Background For the past 10 years much of the research into centralised refrigeration systems has examined so-called transcritical CO2 refrigeration systems, which use CO2 as a refrigerant instead of hydrofluorocarbon refrigerants (HFCs) and so have a reduced impact on global warming. This technology was believed to have the potential to achieve lower costs, energy consumption and environmental impacts. Nevertheless, although smaller examples of such systems had been developed, mainly for heat pumps and air conditioning units, the know-how required to build an economical transcritical CO2 system for larger-scale use in supermarkets was limited. Objectives This LIFE project aimed to demonstrate the environmental and commercial benefits of transcritical CO2 refrigeration systems for use in supermarkets and similar areas. The project planned to design an optimised CO2-based system and then test its cooling capacity, energy efficiency, safety and functionality at a laboratory scale. The results were expected to inform the development of a full-scale prototype. Results The project succeeded in achieving its technical objectives and the prototype developed with LIFE assistance has been shown to work satisfactorily in a commercial supermarket environment. Higher operating pressures were required for the new CO2 equipment and this involved redesigning compressor components as well as replacing traditional copper pipes with steel alternatives in the refrigerator’s cooling evaporation loops. The new technology permits manufacturing cost savings compared to HFC technology and these can be passed onto the customers without reducing producers’ margins. In addition, the CO2 technology offers lower operating costs due to the following factors: (a) Less energy consumption - monitoring showed that the energy consumption of a CO2 system is around 4% lower than a HFC system (e.g. the conventional R404a parallel system); and (b) Lower maintenance costs due to lower price of the CO2 refrigerant. These factors are estimated to lower combined purchase and operating costs by least 5%. Furthermore, the technology also provides increased reliability and safety over HFC models, in addition to improved environmental impact. Commercial opportunities are forecast to be especially strong in the lower capacity range (up to 100 kW refrigerators), due to competitiveness based on simplicity and price. The transcritical CO2 technology is considered easy to maintain and CO2 is readily available at relatively inexpensive prices, so no geographical limitations are anticipated regarding implementation of the new technology. The beneficiary estimates that transcritical CO2 technology could be used in approximately 15 million refrigeration units (condensing units, hermetic plug-in units and vending machines) throughout the EU. Other manufacturers have now also designed their own transcritical CO2 refrigeration systems and these were developed separately to the LIFE beneficiary’s work. As such, the technology is well used which has created considerable environmental benefits in terms of reduced HFC use. This will assist the HFC phase-out process in Europe and make important contributions to international conventions such as the Montreal Protocol that regulates use of ozone depleting substances. Further information on the project can be found in the project's layman report (see "Read more" section). This project has been awarded the title of "Best of the Best" from a shortlist of 22 "Best" LIFE Environment projects in 2008-2009.