Oper­ating clean­rooms with FFUs is the most econom­ical option to ensure a clean air supply. At the core of these FFUs are compact, modular, built-in fans that are as flat as possible, meaning that they require little instal­la­tion space, and work with high energy effi­ciency. However, inte­grating the systems into a network is also becoming increas­ingly impor­tant. The air supply in a clean­room is not usually a stand­alone solu­tion. Instead, it is inte­grated into the entire automa­tion process and its PLC and SCADA systems. Just like all other sensor and actu­ator infor­ma­tion, the fans of the FFUs have to be inte­grated into the system network, and their status infor­ma­tion must be provided to the controls and visu­al­iza­tion systems.

Figure 2: Fans with a MODBUS daisy-chain inter­face (DCI) can be addressed auto­mat­i­cally by the master via a hard­ware signal. This makes commis­sioning proceed much more quickly. (Photo | ebm-papst)

The initial commis­sioning of a clean­room system requires a signif­i­cant output of time and money. Based on user reports, the time required to manu­ally connect an FFU data point is around five to ten minutes. The more fans there are in use, the more poten­tial there is to make savings. The fan and motor specialist ebm-papst has responded to this and offers EC centrifugal fans, which are specially designed for instal­la­tion in FFUs and have a digital MODBUS RTU inter­face, with auto­matic addressing, which can signif­i­cantly reduce commis­sioning costs (Fig. 2).

MODBUS RTU with auto­matic addressing

A master/slave-based bus always requires unique slave addresses. The fans are usually deliv­ered with an address that is preset in the factory, which is always the same (e.g. slave ID = 1). There­fore, the addresses must be assigned a unique address during commis­sioning for oper­a­tion in the network group, prefer­ably in the order of the MODBUS cabling. This time-inten­sive process is now auto­mated using “DCI” (daisy-chain inter­face) addressing.

The master controller is able to manage the complete addressing proce­dure along with the local­iza­tion of the FFU devices.

A fan equipped with a DCI is addressed by a hard­ware signal (15 V/24 VDC) via the Init pin on the RJ45 network plug, and thus temporarily becomes slave address 247. Only the unit acti­vated in this manner “listens” to messages sent to this DCI address 247, and accepts a new MODBUS address sent by the master controller to this slave. Following successful re-addressing of this fan, its DCI relay is switched on and the hard­ware signal (15 V / 24 VDC) is switched on to the Init pin of the next fan module in the chain. This fan is now acti­vated via the hard­ware signal (Init pin) and the addressing continues as described above.

If the cable diagram is known, the posi­tion of the fan unit in the clean­room ceiling can be deter­mined using the order of the addresses or the cable route. The instal­la­tion loca­tion can be iden­ti­fied using the order in which the addresses are allo­cated. Manual assign­ment is no longer neces­sary; the master controller is able to manage the complete addressing proce­dure along with the local­iza­tion of the FFU devices which are installed in the clean­room ceiling. There is a signif­i­cant reduc­tion in the time and costs for commis­sioning.

Energy-effi­cient and quiet

Figure 3: The fans from the RadiCal product range are partic­u­larly well-suited for use in filter-fan-units. (Photo | ebm-papst)

Once put into oper­a­tion, the energy effi­ciency of the fans becomes an impor­tant matter. Nowa­days, FFU manu­fac­turers have to guar­antee overall effi­ciency levels of at least 50% in clean­room appli­ca­tions at the design point. There­fore, there is a great demand not only for fans that are as flat as possible, but also for fans that work energy-effi­ciently. EC tech­nology there­fore has a lot to offer clean­room tech­nology, as FFUs equipped with it can achieve effi­ciency levels of well over 50%. EC fans can also be used to meet strict noise emis­sion require­ments.

RadiCal centrifugal fans lend them­selves partic­u­larly well for this purpose (Fig. 3), as their impellers have been opti­mized according to aero­dy­namic criteria. They there­fore contribute to a signif­i­cant noise reduc­tion of up to 7 dB(A) compared to the conven­tional industry stan­dard, which human hearing perceives as half as loud. The quiet and energy-saving fans are avail­able with diam­e­ters of 250, 310, 355, and 400 mm, and cover air perfor­mance levels in the ranges of 580, 1,170, 1,750, and 2,330 m³/h, with a back pres­sure of up to 250 to 300 Pa. Thanks to their external rotor design, they are very compact and above all extremely flat, at a height of 190 to 275 mm, meaning that they can be easily inte­grated into the equally compact FFUs.

Impellers made of plastic composite mate­rials have already been success­fully intro­duced for use in many clean­room envi­ron­ments, and have proven effec­tive. Never­the­less, ebm-papst has had the rele­vant mate­rials tested for clean­room compat­i­bility in an external labo­ra­tory. The fans in the RadiCal product range were exam­ined thor­oughly for substances that are prohib­ited in clean­room oper­a­tion, and eval­u­ated according to the stan­dards of the semi­con­ductor industry. They passed the corre­sponding tests with flying colors, as the mate­rials used are harm­less, as is the outgassing process. This means that in clean­room tech­nology too, users can benefit from the energy-saving, inno­v­a­tive design of the plastic impellers. After all, plastic offers a much wider range of design options compared to sheet metal mate­rials. As a result, the design of the whole fan leads to improved air flow through the impeller, which signif­i­cantly increases aero­dy­namic effi­ciency.

Figure 4: The EC fans can be easily inte­grated into the FFU. They are supplied as ready-to-connect systems, which have been tested at the factory. (Photo | ebm-papst)

Wide voltage input with active PFC

The EC fans can easily be inte­grated into the FFUs (Fig. 4). They are supplied as ready-to-connect systems that have been tested at the factory, either as EC centrifugal fans with a cable and connector panel, or as fully assem­bled fan instal­la­tion modules complete with nozzle plate, motor support plate, profile struts, and guard grill. Thanks to a wide voltage input, they are suit­able for inter­na­tional use with a wide variety of line volt­ages and line frequen­cies. The stan­dard active PFC (Power Factor Correc­tion) prevents the permis­sible harmonic limit values from being exceeded during the parallel oper­a­tion of many EC fans, which would other­wise put a strain on the supply network.

Thanks to a wide voltage input, the EC fans are suit­able for inter­na­tional use.

All energy distri­b­u­tion compo­nents such as network trans­formers, fuses, switches, and cable cross-sections can be designed to be much smaller and more cost-effec­tive due to the active PFC. Addi­tional external harmonic filters are not required. But it is not only in large clean­rooms where users are well-served by EC centrifugal fans. ebm-papst also offers suit­able compo­nents and system tech­nology for FFU oper­a­tion and moni­toring for smaller clean­room cabins.