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EC centrifugal fans for fan filter units

Neat energy-saving solu­tions for clean-room appli­ca­tions

Tougher product quality require­ments call for produc­tion in clean or ultra-clean rooms. Even the smallest of impu­ri­ties in the air can adversely affect produc­tion processes and lead to high scrap rates. The air supply in such produc­tion envi­ron­ments needs to be almost 100% free of dust and germs, and fans play an impor­tant role in this. However, they should be capable of more than simply “moving air”. Besides the required air perfor­mance, compact dimen­sions, low noise emis­sion, mate­rials suit­able for clean room use, appro­priate controls, networking capa­bil­i­ties and energy-effi­cient 24/7 oper­a­tion are among the crucial criteria.

Clean-room condi­tions are manda­tory for many of today’s produc­tion processes, not only in the semi­con­ductor industry. Exam­ples include optics and lasers, aero­space, biosciences, medical research and treat­ment, the produc­tion of food­stuffs and phar­ma­ceu­ti­cals, and nanotech­nology. Clean-room tech­nology prevents cont­a­m­i­na­tion from compro­mising produc­tion processes and damaging the sensi­tive prod­ucts (product protec­tion). In addi­tion, some produc­tion processes involve substances that may not be released into the outside air. Here, too, clean-room tech­nology is neces­sary to prevent toxic or other reac­tive substances from leaving the protected area and endan­gering the envi­ron­ment or human health (personal safety).

Energy-saving clean-room oper­a­tion


Figure 1: Clean-room venti­la­tion: There are two flow systems, turbu­lent (left) and laminar (right)

Clean rooms impose special require­ments on their venti­la­tion systems (Fig. 1), including suffi­cient air throughput and pres­sure, exact regu­la­tion of temper­a­ture and humidity, and consis­tent air quality. This applies regard­less of the air circu­la­tion method (Fig. 2) or the room size. These require­ments can be met by so-called fan filter units (FFU), which combine filter systems and fans and are designed for ceiling instal­la­tion, partic­u­larly in large clean rooms (Fig. 3).


Figure 2: Plug fan module, ready for connec­tion, for fan filter units (FFU, left), clean room ceiling FFU with filter for airborne parti­cles on the bottom (right)

The oper­a­tion of clean rooms with FFUs is the most econom­ical means of supplying extremely clean air. At the core of these FFUs are extremely compact, modular built-in fans with a very flat design that need little space for instal­la­tion. Energy effi­ciency is becoming an increas­ingly impor­tant issue as air condi­tioning and venti­la­tion consume by far the most energy in clean-room oper­a­tion due to their high air exchange rates. Energy costs and effi­ciency were once matters of secondary impor­tance, but this point of view is now being recon­sid­ered.
Rising energy prices and the public interest in lowering green­house gas emis­sions have prompted all leading compa­nies to focus on energy effi­ciency. Currently, FFU manu­fac­turers have to guar­antee overall effi­ciency of at least 50% in clean-room appli­ca­tions. Not only are fans with a highly compact design called for, they also have to work effi­ciently. This makes Green­Tech EC tech­nology espe­cially inter­esting for use in clean rooms, since FFUs equipped with it achieve effi­cien­cies of more than 50%, impos­sible with conven­tional fan tech­nology. Green­Tech EC fans can also meet strict require­ments in terms of noise emis­sion. In partic­ular, RadiCal® fans are 6-7 dB(A) quieter than the previous market stan­dard, a consid­er­able improve­ment in both clean-room noise levels and worker comfort.


Figure 3: Compact fans with energy-effi­cient Green­Tech EC tech­nology for use in fan filter units

Motor and fan specialist ebm-papst Mulfingen offers a range of EC centrifugal fans specially designed for use in fan filter units and meeting all manda­tory require­ments for this appli­ca­tion (Fig. 4). They are avail­able in diam­e­ters of 310, 355 and 400 mm with air perfor­mance of 1170, 1750, and 2330 m³/h at a back pres­sure of up to 250-300 Pa. These fans are very compact thanks to their external rotor design, and with heights from 190 to 275 mm, they are also rela­tively flat, so they can be easily inte­grated in the equally compact FFUs.

