HiRef uses Bitzer's screw compressors to cool a computing centre adiabatically

Date: 14 June 2022

The Italian company HiRef S.p.A. has started to use screw compressors from BITZER to cool a computing centre adiabatically with air-to-air heat exchangers. As the application is fitted with the low-GWP refrigerant R513A and is therefore A2L-ready, it can be converted to use the HFO refrigerant R1234ze, which has a GWP of less than 6, at any time – a solution that is both sustainable and extremely cost effective.

The task was to design a cooling system that is both as reliable and sustainable as possible for a computing centre in the German city of Offenbach, in cooperation with Cooltec Systems Kälte Klima GmbH. As HiRef had been using BITZER compressors for years, it came to the specialists in Sindelfingen with this project, too. As selecting a sustainable refrigerant was of key importance, HiRef opted for an extraordinary solution: for the first time, 96 screw compressors with external frequency inverters were installed in the 48 cooling systems instead of scroll compressors.

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,’ says Wolfgang Fels, Commercial Director at HiRef. 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,’ explains Fels. ‘This way, they make a valuable contribution to reducing CO₂ emissions.’ Their low water consumption with additional adiabatic cooling is another important step in the direction of sustainability.

Industrial refrigeration systems must be reliable and run efficiently, while meeting increasingly strict requirements in terms of their environmental compatibility. That is why HiRef designed the system with the low-GWP refrigerant R513A (A1-certified with a GWP of 573), an effective and environmentally compatible alternative to conventional refrigerants. One special feature is that the screw compressors are already preconfigured so that the user can switch to the refrigerant R1234ze at a later date. R1234ze has even less of an impact on the greenhouse effect, is not toxic, is moderately flammable and has a GWP of less than 6. The low GWP reduces the frequency of the mandatory leak checks required by the F-Gas Regulation, which has a positive effect on operating costs. ‘Environmental protection and efficiency go hand in hand here and set an example,’ sums up Pietro Trevisan, General Manager at BITZER Italia. ‘The excellent environmental properties give operators of the system more peace of mind in terms of refrigerant and device price stability, as well as long-term availability.’

Every system has a cooling capacity of 200 kW and is fitted with EC fans with optimised free-running wheels. A special high-efficiency crossflow heat exchanger with an epoxy coating makes the system extremely resistant. 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 tremendously and 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 greatly reduce sound on the exhaust air side.

The first phase of the system was completed in summer 2020. The system went into operation in November 2020, following a trial phase in October. ‘The use of screw compressors instead of scroll compressors for the first time posed extraordinary challenges that required a high degree of expertise in this project. We are familiar with BITZER from numerous other projects and were certain that we would be able to find the ideal solution with them,’ says Wolfgang Fels of the joint project.

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