Besides the required air flow, noise emis­sion and energy effi­ciency are key char­ac­ter­is­tics for axial fans used in the evap­o­ra­tors, condensers and heat exchangers in venti­lation, refrig­er­a­tion and air condi­tioning systems. These two char­ac­ter­is­tics are becoming increas­ingly impor­tant for users, due to both legal regu­la­tions such as the ErP (Energy-related Prod­ucts) Direc­tive and higher energy prices and increasing envi­ron­mental aware­ness. This trend will gain in impor­tance in the future. For example, further restric­tions in the ErP Direc­tive are already looming; the next steps are planned for 2020.

Modern axial fans showed impres­sive gains in effi­ciency and quiet­ness in the last few years. Their devel­op­ment has been char­ac­ter­ized by contin­uous improve­ment. For example, while overall static effi­ciency was around 35% in 2004, it increased over the following eight years to approx­i­mately 45% even as noise levels decreased by as much as 7.2 dB(A) compared to previous models. For the motors, there is currently little room left for improve­ment; for example, Green­Tech EC motors with effi­cien­cies well over 90% already consid­er­ably exceed the values known from the IE4 effi­ciency class.

Making the most of poten­tial improve­ments

Figure 1: Losses in a free-blowing axial fan, measured with guard grille.

For further improve­ments, fan manu­fac­turers have to do a lot of “tweaking.” While doing so, they need to consider the fan as a complete system consisting of impeller, motor, housing and control elec­tronics in order to maxi­mize the poten­tial for improve­ment. All compo­nents, and even the circum­stances of instal­la­tion in the user device, have to be consid­ered in the improve­ment process (Fig. 1). Today, effi­ciency increases can only be achieved with improve­ments in aero­dy­namics. Appli­ca­tion-specific oper­ating points have to be taken into account during aero­dy­namic opti­miza­tion to ensure that the fans really do operate at the best possible level of effi­ciency when actu­ally installed.

Now the motor and fan specialist ebm-papst has put this approach to work in devel­oping the new AxiBlade axial fans (Fig. 2). They can work in a wide range of appli­ca­tions with an effi­ciency optimum of up to 54% while reaching a noise reduc­tion of up to 8 dB(A) when compared with the stan­dard program. Besides the espe­cially energy-effi­cient Green­Tech EC motors, the new models are also avail­able with the AC motors that are still widely used. Sizes 800 and 910 are currently avail­able.

The right solu­tion for every pres­sure range

Figure 2: The AxiBlade system with guide vanes.

With fans, different back pres­sures have to be taken into consid­er­a­tion depending on the appli­ca­tion and condi­tions of instal­la­tion. There is no fan that will work with the same effi­ciency or noise level under all condi­tions; any search for an all-purpose unit will be futile. In view of the expected appli­ca­tion condi­tions, opti­mized Plug & Play system solu­tions of the AxiBlade range are avail­able.
Depending on the pres­sure ranges required, the use of guide vanes is recom­mended. The pres­sure-raising effect mini­mizes exhaust turbu­lences, thus the dynamic losses – thus, they contribute to the high energy balance. In addi­tion, there are impellers with special blade geom­etry and winglets for maximum effi­ciency; they are designed for the different motors they can be combined with. This, too, increases effi­ciency and reduces noise.
The user can have Green­Tech EC motors with inte­grated control elec­tronics or conven­tional AC motors installed as drives. And the guard grilles, which are matched to the various combi­na­tions, are also aero­dy­nam­i­cally opti­mized. Not only do they protect against acci­dental contact, they also contribute to the high overall effi­ciency of the axial fans.

Figure 3: AxiBlade oper­ating points for typical appli­ca­tions. The dark areas repre­sent high back pres­sures up to 290 Pa, where the system with guide vanes can make the most of its strengths. The light areas repre­sent low to medium back pres­sures (up to approx. 200 Pa) – the range for the version without guide vanes.

In this fashion, the new axial fans can be opti­mally config­ured for a given appli­ca­tion. For example, the version without guide vanes is suited to low to medium pres­sures up to 200 Pa. In this case, the bene­fits of the guide vanes do not come into play. Even without them, the effi­ciency and oper­ating noise are much better than the current industry stan­dard. The guide vanes become inter­esting for high back pres­sures up to 290 Pa, here the guide vanes are essen­tial to reaching high effi­ciency (Fig. 3).

Same foot­print as industry stan­dard

Since the new axial fan’s foot­print corre­sponds to the current industry stan­dard, virtu­ally no design changes in the end unit are neces­sary (Fig. 4). And the fans are lower than the usual models. The height is likely to play a minor role for most appli­ca­tions, but not for trans­port. Every centimeter counts when the fans have to be loaded onto pallets or into containers.

Figure 4: Same instal­la­tion area: More cooling perfor­mance with the same foot­print as previous fans. Pictured here is a condenser for refrig­er­a­tion with ten axial fans.

The bene­fits of the EC versions of the fans are obvious. They include speed control via the inte­grated elec­tronics, enabling the speed to always be adjusted to match the current require­ments. This pays off quickly for the user since EC motors also excel with their high effi­ciency in partial-load oper­a­tion and are extremely quiet compared to speed-controlled asyn­chro­nous motors, whose triac or vari­able frequency drive control systems inevitably generate noise. Further bene­fits include high power density, compact size and constant moni­toring of oper­a­tional data and status infor­ma­tion.

The latest EC motor, which is also used in the new modular system, also features program­mable inter­faces and can be used around the world since it works with all voltage vari­ants and power systems. Wire­less config­u­ra­tion is possible using RFID (radio frequency iden­ti­fi­ca­tion) and a status LED shows the oper­ating modes. All in all, AxiBlade fans for evap­o­ra­tors, condensers and heat exchangers and precon­fig­ured to user require­ments in the factory, are ideal for satis­fying the increas­ingly exacting require­ments for energy effi­ciency, quiet­ness, low oper­ating costs and conve­nience, today and in the future.