SEARLE Manufacturing Company, with its 100kW condensing units, is delivering a potentially greener cooling solution for Marks & Spencer food halls.
The new cascade units, which use either HFC or HC with CO2 as refrigerants, are described as among the most powerful for any commercial supermarket application in the UK. They are being rolled out to M&S sites this year as part of a trial to establish the group's future policy on refrigeration and choice of refrigerants.

The Searle CCU-100-ECI-CO2HC cascade units, typically roof-mounted, chill and circulate CO2 to maintain cool temperatures and protect food products in the retail display cabinets on the shop floor. The CO2 circuit is in turn cooled in the cascade unit by a primary refrigeration system. Heat extracted by the cascade process may be recovered or rejected to the atmosphere.

Robert Arthur, M&S refrigeration manager, says the new units were developed as part of the group's overall environmental initiative. He says: '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, Searle's senior development engineer, says the cascade systems were developed to keep capital and operating costs within the range of comparable 'standard' systems - but with a reduced environmental risk because CO2 occurs naturally. With a similar power requirement to a Searle standard CCU R404A system of equal capacity, a CO2 cascade unit would have minimal impact on the environment should a release of refrigerant occur - equal to just 0.38 tons of CO2.

The 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 a second stage of the cascade system, low temperature cooling for freezer cabinets and cold rooms is provided by CO2 sub-critical systems which supply 7.4kW of cooling with a coefficient of performance (COP) of 3. Compared to similar R404A systems with a COP of 0.94, the new LT CO2 systems us e less than a third of the energy. The sub-critical system uses just 25kg of refrigerant.

Searle Manufacturing Company
01329 823344