The future of refrig­er­a­tion, air condi­tioning and building systems

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.

Figure 1: In spite of the inte­grated commu­ta­tion and actu­a­tion elec­tronics, the new EC motors (on the right) are just as compact as conven­tional AC motors (on the left), thus permit­ting simple mechan­ical exchange.

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

Figure 2: Mechan­ical compat­i­bility: The new EC motor (on the left) can be attached in exactly the same way as stan­dard AC motors (on the right).

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.

Figure 3: Compact elec­tronics, encap­su­lated stator and rotor.

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

Figure 4: Air curtain: The blowers are constantly in oper­a­tion; a consid­er­able amount of energy can there­fore be saved by switching to EC motors.

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.

Figure 5: EC fans, opti­mised for use with evap­o­ra­tors in cold storage areas.

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

Figure 6: Venti­lated facade systems with EC centrifugal or tangen­tial blowers.

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.