Migros Bulle (CH)

First  Ejector  IS  operating  successfully

In July 2013 the commercial refrigerating system in the modernised supermarket Migros Bulle is realised by a transcritical CO₂-refrigerating system, which sets new standards according to energy efficiency. The efficiency of this first CO₂ refrigerating system with an ejector is increased by 15% compared to common systems. The implementation of an ejector in a commercial refrigerating system draws attention. For 10 years now, transcritical CO₂ refrigerating system are experiencing a renaissance in commercial and industrial refrigeration. With the commissioning of the 327^th CO₂-refrigerating system engineered by Frigo Consulting Ltd. in cooperation with partners, a technology step has been made. By integrating an ejector into a CO₂-refrigerating system, internal losses are reduced and energy savings are achieved. Overall the refrigerating system in Migros Bulle generates 150 kW of medium and low temperature cooling capacity. By increasing the energy efficiency, 60'000 kWh electrical energy can be saved per year. This corresponds to a reduction of 9200 kg CO₂-emissions per year.

The CO₂ is circulating in a closed circuit and is compressed and expanded to several different pressure levels. While energy is needed for compression, energy is released during expansion.The implementation of an ejector allows using the energy released by the expansion and hence relieves the compressors during the compression-cycle. Liquid CO₂ in the suction line of the medium temperature compressors is separated in the low pressure receiver. Driven by the expansion energy, the ejector pumps the liquid CO₂ from the low pressure receiver back to the medium pressure receiver, from where it gets back to the cabinets. The ejector allows operating the system without a complete evaporation of the CO₂ in the cabinets. Thereby the heat transfer properties are increased tremendous and allows to increase the evaporation temperature. The increased evaporation temperature reduces the power consumption of the compressor and the ice formation on the evaporators in the cabinets and cold-rooms. Over all, the energy consumption for the commercial refrigeration at Migros Bulle can be reduced by 15%.

promising outlook

Transcritical CO₂ refrigerating systems in combination with ejector technology is considered by experts as a future technology, especially in commercial and industrial refrigeration. The ejector has no moving parts and includes just 3 connections for CO₂. The comparatively simple implementation is based on standard components. This guarantees a high operational safety and a short payback time. With the confidence of Migros Neuchâtel Fribourg and the financial assistance of the Swiss Federal Office of Energy, another milestone in energy savings has been achieved. Over one year the engineers of Frigo Consulting Ltd. worked together whit partners on the implementation of the ejector. Significantly involved was the research institute SINTEF form Norway, the rack manufacturer Enex srl from Italy as well as Alpiq InTec West AG from Switzerland which implemented the refrigerating system on site. Due to the intense cooperation between all parties, the transfer from theory into the practice was managed successfully. The remote monitoring system is providing useful data and information to optimise the operation of the CO₂ refrigerating system and the further development on ejectors.