Air purifi­ca­tion units gener­ally make use of a multi­stage filtering and sepa­ra­tion process. Fans ensure that the cont­a­m­i­nated air extracted from metal­working machines passes through the various filter systems (Fig. 2), safely extracting emis­sions such as oil and emul­sion mist and suspended partic­u­late matter. This process calls for fans that generate rela­tively high pres­sure from a low air flow.

Figure 1: Modern CNC cutting machines increase the amount of cont­a­m­i­nants in the air in factory build­ings; this can be reme­died by air puri­fiers. (Photo | ISI-Indus­triepro­dukte GmbH)

The high pres­sure is needed to over­come the resis­tance from the filters. The fans should also be as easy to control as possible. The extrac­tion flow can then be adjusted to the actual need, enabling energy-saving partial-load oper­a­tion that also extends the service life of the filters. At the same time, the extrac­tion perfor­mance can be kept constant in spite of increas­ingly clogged filters by appro­pri­ately adjusting the motor speed, and perfor­mance reserves can be made avail­able for future system expan­sion as the speed and air perfor­mance can be adjusted as needed later.

AC motors reach their limits

Figure 2: Fans ensure that the cont­a­m­i­nated air extracted from metal­working machines passes through the various filter systems. (Photo | ISI-Indus­triepro­dukte GmbH)

Until recently, AC motors with vari­able frequency drives had been consid­ered suit­able for oper­ating fans. That has changed, since such motors often fail to comply with the current require­ments of the Euro­pean Union’s Ecode­sign (ErP) Direc­tive. Now modern EC fans often present an ErP-compliant alter­na­tive in many cases (Fig. 3). An example is the inno­v­a­tive Green­Tech EC tech­nology devel­oped by ebm-papst, which can play out all its strengths in air puri­fiers. EC motors are basi­cally perma­nent-magnet synchro­nous motors in which a magnetic rotor synchro­nously follows an elec­tron­i­cally gener­ated rotating field. Their control elec­tronics allow oper­a­tion at any speed, even above the 3,000 rpm limit imposed on asyn­chro­nous motors by the line frequency.

High effi­ciency, smooth oper­a­tion and connec­tivity

EC fans work at much higher effi­ciency levels than asyn­chro­nous motors. Their opti­mized commu­ta­tion allows partial-load oper­a­tion down to 1:10 without a loss of effi­ciency, while their air flow can be adjusted as needed with a 0-10 V linear or PWM input. A PID controller is inte­grated in their motor elec­tronics. Multiple fans can be conve­niently networked via MODBUS and then controlled with a centrally connected air-moni­toring system, and of course diag­nostic and warning func­tions can also be used via the bus at the same time.

Figure 3: EC motors from ebm-papst signif­i­cantly exceed the effi­ciency level called for by the ErP Direc­tive.

The high effi­ciency of the EC motors not only saves energy and lowers oper­ating costs, but also gener­ates less waste heat so that factory build­ings are not addi­tion­ally heated by the air puri­fiers during the summer. Commu­ta­tion and the motor design also ensure very smooth oper­a­tion.

Figure 4: “Sifted air”: Air-inlet guards reduce noise by straight­ening out the air flow.

The high cycle frequen­cies are acousti­cally imper­cep­tible, reducing noise emis­sions and making these “stealth fans” ideal for appli­ca­tions in which noise protec­tion regu­la­tions must be observed; in some cases, manu­fac­turers can then use less insu­la­tion.

But it is also possible to go a step further. Moving air is always accom­pa­nied by a certain amount of noise. If the EC fans are now combined with air-inlet guards (Fig. 4) on the intake side, a drastic reduc­tion in noise emis­sion results and turbu­lence and annoying low-frequency sounds are mini­mized. This reduces the fric­tions that can other­wise arise when people and machines share the same space.

Easy instal­la­tion and commis­sioning

The fans from ebm-papst with back­ward-curved, aero­dy­nam­i­cally opti­mized aluminum impellers for use in air puri­fiers are avail­able in sizes 250 and 310 (Fig. 5). They cover a range of drive powers between 250 watts and 12 kW.

Figure 5: Compact and easy to install: EC fans for emis­sions extrac­tion.

Flex­ible options for instal­la­tion include short delivery times and mounting with vertical or hori­zontal motor shaft orien­ta­tion. With their compact dimen­sions, they are also suit­able for retro­fits, as when energy-saving replace­ments are called for or increased air perfor­mance is needed in a limited space. Such retro­fits usually require minimal adap­ta­tions, if any.

Since the elec­tronics and motors in the EC fans are combined in a single unit, instal­la­tion is simpli­fied and requires less space. Since the motor and the elec­tronics in the motor system are already perfectly matched, there is no need for addi­tional elec­tronic filters and shielded cables. Nor is an external motor protec­tion switch required.

Costly adap­ta­tions during commis­sioning in the air purifi­ca­tion units can be dispensed with, as can grounding and shielding. All these char­ac­ter­is­tics make the energy-effi­cient and ErP-compliant EC fans a worth­while alter­na­tive for central­ized or decen­tral­ized air purifi­ca­tion units.