Society is facing considerable challenges in the light of global warming and world population growth. And so the top priority has to be to reduce energy consumption. According to the WHO there is a direct correlation between world population growth and water consumption, the number of motor vehicles, increasing CO2 emissions and the demand for electricity. In this context the concept of “efficiency” takes on major significance with a view to accommodating a good deal of the extra energy demand in the future. In the field of refrigeration, air conditioning and building systems, the use of energy-saving drive units for fans and blowers can make a great contribution to such efforts.
The influence of energy-saving fans on energy consumption and CO2 emissions can best be illustrated by a concrete example: Use is frequently made of asynchronous motors as drive units in refrigeration, air conditioning and building systems. These AC motors are of simple, compact design as they take their supply directly from the AC or three-phase AC network. They do not require any mechanical commutators or electronic components for supplying the rotor. They are both robust and reliable. Their one major drawback is however their comparatively poor efficiency. Particularly in the part load range this is clearly inferior to that of EC motors, which operate at around 70% efficiency. This does of course have an influence on power consumption in virtually all applications.
An impressive set of figures
The size 68 AC motor for example, widely used in all manner of applications, provides a very clear example to illustrate the point: Looked at over the past five years and assuming an average power consumption of 150 W and a duty cycle of 75%, the annual energy consumption of the around 25 million AC motors of this type employed as fan drive units in various applications was not far short of 25 TWh (= 25,000,000,000 kWh). That represents more than twice the output of the Neckarwestheim II nuclear power station, which produces about 11.5 TWh per year. Or to put it another way, at least two nuclear power stations are necessary to supply the AC motors used in a five-year period in various fan applications in refrigeration, air conditioning and building systems.
“AC to EC” – exchange made easy
It is essential to save some of this energy in the future – and it can be done. Thanks to the development of a new series of EC motors, ebm-papst Mulfingen is now in a position to replace conventional AC motors with highly efficient EC technology with the same mechanical design. It is basically the same process as for old 100 W bulbs. These can replaced by energy-saving lamps which fit in the same holders. The development of EC motors mechanically compatible with AC motors and their extremely compact design does however represent something of a technical challenge.
The EC motor concept is based on synchronous motors with permanent magnet excitation. The magnetic rotor operates in synchronism with an electronically generated rotating field. This makes it possible to achieve any required operating speed irrespective of the mains frequency concerned. Accommodation of the electronics required for EC motors in a confined space (Figure 1) demands a lot of experience and expertise. Mechanical compatibility was also necessary in addition to the miniaturisation and optimisation of the electronics. This included employing the same type of mounting flange as for AC motors (Figure 2) for example, as well as modification of the motor design as a whole.
Good heat dissipation, high degree of protection and sustainable design
The results are impressive. The new compact EC motors are based on the successful external rotor principle in which the rotor rotates about the internal stator. A number of practical advantages are gained from the thermoplastic encapsulation of the laminated core of the stator. The high-grade plastic material provides excellent electrical insulation and it is possible to integrate the ball bearing mount. This permits variation of the wall thickness and spacing, making it easy to compensate for laminated core tolerances for example. Finally, the entire wound assembly is encapsulated in thermosetting plastic (Figure 3). The one-piece rotor moving around the stator is of optimum aerodynamic design. Air inlets in the rotor ensure ideal dissipation of the stator heat. In combination with the encapsulated stator the motors have a guaranteed high level of IP protection (IP54). Sealing of the electronics also plays an important role. In contrast to previously used concepts involving a flange and various O-rings, the electronics housing was provided with an elastic sealing component to ensure long-lasting protection of the electronics. The entire motor is robust and shock-proof whilst offering outstanding reliability and a long service life.
When designing and manufacturing the new EC motors, great emphasis was also placed on sustainability and the preservation of resources. This is demonstrated by a variety of details. For instance, the one-piece rotor with press-fitted shaft reduces the number of manufacturing steps and fewer parts are required thanks to the use of multi-function components. The heat dissipation concept and a relatively short core also help to reduce the amount of material. And less material means using less energy in manufacturing.
Convincing practical examples
The energy efficiency of EC motors is also associated with other properties which have a positive influence in everyday operation. These include speed control by way of the integrated electronics for example. The speed can thus always be matched to the given requirements. What’s more, EC motors are much quieter running than speed-controlled asynchronous motors on account of the noise inevitably generated by the triac or frequency converter control employed by the latter. Other advantages are the high power density, the compact size and the monitoring function which permits interrogation of operating data and statuses at all times.
A variety of applications already implemented provide ample evidence of the environmental, financial and practical benefits to be gained by swapping from AC to EC motors in refrigeration, air conditioning and building systems. One such application is the so-called air curtain. This involves blowers creating an air flow barrier, usually employed to separate warm indoor air from cold outdoor air. EC blowers (Figure 4) operate with outstanding efficiency and allow adaptation of the flow velocity to suit requirements, e.g. reduction when the door is closed, switching between winter and summer mode and day/night-time settings. The low noise level is a further positive feature.
This applies similarly to the evaporator unit fans used around the world in refrigeration systems, for instance to transmit heat in cold storage areas (Figure 5). As such systems operate with a high duty cycle, power consumption can be considerably reducing by employing EC motors. And the AxiCool range of EC fans designed specially for this sort of application has even more advantages to offer: They are able to withstand the harsh cold storage conditions, produce little heat in the refrigeration system thanks to the high level of motor efficiency and can be regulated to suit requirements.
Ventilated facade systems (Figure 6), which not only ensure the necessary exchange of air but also provide heating and cooling, are yet another example of successful conversion to EC motors. Further benefits include demand-based regulation and low noise at lower speeds. The compact design of the fans is just as important for today’s planning requirements as uncomplicated plug-and-play installation.
One nuclear power station less
There is no end to the list of possible examples, encompassing EC blowers in range hoods or clothes dryers, duct fans, fans in refrigerated display cases and a whole host of other applications. Common to all is a roughly 40% average reduction in power consumption on switching from AC to EC motors. Going back to the figures in our earlier example involving 25 million AC motor applications, here is another interesting thought: If all 25 million AC motors were to be replaced by EC versions and assuming a potential average energy saving of 40%, the annual saving would amount to nearly 10 TWh. The efficiency of EC fans in refrigeration, air conditioning and building systems would therefore permit an entire nuclear power station to be shut down. That would be an indisputable contribution to reducing future energy consumption.