Last week the Green Cooling Council welcomed the opening of the Docklands Safeway Supermarket in Melbourne, heralding the development as having established a new standard in reducing the environmental footprint of food retail facilities.

The announcement by Woolworths that all supermarkets built from next year will be Green stores is a hugely significant development in the refrigeration industry. This lead will greatly accelerate the uptake of less environmentally harmful refrigeration and air conditioning systems across the retail sector.

Adopting CO2 (R-744) refrigeration systems will make a substantial contribution to beginning to reduce greenhouse gas emissions from the supermarket sector. The following note explains how.

Background – Cascade and Transcritical CO2 supermarkets explained

The Docklands Safeway supermarket in Melbourne is one of seven green stores that are being built with the assistance of $2 million Greenhouse Gas Abatement Program funding from a Federal Government grant to the Green Cooling Council (formerly the NRTB) to reduce the use of hydrofluorocarbons (HFCs) in the commercial refrigeration industry.

The use of carbon dioxide as a refrigerant is a huge step towards environmentally sustainable supermarkets because it avoids or greatly limits the use of hydrofluorocarbons. These are very potent global warming gases, which are thousands of times more powerful global warming agents than CO2, and which leak at about 23% or more of the very large charges (800-1000 kg) used in conventional direct expansion systems.

Because supermarket owners will shortly be obliged to report these emissions under the National Greenhouse and Energy Reporting Act requirements, and to pay for them under the emissions trading scheme from 2010, there are now strong economic as well as environmental reasons for the use of CO2 as a refrigerant.

CO2 may be used in either transcritical or cascade supermarket refrigeration systems. Both systems use CO2 as a refrigerant gas inside the freezer and refrigerated display cabinets to take heat from the cabinet and reject it to the environment.

There is much greater industry experience with the use of cascade systems, which in addition to the CO2 refrigerant circuit, need another refrigeration system to cool down the CO2 refrigerant and reject this heat to the environment via condensers on the roof. This high stage refrigerant system in a CO2 cascade system currently uses HFC 134a, which has a lower Global Warming Potential of 1400(GWP) than HFC 404a used in conventional systems, and uses a much smaller refrigerant charge in a much more leak-tight system.

Cascade systems thereby reduce the potential for direct refrigerant leakage by around 95% compared to conventional systems.

Transcritical CO2 uses the refrigerant in a way that avoids the need for this additional refrigeration system, and operates using CO2 only in all parts of the refrigeration system. It is a more advanced system because it completely avoids the need for HFCs and delivers theoretically higher energy efficiency. The Angle Vale store in Adelaide is the only such store in Australia and will demonstrate how well transcritical CO2 can perform in high ambient temperatures.

Many thousands of cascade systems are in use in Europe, and around 100 transcritical systems. In Australia, supermarket owners have made their intentions to build only CO2 supermarkets very clear. Cascade systems are now well established and accepted by the major operators, and there is great interest in the potentially superior performance of transcritical systems.