RadiPac: An ongoing devel­op­ment process

The tech­nology involved with centrifugal fans for air handling units is constantly being enhanced – and not without good reason, given that users are demanding ever higher stan­dards in terms of control and energy effi­ciency. Legal stip­u­la­tions such as the EnEV (Energy Conser­va­tion Regu­la­tion) and the EVPG (Energy-related Prod­ucts Act), known in Germany as the Ecode­sign regu­la­tion, have greatly increased aware­ness in this respect (refer to “Ecode­sign” box on Page 7). At the same time, economic consid­er­a­tions are also an impor­tant factor in the light of the rising cost of energy. After all, the higher the number of fans in oper­a­tion, the more there is to be gained from energy effi­ciency.

Contin­uous improve­ment process

Fig. 1: The new-look RadiPac. The modi­fi­ca­tion work mainly concen­trated on the air inlet into the impeller, the posi­tioning of the external rotor motor in the impeller and the blade profile of the impellers.

ebm-papst, the motor and fan special­ists from Mulfingen, have long since been committed to a process of constant improve­ment which in the final analysis is of equal benefit to both the envi­ron­ment and the finan­cial inter­ests of the customer. For instance, the centrifugal fans of the RadiPac product range (Fig. 1, Page 6) designed specially for use in air handling units have been the subject of ongoing enhance­ment in recent years, with partic­ular emphasis on energy effi­ciency, noise reduc­tion and handling prop­er­ties.

State-of-the-art motors

Consid­er­a­tion was first given to the motors employed. In the case of the external rotor Green­Tech EC motors, recent devel­op­ments have included improve­ments to the actu­a­tion elec­tronics and the use of higher-quality stator plates to increase effi­ciency. The effi­ciency levels achieved by the energy-opti­mised motor, a mains-powered perma­nently excited synchro­nous motor (also known as BLDC or PM motor), are already far supe­rior to the values required by effi­ciency class IE4 as per IEC 60034-30. What’s more, these external rotor motors operate with “simple”, inex­pen­sive and above all readily avail­able ferrites. In other words they are not reliant on poten­tially prob­lem­atic rare-earth magnets and yet still manage to attain effi­cien­cies well in excess of 90% (refer to box “No depen­dence on rare-earth magnets”).

The successor: there is always room for improve­ment

Fig. 2: The results of the opti­mi­sa­tion process are impres­sive. All-in-all, modi­fi­ca­tion of the motor and the flow machine brought about an up to 10% increase in the effi­ciency of the size 400 RadiPac fan.

This product range is now never­the­less past its prime and – as already planned since 2010 – is being replaced by a successor model designed to set new stan­dards in venti­lation tech­nology. The prin­ciple of company founder Gerhard Sturm, that every inno­va­tion and enhance­ment should be better than its prede­cessor, has once again been success­fully put into prac­tice. Expe­ri­ence has repeat­edly shown that modern EC drives far surpass the conven­tional AC drives still widely used in air handling and air condi­tioning systems in terms of energy effi­ciency. It is however impor­tant not to forget that a fan always has to be viewed as a complete system made up of the impeller, motor, control elec­tronics and housing. So the enhance­ment process has to encom­pass all aspects – from the elec­trical connec­tion to the air outlet at the impeller and even the instal­la­tion situ­a­tion in the air handling unit – if the energy saving poten­tial is to be used to its best effect (Fig. 2).

No depen­dence on rare-earth magnets

Fig. 3: External rotor motor with Green­Tech EC tech­nology: The rotor moves around the wound stator rather than in it and does not require the use of rare-earth magnets.

In external rotor EC motors, the stationary part of the motor, i.e. the stator and coils, is located on the inside and the moving part, the rotor with the perma­nent magnets, is on the outside (Fig. 3). The external rotor moves around the internal stator. This arrange­ment in itself makes it possible to achieve a higher torque (magnet volume, air gap, radius) with an external rotor than with an internal rotor with the same length of core, the same magnet system and the same magnet thick­ness (reduced magnet volume, reduced air gap, smaller radius). By making clever use of the degrees of freedom in the fan area, an external rotor motor employing hard ferrites can attain torques and levels of effi­ciency which can only be achieved by an internal rotor with limited degrees of freedom (volume, mass) using rare-earth magnets. As opposed to servo drives, there is no need for fan oper­a­tion to be highly dynamic. On the contrary, a certain moment of inertia is desir­able to obtain smooth start-up and accel­er­a­tion char­ac­ter­is­tics. This means that it is no problem for Green­Tech EC fans to manage without rare-earth magnets and use can instead be made of ferrites which are not just consid­er­ably less expen­sive but are also avail­able at stable market prices on account of their avail­ability.