Diag­onal fans make filter fans more effi­cient

Filter fans are a combi­na­tion of fan and dust filter. They are well suited for econom­i­cally dissi­pating heat loads from switch cabi­nets or elec­tronics enclo­sures. A new gener­a­tion of equip­ment is now providing a breath of fresh air – in more ways than one – in the field of housing and control cabinet tech­nology: with a flat design, good pres­sure stability, constant perfor­mance and reduced noise char­ac­ter­is­tics. More­over, tool-free (and there­fore time-saving) instal­la­tion makes it conve­nient for the user. Diag­onal fans which can be perfectly inte­grated into the appli­ca­tion make an essen­tial contri­bu­tion here. These combine the char­ac­ter­is­tics of conven­tional axial fans with those of centrifugal fans.

To ensure that elec­tronics work reli­ably, the residual heat gener­ated from the power loss has to be dissi­pated as effi­ciently as possibly. In prac­tical use, it soon becomes clear that there are often great differ­ences in the perfor­mance of the filter fans used for this purpose. The strengths and weak­nesses of the different fan concepts are partic­u­larly evident when there is a high back-pres­sure, e.g. due to a high density of compo­nents or dirt accu­mu­la­tion in the filter mats.

More pres­sure and higher air flow

New line of diag­onal fans for filter fans from ebm-papst

Usually, filter fans employ axial fans, in which the air flows parallel to the axis of rota­tion of the impeller. These fans displace large volumes of air, but with low static pres­sure. Outside the right working range, i.e. with increasing pres­sure rise beyond the saddle point, the noise level of axial fans rises substan­tially as the air flow at the impeller shears and forms turbu­lence. This causes the effi­ciency of the fan to drop. For this reason, centrifugal fans are usually the right choice for appli­ca­tions requiring greater pres­sure stability. Here, the air flows across the impeller radi­ally to the axis of rota­tion. Because the complete air flow leaves the impeller at the outer diam­eter, the greater speed encoun­tered there is fed into energy, meaning that the centrifugal impeller is able to generate a greater pres­sure increase. Motor and fan specialist ebm-papst has married the bene­fits of these two fan concepts in a new line of diag­onal fans. The filter fans, which are config­ured for an air perfor­mance ranging from 20 to 900 cubic metres per hour, are flatter than earlier models featuring axial fans, yet they have the same instal­la­tion dimen­sions and generate a greater air flow at higher back-pres­sure, with better noise char­ac­ter­is­tics and lower power input. This new gener­a­tion of fans has been specially devel­oped by ebm-papst for the Rittal TopTherm line of filter fans.

Longer service inter­vals and substan­tial energy savings

The char­ac­ter­is­tics curve for the diag­onal fan shows a substan­tially higher pres­sure increase compared to axial fans. And yet the power input is lower despite the higher air volume.

The key to this is the so-called diag­onal fan employed in the new gener­a­tion of filter fans. These fans are supplied by ebm-papst and occupy a posi­tion between the two fan lines described above. The prin­ciple here is for the fan blades to push both axially and centrifu­gally with an axial inflow. The advan­tage of such a config­u­ra­tion is that the air flow largely corre­sponds to that of the regular axial fan but with a greater pres­sure build-up. The char­ac­ter­istic curve is steeper and the saddle is higher. When installed under oper­ating condi­tions, the air perfor­mance is more constant over a wide range, which means a number of advan­tages in prac­tice.

The filter fans avail­able for an air perfor­mance of 20 to 900 cubic metres per hour are flatter than the earlier versions with axial fans with other­wise unchanged instal­la­tion dimen­sions and substan­tially greater pres­sure stability.

The power loss when the filter mats are cont­a­m­i­nated is substan­tially lower. This means longer service inter­vals, which natu­rally reduces costs for the user. If the fan is controlled by a ther­mo­stat, the volume flow reserve will cause the power input and the time for which the fan can run in its optimum power range to be reduced. Exten­sive tests have shown that energy savings of up to 40% can be achieved with an unchanged air volume. Further savings poten­tial is achieved if modern EC motors are employed in the fans. These work with great effi­ciency and are able to adjust their speed in accor­dance with the actual cooling require­ments. This is imple­mented with a special controller from Argus Vision, which partially senses the temper­a­ture at a hot spot inside the switch cabinet to control the fan’s air volume according to require­ments. Because such energy-saving fans have the same dimen­sions as the AC versions of the diag­onal fan, a subse­quent conver­sion is possible without any prob­lems.

Even air distri­b­u­tion and quiet running

The outlet direc­tion on diag­onal fans is not axial to the fan but rather diag­o­nally outwards, which provides for an even air distri­b­u­tion in the switch cabinet or housing. This effec­tively prevents heat pockets from forming. In addi­tion, the fans run extremely quietly. This is due firstly to the way in which they work, and secondly to the fan impellers and hous­ings, which have been opti­mised according to aero­dy­namic criteria and the plastic mate­rial used. In contrast to the sheet metal construc­tions other­wise employed, plastic parts are rela­tively easy to shape. While sheet metal parts can only be bent and stamped, plas­tics can easily be shaped into three-dimen­sional profiles. The plastic mate­rials used are light, yet durable, UL-approved, flame-resis­tant and noise-insu­lating. With the new filter fans, the noise level is reduced by up to 10 dB(A) compared to earlier versions with the same air volume.

High flex­i­bility in assembly

Many different details have been incor­po­rated into the mechan­ical, patent-protected design of the diag­onal fans. Their hous­ings consist in prin­ciple of two multi­func­tional shells. In one half of the housing are the inlet vents, guard grille and spacers for the filter mat. In the other half is the rear guard grille and the motor support. Between the two parts is the connector terminal with inte­grated wire ducting. The fan and the filter housing can be joined in four different posi­tions thanks to the bayonet coupling. This allows cable outlet posi­tions every 90°. No extra tool is needed for this. The same thing applies to changes in the direc­tion of air flow. Here, all the user has to do is to release the bayonet coupling on the diag­onal fan, turn the fan unit through 180° and lock into place again.

Mechan­ical details on the fan housing make assembly easier.

This inte­grated system solu­tion was devel­oped in the space of one year, from the start of the project to the first parts being ready for series produc­tion. An essen­tial precon­di­tion for this short real­i­sa­tion time was the use of modern simu­la­tion tools such as CFD compu­ta­tion of the aero­dy­nam­i­cally rele­vant compo­nents, FEM analysis of the load-bearing housing compo­nents and filling and warpage simu­la­tion of the plastic parts. But besides tech­nical work, it was above all the outstanding and honest coop­er­a­tion between customer and supplier that formed the basis for the success of the project.