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Combining EC tech­nology with airfoil blades

In venti­la­tion, air condi­tioning and refrig­er­a­tion appli­ca­tions, designers and oper­a­tors often discover that the fans installed in their equip­ment are noisier or less energy-effi­cient than expected. The condi­tions of instal­la­tion are often to blame, as they can have a nega­tive effect on power consump­tion, air perfor­mance and noise emis­sions. The fan’s impeller, motor, control elec­tronics and housing are opti­mized for energy effi­ciency and noise emis­sion, and the actual condi­tions of instal­la­tion in AHUs should not be neglected.


Motor and fan specialist ebm-papst is putting consid­er­able effort into devel­oping the poten­tial of its prod­ucts. After estab­lishing itself in the market, the RadiPac series of centrifugal fans is now expanding, with new models in sizes from 630 to 1,000 (Fig. 1). Thanks to a number of aero­dy­namic improve­ments, all of the fans in this series work with a wide optimum effi­ciency range and also feature other prac­tical char­ac­ter­is­tics. With drive power from 500 watts to 12 kilo­watts and sizes from 250 to 1,000, air perfor­mance of up to 40,000 m³/h can now be achieved.

Rein­venting the impeller – with airfoil blades

Figure 1: Having estab­lished itself in the market, the RadiPac series of centrifugal fans is adding new models again. With drive power from 500 watts to 12 kilo­watts and sizes from 250 to 1,000, air perfor­mance of up to 40,000 m³/h can now be achieved.

The effi­ciency of the motors is already well above the values called for by the IE4 effi­ciency class. But greater motor effi­ciency is no guar­antee of an equally high overall system effi­ciency. Besides its motor, a fan’s impeller, its housing and even its condi­tions of instal­la­tion have to be consid­ered when analyzing the energy situ­a­tion, if all poten­tial for saving energy is really to be real­ized.

With this goal in mind, the engi­neers at ebm-papst have performed a complete aero­dy­namic opti­miza­tion of the RadiPac fans, focusing on the air inlet, the motor’s posi­tion in the impeller, the blade profile and the impeller air channel. They designed the inlet ring for the impeller and its aero­dy­nam­i­cally opti­mized blade channel. And they adjusted the motor’s posi­tion in the impeller to achieve a good compro­mise between compact­ness of the complete fan unit and the most aero­dy­nam­i­cally bene­fi­cial loca­tion for the motor in the impeller.

Figure 2: Starting with size 310, the impellers have the new airfoil aluminum blades for improved effi­ciency. The flow diagram at the right shows the pres­sure distri­b­u­tion; low pres­sure is shown in blue and high pres­sure in red.

The airfoil aluminum blades in the impellers result in greater effi­ciency (Fig. 2). The RadiPac Airfoil impeller is now both lighter and stiffer. They achieved a further reduc­tion in the pres­sure losses at the inlet and also improved the outflow char­ac­ter­is­tics with the trailing edge and the inte­grated radial diffusor. This reduces the deflec­tion and pres­sure losses when the fan is installed in an air condi­tioner (Fig. 3).

Squaring the circle – prac­tical cubic design

They also thought about prac­tical ways to trans­port and install the fans. Sizes 630 and larger feature a stack­able cubic design with clear instal­la­tion bene­fits for the user, safety during trans­port, and less pack­aging waste. They can also be flex­ibly mounted with hori­zontal or vertical motor shaft. The design makes it possible to isolate the fan from its surround­ings with rubber isola­tors in order to ensure even quieter oper­a­tion.

Figure 3: Deflec­tion and pres­sure losses are reduced when the opti­mized fans are installed in air condi­tioners.

An optional guide profile set for simple instal­la­tion of centrifugal modules with support struc­ture and spring elements is still avail­able. There are no grounds to fear flow losses thanks to the special design of the cube struts. Depending on the condi­tions of instal­la­tion, the centrifugal fans are also avail­able with the proven support brackets (Fig. 4).

Measures increased the effi­ciency of the RadiPac fans by more than 13% over that of the previous models.

Wide optimum effi­ciency range

Taken together, all these measures increased the effi­ciency of the RadiPac fans by more than 13  % over that of the previous models. In addi­tion, a wide optimum effi­ciency range with static overall effi­ciency of 68  % enables the fans to work with minimum power consump­tion at prac­ti­cally every oper­ating point. There are also no unpleasant surprises when it comes to noise (Fig. 5).

Figure 4: Sizes 630 and larger feature a cubic design. Depending on the condi­tions of instal­la­tion, the centrifugal fans are also avail­able with the proven support brackets.

The planned oper­ating point for a system may shift due to changes in the duct­work, for example. Another reason to change the orig­inal oper­ating points could be gradual clog­ging of the filters in the AHU equip­ment. Essen­tial for the RadiPac’s wide optimum effi­ciency range is the ideal inter­play of all fan compo­nents. With their high effi­ciency, simple handling and small foot­prints, these medium-pres­sure centrifugal fans excel in many venti­la­tion and air condi­tioning appli­ca­tions.

Power factor correc­tion

Gener­ally speaking one can say that when several EC fans are oper­ated in parallel, active PFC (power factor correc­tion) can protect against unwanted harmonics. PFC converts the pulsed input current of the EC motors into a sinu­soidal current, which is then shifted so that it is in phase with the voltage. This greatly reduces the harmonic content of the power supply, enabling the rele­vant require­ments of EN 61000-3-2 to be satis­fied without design modi­fi­ca­tions. It also mini­mizes the peak input current values and in many appli­ca­tions, users can select a smaller cross-section cable for the fans’ power lines.

Simple commis­sioning with plug & play

Figure 5: The wide optimum effi­ciency range with static overall effi­ciency of up to 68 % enables the fans to work with minimum power consump­tion at prac­ti­cally every oper­ating point and prevents unpleasant noise-related surprises.

Prac­tical expe­ri­ence has repeat­edly shown that in fans, modern EC drives are consid­er­ably more energy-effi­cient than the conven­tional AC drives that are still frequently used in venti­la­tion and air condi­tioning equip­ment. Regu­la­tions such as Germany’s “Energies­parverord­nung” (energy conser­va­tion regu­la­tion, abbre­vi­ated “EnEV”) and the ErP Direc­tive (Energy-related Prod­ucts Direc­tive) have also done their part to increase the popu­larity of EC tech­nology.

Commis­sioning RadiPac fans with Green­Tech EC tech­nology is simple because neither expen­sive fine-tuning nor addi­tional grounding and shielding measures are required since the control elec­tronics and EC motors are perfectly matched. With the smoothly adjustable speed control typical of EC motors, the fan power can also be precisely adjusted to satisfy indi­vidual needs, with commu­ni­ca­tion via the 0-10 V input or MODBUS RTU.

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