Marks & Spencer trials carbon-dioxide cooling

Successful trials with refrigeration equipment using carbon dioxide have encouraged Marks & Spencer to extend the trials to further stores.
Marks & Spencer is moving to make its refrigeration systems greener with the installation of equipment from Searle using carbon dioxide as the main refrigerant to serve retail display cabinets. The carbon-dioxide circuit is cooled by a primary system using either HFC or HC. These Cascade condensing units have a capacity of 100 kW and are typically mounted on the roof. Extracted heat can be recovered or rejected to atmosphere. Robert Arthur, refrigeration manager with M&S, explains that the new units were developed as part of the group’s overall environmental initiative. ‘We wanted to explore opportunities for greener refrigeration solutions — especially natural liquid refrigerants — as there is always a risk with the HFCs and other man-made refrigerants in today’s “standard” systems. ‘Working with Searle and other partners, our target was to commission the first three CO2 systems last year. These systems have been operating satisfactorily for more than six months, and we are extending the trials to further stores this year. After that, we should have a clear indication of where our refrigeration policy should go. ‘We have over 500 stores, and most of the refrigeration equipment we buy has a life of about 20 years, so decisions we make now have major implications for our business over the next two decades.’ Nick Smith, senior development engineer with Seale, says that the Cascade systems were developed to keep capital and operating costs with the range of comparable ‘standard’ systems. Cascade systems incorporate special components such as the CO2-to-propane heat exchanger and pump station, a special propane compressor pack with inverter drive and energy-efficient EC fan condensers. In the second stage of the Cascade system, low-temperature cooling for freezer cabinets and cold rooms is provided by CO2 sub-critical systems which supply 7.4 kW of cooling with a COP of 3.0. Compared to similar R404A systems with a COP of 0.94, the new LT CO2 systems use less than a third of the energy. The sub-critical system uses just 25 kg of refrigerant.
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