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Bitzer screws in novel data cooling project

GERMANY: Italian manufacturer HiRef SpA is using Bitzer screw compressors to cool a computing centre adiabatically with air-to-air heat exchangers. 

HiRef SpA, a specialist in air conditioning systems for data centre and telecoms, had the task of designing a cooling system in cooperation with Cooltec Systems Kälte Klima GmbH for a computing centre in the German city of Offenbach. 

A long-term customer of Bitzer, HiRef saw a sustainable refrigerant being of key importance, along with high efficiency at full and part load. HiRef opted for an unusual solution. For the first time, 96 screw compressors with external frequency inverters were installed in the 48 cooling systems instead of scroll compressors. These use R513A but can be converted to use the low GWP HFO refrigerant R1234ze at a later date.

As one of the first HiRef systems with the adiabatic system, this project was of special significance. “We wanted there to be no doubt that the quality of our environmentally friendly and sustainable solution surpasses everyone else in the market – that is another reason why we used screw compressors instead of scrolls,” explained HiRef commercial director Wolfgang Fels. 

With screw compressors, certain temperature levels can be maintained precisely and constantly. If the preset maximum temperature set point is exceeded, the evaporative cooling system lowers the condensing temperature and therefore the energy intake. Speed-controlled by frequency inverters, the screw compressors provide full mechanical backup for the cooling capacity. 

“Capacity control makes the screw compressors extremely energy efficient at full and part load,” Fels added.

Every system has a cooling capacity of 200kW and is fitted with EC fans and a special high-efficiency crossflow heat exchanger with a corrosion resistant epoxy coating. The double-ended parallel electrical feed has a quick-start feature as well as uninterrupted control of the power supply. 

The cooling process is based on three different principles: full free cooling with a winter bypass, needs-based, modulating, mechanical cooling with maximised free cooling, and modulated, mechanical cooling with an adiabatic spray system in the condenser.

The integrated oil separator in the Bitzer CSH65 screw compressors and the built-in suction-gas-cooled motor simplify system integration and, according to Bitzer, allow for a compact, cost-efficient system design. 

Besides lower life cycle costs and 24/7 reliability under any operating conditions, sound insulation was of critical importance in this project. The compressors’ special enclosure ensures maximum sound insulation, while the integrated pulsation mufflers reduce sound on the exhaust air side.

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