One of the most impor­tant tasks of any data center oper­ator is to monitor and control climatic condi­tions in server rooms, as high temper­a­tures and humidity damage the IT devices and result in fail­ures. Air condi­tioning concepts have to coun­teract this. Different solu­tions are used here, as no two data centers are the same in terms of the way they are constructed (Fig. 1).

Typical cooling appli­ca­tions range from in-row cooling of the server racks to chillers, preci­sion air-condi­tioning units and other air handling units (AHUs). ebm-papst has a number of suit­able EC axial and centrifugal fans designed to meet the require­ments in data centers for these different air-condi­tioning solu­tions.

A real-life example: NTT Global Data Center

NTT Global Data Centers EMEA GmbH is one of the world’s leading IT service providers with four data center loca­tions in Frank­furt alone. The Frank­furt 1 data center campus, for example, is one of the largest data center sites in Europe, with around 50,000 square meters of IT space (Fig. 6) featuring preci­sion air-condi­tioning units providing cooling. The units draw in exhaust air at a temper­a­ture of around 36 to 39°C, filter, cool, and humidify it, then direct the air, which has been cooled to 23 to 24°C, through a raised floor and outlets directly to the server racks. Three EC centrifugal fans from the ebm-papst RadiPac series are respon­sible for contin­u­ously conveying air in each air condi­tioner

In total, these fans have been in oper­a­tion in Frank­furt 1 for almost 10 years. There is one special thing to note here, though: the standby preci­sion air-condi­tioning units are not only provided for redun­dancy reasons, they also always run at low speed in parallel. This increases both the service life of the fans and their effi­ciency.

Thanks to precise differ­en­tial pres­sure control in the range of four to six pascals, the fan speed of all air condi­tioners auto­mat­i­cally adjusts when a preci­sion air-condi­tioning unit fails or if the server perfor­mance changes dynam­i­cally. As a result, all the fans consume an impres­sive 30 percent less power, thereby playing their role in ensuring a good EER value, which indi­cates the cooling capacity of an air condi­tioner compared to the current consump­tion.

Axial fans: quiet and suit­able for high back pres­sure

Data centers are increas­ingly moving closer to both indus­trial and resi­den­tial areas in order to keep data cables short and there­fore as inter­fer­ence-free as possible. This has conse­quences for the oper­a­tors, as the large chillers, dry coolers, or condensers have to comply with the applic­able noise protec­tion regu­la­tions in the rele­vant area. For the fans used, this means two things. Firstly, they them­selves must operate as quietly as possible and not cause any unpleasant noise. And secondly, they must also cope with higher back pres­sure if the air condi­tioners require addi­tional noise protec­tion measures, for example because the compressor would other­wise be too loud.

AxiBlade and AxiEco are two axial fan series that cover the different require­ments here (Fig. 2). The first boasts a high power density with low noise emis­sions, while the second series is partic­u­larly suit­able for appli­ca­tions requiring an espe­cially high pres­sure increase, for example due to addi­tional noise protec­tion measures or special exchanger geome­tries.

Centrifugal fans: high power density and wide optimum effi­ciency range

Centrifugal fans are also typi­cally used in data centers. During the devel­op­ment of RadiPac centrifugal fans, for example, the actual instal­la­tion situ­a­tion in computer room air handlers (CRAH) and AHUs was taken into account. Specif­i­cally, the outflow char­ac­ter­is­tics of the impeller were opti­mized and both deflec­tion losses in the air handling unit and outlet losses were reduced thanks to a special design. As a result, the fans can run at a lower speed at the same oper­ating point, which in turn enables energy savings (Fig. 3). Thanks to a wide optimum effi­ciency range and a high static overall effi­ciency level, the fans operate with low power consump­tion in a broad range of oper­ating condi­tions.

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Increased oper­a­tional reli­a­bility thanks to reso­nance detec­tion

Fans are used in a wide range of appli­ca­tions in data centers. Depending on the instal­la­tion situ­a­tion, reso­nance can occur in unpre­dictable speed ranges. If the fan is often oper­ated in such crit­ical ranges, the bearing system may be damaged, leading to prema­ture fan failure. Although these vibra­tions can be measured by system oper­a­tors, they cannot simply be elim­i­nated. ebm-papst solves this problem with auto­matic reso­nance detec­tion, which prevents fans from oper­ating at crit­ical speeds, increasing their service life and oper­a­tional reli­a­bility.

For this purpose, a test start-up can be performed during commis­sioning in which the vibra­tion speed is analyzed over the entire speed progres­sion from stand­still to nominal speed. If exces­sive vibra­tion speeds are detected in certain ranges, the control soft­ware adjusts itself after acti­va­tion by the customer so that these speed ranges are “passed over” in the future. This means that the ranges are passed through, but contin­uous oper­a­tion in them is avoided (Fig. 4).

Oper­a­tors can manu­ally edit the soft­ware settings at any time, meaning that they always have full control. The inte­grated vibra­tion sensor can also be used for condi­tion moni­toring, which enables preven­tive main­te­nance and service assign­ments to be better planned.

Active “Power Factor Correc­tion” mini­mizes circuit feed­back

Speed control is manda­tory for demand-based air condi­tioning. However, the oper­a­tion of speed-controlled drives always gener­ates current harmonics, which can become prob­lem­atic in crit­ical infra­struc­tures when combined with an inad­e­quately dimen­sioned power supply. The resulting harmonics lead to an increased load on the supply network and to losses due to reac­tive power. There may also be a nega­tive impact on other devices in the system network. In the past this used to mean that oper­a­tors had to fit external filters, ensure adequate power factor correc­tion, and possibly make use of larger cable cross-sections.

These kinds of external measures are now no longer required. To mini­mize the problem of harmonics with the parallel oper­a­tion of EC fans, ebm-papst has come up with a solu­tion where the harmonic filter is already inte­grated: namely, active PFC (Power Factor Correc­tion (fig. 5)).

The approach is to prevent current harmonics from occur­ring at all instead of labo­ri­ously filtering them out after­wards with addi­tional compo­nents. This allows infra­struc­ture compo­nents for energy and emer­gency power supply, such as trans­formers and emer­gency power gener­a­tors, to be designed to be smaller, making them more cost-effec­tive. The results that can be achieved with active PFC are remark­able: with a power factor of over 0.99, the THD(I) is typi­cally approx. 2% at rated output, and remains below 5% all the way down to 10% of the rated output. THD(I) stands for Total Harmonic Distor­tion of Current.

Equipped for natural refrig­er­ants

The use of natural and flam­mable refrig­er­ants is another issue that data center oper­a­tors have to deal with and the fans described can also be equipped for this purpose. Their elec­tronics circuits would then be designed to comply with EN 60335-2-40 for air condi­tioners with flam­mable refrig­er­ants, i.e. the maximum surface temper­a­ture in the event of a fault must be at least 100 kelvins below the igni­tion temper­a­ture of the refrig­erant used. Propane, which is very well suited to many appli­ca­tions due to its good heat transfer capacity and its low GWP value, has an igni­tion temper­a­ture of 470°C. The elec­tronic assem­blies, which have been tested and certi­fied accord­ingly, ensure that their maximum surface temper­a­ture always remains below 370°C, even if a fault occurs, and as a result they do not become an igni­tion source.