CO2 Supermarkets

The journal Die Kälte und Klimatechnik has just produced an article on the opening of a supermarket using refrigeration installations for the first time running on direct expansion CO2 with both medium and low temperatures in Wettingen, Switzerland, 4 years following the opening of the first low-temperature CO2 refrigeration installation in a supermarket in Luxembourg. With a surface area of 12 500 m², this supermarket is equipped with 3 power house multi-compressors with a total refrigeration power of 380 kW, refrigerated display cases of a total length of 180 m, 9 above zero cold chambers (approximately 200 m² ground surface area) and five sub-zero cold chambers (approximately 90 m² ground surface area), all supplied by Linde Kältetechnik. The innovative aspect in this is the development of a medium temperature CO2 transcritical circuit in which CO2 is compressed to a pressure between 45 and 85 bars according to the room temperature (maximum operating pressure: 115 bars). The authors of this article also compare the use of CO2 with R-404A for this installation: operations on CO2 produce a greater energy yield for an outside ambient temperature less than 14°C; R-404A is more efficient for temperatures over 26°C; the energy efficiency for both are equivalent in the intermediate temperature range. The annual energy balance must take account of the mean outside temperature as well as the temperatures and humidity in the sales area and higher daytime refrigeration requirements than at night. The cost of investing in this transcritical CO2 process is currently marginally higher than for similar installations running on R-404A. The authors however estimate that the trend will reverse when this new technology reaches a market maturity corresponding to large quantities produced.