Technical Papers

Controlled Drive of Turbo Compressors

Flexible Frequency Converters in Environment-friendly Refrigeration Units

Refrigeration units are essential in server rooms and computing centers amongst others. Without them the sensitive IT systems would overheat. Most of the traditional refrigeration technologies are not particularly environmentally friendly, though. However, this does not apply to the innovative refrigeration unit eChiller® by the young company Efficient Energy: It uses pure water (R718) as refrigerant and consumes up to 80% less power than conventional solutions. Important components of the eChiller are the frequency converters by the Lueneburg based specialist SIEB & MEYER. They ensure a reliable operation of the turbo compressor in the rather unusual operating environment of a water vapor vacuum.

"The eChiller is the world's cleanest and economically most valuable refrigeration unit," Florian Mayer, Manager of Software and Electronics Development at Efficient Energy, points out. "This solution enables our customers to modernize their continuous industrial processes cooling or to improve their computing center profitability." The eChiller is the only refrigeration unit operating in a capacity range of 35 kW which uses water (R718) as a refrigerant. This has many advantages, for example the unit is not affected by current environmental or safety regulations for refrigerants. Thus, financial and maintenance costs are reduced and users are encouraged to make new investments. Thanks to its high power efficiency the eChiller protects the environment: "Anyone who chooses our refrigeration unit benefits from a significantly reduced carbon footprint and contributes to climate protection.“ says Florian Mayer. "This is why the eChiller is future-proof, quite contrary to conventional refrigeration units. In only a few years current refrigeration units won't be able to fulfill the regulatory requirements anymore."

Water as a Refrigerant – A Clean Alternative

The eChiller technology is based on the following principles: direct evaporation, compression, condensation and expansion of water or water vapor in a closed-loop cycle. The requirement-related process takes place in a vacuum at low pressures between 10 and 120 mbar and hence, in a temperature range of approx. 5 °C to 50 °C. Essential components of the refrigeration units are turbo compressors with compressor wheels with a diameter of 15 cm. They operate at up to 90,000 rpm and increase the pressure and temperature level of the water vapor. The turbo compressors are driven by synchronous motors which are powered by frequency converters.

From the beginning, Efficient Energy relied on the frequency converters of the series SD2S by SIEB & MEYER. "They even were installed in the first prototype from 2007,“ remembers Florian Mayer. Back then, the company purchased the necessary turbo compressors in one complete assembly from an external supplier who brought the solutions by SIEB & MEYER into play. Today the production model of the eChiller operates with a turbo compressor developed by Efficient Energy, however, the frequency converters still come from Lueneburg. According to the development manager there is a good reason why, "The used control method ensures an exceptionally low rotor heating. Additionally, the devices could always be adjusted to the changing requirements very well thanks to the flexibly configurable software."


Flexible Configuration and Control

The parameterization of SD2S can be adjusted to, for example, the relatively stable loads of the refrigeration units. "This is a sharp contrast to the extremely dynamic applications that our frequency converters are generally used for,“ explains Ralph Sawallisch, Key Account Manager Drive Electronics at SIEB & MEYER. "That's not a problem, since SD2S has been designed for a wide range of applications from the very beginning." The flexible SD2S software enables the operation of highly dynamic servo motors and high-speed motors in asynchronous and synchronous technologies. Depending on the application, SD2S can operate without a sensor, for example, in case of spindles in machine tools. Naturally, SD2S can also operate with sensors, for example, highly dynamic tightening spindles in the automotive industry. The efficient parameterization software drivemaster2 supports the customer when it comes to customer-specific parameterizing and initial operation.

The SD2S is not only flexibly configurable but can also be directly controlled by an external control device. The connection with the higher-ranking control can be established via various options – interfaces for analog reference value signals (+/-10 V), digital I/Os, RS232 and USB as well as CAN bus are available. Connections to Profibus or EtherCAT are optionally available via a gateway.The integrated control specifies the speed of the frequency converters during operation of the eChiller. This enables the turbo compressor to transport a sufficient volume of water vapor and thus achieve the required performance. Speaking of water vapor: "The turbine of the eChiller is operated in a water vapor vacuum which is an extreme operating environment. Hence, the unit's components have to withstand these extreme conditions,“ explains Ralph Sawallisch. "Such requirements are extremely rare in the industrial field."

In Planning: Individual Adjustment

Currently both companies collaborate to optimize the frequency converter: A water cooling shall enable to operate the eChiller with the next smaller SD2S devices. This would not only mean a cost benefit for Efficient Energy, but also for the end customer. For this purpose SIEB & MEYER adjusts the design of the serial device. If this adjustment proves to be effective, a follow-up project is possible: Efficient Energy would like to implement the frequency converter in the unit in the long run. This means that even more costs would be reduced, as the device would no longer be installed in a separate switch cabinet. "The requirement for this would be a modified design of the SD2S with a new board layout,“ explains Florian Mayer. A challenge that is certainly manageable with SIEB & MEYER as partner. "SIEB & MEYER is well-staffed and employees are able to support individual projects throughout the entire process. This is an additional benefit for our company.“


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