Case Study Detail

Flagship store with latest technology

The remodelling of the Migros branch in the Mythencenter in Ibach Switzerland is drawing to a close. During the 8 months of the remodelling work, split into 4 phases, the supermarket with its sales area of 3,900 m2 has been given a completely new appearance. Apart from the new appearance, an advanced CO₂ refrigerat-ing system is installed on site which supply’s 170 metres of medium and low temperature cabinets as well as 280 m2 of cold rooms and freezers with cooling capacity. With a so far unreached efficiency, two identical CO₂ booster units provide a total of 250 kilowatts of refrigerating capacity.
 

All good things come in threes

The significant increase in efficiency compared with conventional CO₂ refrigerating systems is attributable to three effects. On the one hand both of the CO₂ refrigerating units are designed so that all medium and low temperature evaporators can be operated ""partially flooded"". This means that the refrigerant is still partly liquid at the outlet of the evapora-tors. This increases the heat exchange efficiency of the evap-orators significantly and the product temperature can be guaranteed despite the higher evaporation temperatures. The exceptionally high evaporation temperatures of -2°C resp. -25°C compared with conventional refrigerating units with average values of -8°C and -33°C result in an enormous saving of electrical energy. A major contribution to the boost in efficiency is reached by five ejectors per CO₂ refrigerating unit. Driven by the pressure difference in the system between high- and medium pressure, the ejectors convey liquid or gaseous refrigerant. The liquid refrigerant in the medium temperature suction line receiver is returned to the medium pressure receiver from where it is brought back to the ""partially flooded"" evaporators. The gaseous refrigerant, also pre compressed by the ejectors to the medium pressure receiver, is further compressed to high pressure by the parallel compressors. The five ejectors allow the system to react to all operating conditions and load situations and ensure the highest possible operational reliability.

The combination of ejectors and parallel compressors allows to recover the energy released during expansion and to reduce internal throttling losses. Last but not least, the CO₂ refrigerating systems are cooled in the summer months by groundwater. This allows to reduce the high pressure of the refrigerating units and to operate them even more efficiently. Extrapolated for one year of op-eration, the three effects result in an annual increase in effi-ciency of at least 25%. Today the commercial refrigerating system at the Migros branch in Ibach is probably the most efficient in the world.
 

All a question of time

After the first commercial refrigerating unit with three ejec-tors at the Migros branch in Bulle, Switzerland (see Newslet-ter: ""First ejector is operating successfully“), two further CO₂ refrigerating units with each fife ejectors are now also suc-cessfully in operation. These two CO₂ refrigerating units offer the possibility of comparing different operating and control modes with one another and of identifying further optimisa-tion potential. Pioneering systems such as that at Migros Ibach involve a greater amount of engineering work for the calculation and dimensioning of components and their procurement and installation - not least because the CO₂ refrigerating units are designed so that they can be switched over to conventional operation at any time. These pioneering systems could be successfully carried out thanks to the far sightedness of the client, Migros Lucerne, and its commitment to sustainability together with the financial support of the Swiss Federal Office of Energy. Frigo-Consulting Ltd. developed the system together with Alpiq Intec West and Enex, supervised the im-plementation from the concept phase, through the engineer-ing of the system and beyond the commissioning, and is monitoring the systems behaviour very closely. We at Frigo-Consulting Ltd. are convinced that it is only a matter of time before the ejector technology becomes more widespread and will ultimately become state-of-the-art in commercial refrigeration. As soon as sufficient experience can be gained in practice, CO₂ refrigerating systems with the ejector technology will be dimensioned significantly smaller and the ejectors can be produced less expensively. It is to be expected that in the longer term, the acquisition costs for an ejector system will be below those of a conventional CO₂ system. This in combination with the significant energy sav-ings gives this technology a unique perspective for the future.
 

The role of Frigo-Consulting Ltd.

Frigo-Consulting Ltd. offers assistance in the field of innovative refrigerating systems and energy concepts for buildings:

• Design of energy concepts for buildings
• Engineering and realisation of sustainable refrigerating systems and heat pumps
• Worldwide unique innovations to save primary energy
• Training and education