovery wheels are one of their biggest selling points. But environmental reasons are not the only issues powering the success of ERWs. With energy recovery efficiency levels approaching 90%, the world’s leading energy recovery wheels are undeniably effective in driving down energy costs. ERWs typically make large enough financial savings in their first three years of operation to cover the expense incurred in their installation. However, the typical lifespan of a modern-day energy recovery wheel is more than 20 years. So the potential for building owners to save money is both significant and long-term.

Enduring financial gains and positive environmental impacts are results well worth celebrating. That they are achieved with such a relatively straightforward piece of engineering is even more remarkable. Understanding how an energy recovery wheel works is neither complex nor difficult. Exhaust and incoming airflows are constructed adjacent to each other. The energy recovery wheel is positioned so that it rotates through both airflows. As exhaust air leaves the building, the energy recovery wheel captures the energy it contains, then rotates and transfers that energy into the incoming airflow. The alternating airflow direction also means devices such as the Swiss Rotors energy recovery wheel are self-cleaning and frost resistant at low temperatures.

What factors influence the ultimate performance of an energy recovery wheel?

Like any piece of successful engineering, today’s energy recovery wheels rely on a combination of several different elements. Each of these components has the capacity to affect the performance levels of an energy recovery wheel. These factors include:

  • The type of porous surface used on the ERW to capture sensible and latent energy. Has the manufacturer used a highly-suitable desiccant coating such as a 3A molecular sieve? Or has it opted for a cheaper alternative that results in lower performance levels?
  • The construction of the wheel and its subsequent percentage effective area. Wheels built using segments, for example, have a lower percentage effective area than those constructed using smaller outer casings and mounts.
  • How airtight the wheel is. Even small leaks can have significant impacts on the overall performance of an energy recovery wheel.

But arguably the biggest single factor on the ultimate performance of an energy recovery wheel is the efficiency and reliability of the drive system – especially the motor. Without the motor, the wheel ceases to function. So ERW motors must be both durable and engineered to the highest possible standards. Motors in energy recovery wheels are critical to the device’s overall performance.

What variations are available in energy recovery wheel motors?

Motors are responsible for the continuous rotation of the energy recovery wheel. Without the motor, it is not possible for an ERW to successfully transfer sensible or latent energy from one airstream to another at the requisite quantities to make a material difference to a building’s energy performance.

Product designers and engineers generally choose from one of four popular types of motor when they are producing an energy recovery wheel. They are:

  • AC motors, which are electrical motors powered by an alternating current. Electrical windings in the stator of AC motors are supplied with alternating current. This has the effect of creating a rotating magnetic field. At the same time, a current is induced in the inside rotor to produce a second rotating magnetic field. Torque on the rotor is produced when the two magnetic fields interact. However, AC motors tend not to be used when variable speed is required, because their efficiency markedly drops if they operate outside of the peak efficiency point on their performance curve.
  • EC motors, which are brushless direct current (DC) motors controlled by external electronics. Like AC motors, DC motors use magnetic fields generated by an electrical current to power the movement of a rotor. Variable-frequency drives and electronic circuit boards are two of the most commonly used control mechanisms for EC motors. Being brushless offers a range of benefits. Users do not have to worry about sparks. EC motors have a longer life than many of the other types of motor on the market. And EC motors are also far smaller than AC motors, making them ideal for tightly-engineered devices where space is at a premium.
  • Gear motors, which are a combination of an electric motor and a gear train. Powered by either AC or DC, they provide high output torque but lower output speeds. They are ideally suited for moving large objects relatively slowly – such as automatically-opening doors, windscreen wipers and hospital beds. However, gear motors are not suitable for devices that need high speed and relatively low torque, so they are rarely found in fans or pumps.
  • Stepper motors, which are brushless DC electric motors that divide each rotation into a series of smaller steps, each equal in size to the others. Stepper motors are used in all of the energy recovery wheels produced by Swiss Rotors. The motor is positioned inside the rotor casing. Because each full rotation of the motor is divided into a number of equal steps, it offers precise control and the ability to stop the motor at any specific point. Our stepper motors can run at a wide range of speeds without reduction gearing. The control circuit is simple and low cost, and the motor provides excellent response in the start, stop, and reverse modes.

Finally, there are some recurring choices made in ERW motors. Inverter speed-controlled motors are often used in energy recovery wheels because they enable more precise control of the subsequent temperature of the incoming airstream after it has passed through the ERW. On the rare occasions that the indoor and outdoor climates align to such a degree that neither sensible or latent energy transfer is required from the exhaust air to the incoming air, the motor can be switched off completely. It is also worth noting that the motors used in energy recovery wheels are now so small that the energy they consume to deliver each wheel rotation is negligibly low. 

Swiss Rotors energy recovery wheel motors

Three different stepper motors are used in our SF and RT series of energy recovery wheels. All three have a shaft diameter of 12mm, operating temperatures of -40˚C to +40˚C, RPMs of 0-400 and frequencies (Hz) of 60.

  • A 2.4kg motor (85mm x 85mm x 67mm), offering torque power of 2.0Nm – 55W, is fitted in sorption wheels between 500mm and 1000mm, as well as condensation and enthalpy wheels between 500mm and 1200mm.
  • A 3.5kg motor (85mm x 85mm x 97mm), offering torque power of 4.0Nm – 110W, is fitted in sorption wheels between 1100mm and 1700mm, as well as condensation and enthalpy wheels between 1300mm and 1700mm.
  • A 5kg motor (85mm x 85mm x 156mm), offering torque power of 8.0Nm – 260W, is fitted in sorption wheels between 1800mm and 2400mm, as well as condensation and enthalpy wheels between 1800mm and 2400mm.

We offer silent and highly effective EC or AC motors. Our EC motors combine with an integrated variable-frequency drive to enhance the overall efficiency of our ERWs, which is a major advantage when it comes to complying with energy efficiency regulations. They are also available to suit a range of different electrical requirements, including 208-230/380/460V/3, 575V/3 and 230/400V/3 AC options and 0.37kW/0.51HP 230V/1 and 0.45kW/0.6HP 230V/1 EC options. Each is VFD-compatible and factory-wired with the necessary connector, and all motors are built with UL-recognized components and tested and certified for UL:1995.

Due to their reliability, size, efficiency and control, stepper motors are the most appropriate motor type for energy recovery wheels. Stepper motors are one of the key reasons why all of our energy recovery wheels are true market leaders and the best solutions available on the international market.