Easy control and networking

Thanks to their high effi­ciency, EC motors also generate little waste heat released into the circu­lated air, so the produc­tion envi­ron­ment is subject to less thermal stress, which reduces the demand on the cooling systems consid­er­ably. The speed of fans with EC tech­nology can also be controlled smoothly and easily, so their air perfor­mance can always be adjusted to current needs. In terms of economy, this also makes sense as EC motors have a signif­i­cantly higher effi­ciency in partial-load oper­a­tion than motors based on other control concepts. After all, over­sized air volumes will not neces­sarily lead to better product quality, but will inevitably result in unnec­es­sarily high oper­ating expenses. The right setting for the appli­ca­tion is crucial.

For demand-based oper­a­tion, the EC fans can be controlled via an analogue 0-10 V signal or a digital RS-485 inter­face. The latter lends itself best to clean-room use, where several thou­sand fans are often in service in the FFUs. In such cases, the networking capa­bil­i­ties with Modbus or ebmBUS have proven very effec­tive in prac­tice. From config­u­ra­tion during commis­sioning to service, fault diag­nosis and main­te­nance, making tech­nical adjust­ments is consid­er­ably easier if the fans can be accessed from a central PC. The drives can be tied into the higher-level building manage­ment control system via the bus inter­face. The motor speeds can be smoothly adjusted via this inter­face, which provides a very conve­nient means of adjusting perfor­mance to meet demand.


Figure 4: The intu­itive EC-Control soft­ware for EC fans networked via Modbus and ebmBUS

The air perfor­mance of the FFUs can be perfectly matched to the clean room’s ambient and oper­ating condi­tions. If a fan in the filter ceiling fails, it can be compen­sated for by increasing the speeds of the neigh­bouring FFUs. Such a strategy for dealing with fail­ures provides a high degree of oper­a­tional reli­a­bility by main­taining the correct air flow. From config­u­ra­tion and program­ming to alarm manage­ment, ebm-papst’s FFU control soft­ware (Fig. 5), which is suit­able for use with Modbus and ebmBUS, simpli­fies systems engi­neering tasks.

During oper­a­tion, the user also bene­fits from other features of EC tech­nology. The fans are very quiet; their drives have fault­less noise prop­er­ties throughout their speed range so they can meet the strin­gent noise suppres­sion require­ments applying to produc­tion in clean rooms. This low noise emis­sion is mainly due to the aero­dy­nam­i­cally opti­mised centrifugal impellers.

Metal or plastic centrifugal fans

When­ever fans are used in clean rooms, their impellers are usually made of metal. There are always reser­va­tions when it comes to using plas­tics in the venti­la­tion systems of clean rooms. The addi­tives needed in plas­tics produc­tion are suspected of outgassing and endan­gering clean-room processes. The situ­a­tion is completely different for appli­ca­tions where cont­a­m­i­na­tion by metals must be ruled out, such as wafer produc­tion. Here, fans made of plastic are clearly a blessing. To rule out risks to clean-room produc­tion that are asso­ci­ated with plastic parti­cles in the circu­lated air, ebm-papst  care­fully analysed the issue of outgassing.


Figure 5: The RadiCal® fan line is espe­cially suit­able for use in fan filter units

The RadiCal® range of fans has been rigor­ously tested for substances prohib­ited in clean-room oper­a­tion; these substances have been eval­u­ated as per the semi­con­ductor industry’s ITRS stan­dard. RadiCal® impellers from ebm-papst passed the rele­vant tests with flying colours. According to the test results, the plas­tics used are non-hazardous. The emis­sion level of poten­tial cont­a­m­i­nants is well below the permitted limits. In clean-room appli­ca­tions, too, users can now enjoy the full benefit of the inno­v­a­tive design of these plastic impellers. After all, plastic offers a consid­er­ably greater range of design options than sheet metals. The overall design of the fan results in an improved air flow through the impeller, signif­i­cantly increasing the fan’s aero­dy­namic effi­ciency. The rounded inlet contours on both the cover plates and the base plates of the impellers play a part in this, too. More­over, the inter­ac­tion between the inlet nozzle and the impeller inlet has been improved signif­i­cantly.

These EC fans, in combi­na­tion with the aero­dy­nam­i­cally opti­mised plastic impellers or the proven aluminium blades, are energy-effi­cient, compact and adjustable compo­nents for fan filter units, well suited to the require­ments of clean-room appli­ca­tions in every respect. Their perfor­mance has been proven around the world, including clean rooms in which flat screens are produced. For good reason, the market leaders from Korea and Taiwan chose Green­Tech EC tech­nology from ebm-papst for the produc­tion of their big flat-screen prod­ucts.

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Filter-fan-units in cleanrooms

More than just moving air