In the wake of a rise in awareness about sustainable refrigeration in the food retailing sector, supermarkets have begun to increasingly advocate the use of natural refrigerants. Eurammon tracks the trend.

THE BACKGROUND

For a long time now, consumers have not only been factoring in the quality and price when making purchases, but have also been giving a serious thought to sustainability. In the results of a study conducted throughout Germany by IBH Retail Consultants published in December 2010, 60% of those interviewed indicated that their purchase decisions have also recently started to take into account the extent to which companies implement the increasing demand in general for a sustainable approach to everyday business practice. Supermarket chains are no exception, and have started opting for environment-friendly shop concepts with lower emission rates in their stores to reduce their carbon footprint.

OPTING FOR SUSTAINABILITY

It is an established fact that refrigeration systems account for a large share of energy consumption in the food retailing sector. Possibilities for taking a sustainable approach include, among others, the choice of a particular refrigerant as against others. “Depending on the local conditions, today, it is possible to develop an individual solution with natural refrigerants for every supermarket,” confirms Mark Bulmer, member of the Board at Eurammon, the European initiative for natural refrigerants. “Natural refrigerants, such as ammonia and CO2 are used for supermarket refrigeration all over the world. In fact, there are two good reasons working in their favour: firstly, they have no or only negligible global warming potential. And secondly, supermarket refrigerating systems with natural refrigerants are energy efficient in operation.”

The type of system suitable for any particular supermarket depends, among other factors, upon its geographical location and the prevailing climatic conditions on site. Outside temperatures warmer than 26°C prevent liquefaction of carbon dioxide because the refrigerant temperature on the high-pressure side is above the critical temperature. Such trans-critical CO2 solutions, therefore, tend to be used in moderate climate zones, such as Canada, Scandinavia or Central Europe, Bulmer explains. He says: “Ammonia-CO2 cascade systems, on the other hand, constitute a suitable possibility for environment-friendly, efficient refrigeration in warmer regions. Ammonia is deemed to be the most energy-efficient refrigerant of them all.”

SUSTAINABLE FREEZING AND CHILLING WITH CO2

In 2010, SSP Kälteplaner AG developed a completely new refrigerating system for the Migros Supermarket in the Tivoli shopping centre in Spreitenbach, Switzerland, which is now in use. The refrigerating solution covers all the requirements of a supermarket refrigeration system, while taking into account the optimum consideration of the general local conditions with regard to capital expenditure and energy demand.

This is how it works: The new system consists of two 150-kilowatt combined units for chilling and a 53-kilowatt booster combined unit for freezing. Altogether eight Bitzer reciprocating compressors are used for chilling, with another four Bitzer reciprocating compressors in the booster-combined unit. Direct evaporation of the environment-friendly natural refrigerant CO2 is responsible for refrigeration distribution in chilling and freezing. Both systems operate in the sub-critical range whenever possible. Under high outside temperatures or when waste heat is called for, the combined chilling units operate in the supercritical range with a working pressure of up to 92 bar.

Additional energy savings are achieved by heat recovery. A heat pump uses the waste heat of the system to provide hot process water and heat for the supermarket and for an adjoining restaurant. The remaining residual heat is discharged outside via a gas cooler/condenser on the roof.

SUPERMARKETS IN SA TRYING OUT CO2

At present, many supermarket refrigeration systems in South Africa still use refrigerants with a high global warming potential (GWP) and in some cases, even a high ozone depletion potential (ODP). The use of natural refrigerants in supermarkets is still relatively unknown in South Africa, and has, therefore, hardly been tested. However, in view of the constant increase in energy costs of more than 20% per annum in some cases, a number of South African supermarkets have decided to change over to natural refrigerants.

In 2009, for instance, the GEA Group provided various supermarkets in South Africa with compressors for NH3-CO2 cascade systems. This is how it works: A solution of Ammonia and a glycol is used in the chilling range to keep the dairy and delicatessen cabinets and refrigerated warehouses at temperatures between 0 and +2°C. The deep-freeze circuit operates on the basis of direct CO2 evaporation for the frozen food and ice cream displays. In addition, the waste heat from the ammonia system is recovered to save energy in the process of heating water for the supermarket.

Various Grasso compressors generate the refrigerating capacity of the ammonia circuits in various supermarkets, reaching levels between 285 and 860 kilowatts. Furthermore, one particular supermarket uses part of the compressor to feed a cold water storage tank for air conditioning of the premises. To this end, a glycol loop freezes water balls in a storage tank. Outside peak times, all compressors work with the same suction capacity so that free capacities from the supermarket’s refrigerating circuit can be fed to the air conditioning system.

“Operators no longer have to revert to fluorinated greenhouse gases for supermarket refrigeration,” says Bulmer. “Applications with natural refrigerants offer a good alternative. Thanks to intensive research and development in recent years, natural refrigerants permit energy-efficient operation today in many areas. Depending on the service life, the marginally higher investment in the systems can be recuperated by lower overheads, thanks to reduced energy costs and less expenditure on refrigerants.”

Eurammon is a joint European initiative of companies, institutions and individuals who advocate an increased use of natural refrigerants. As a knowledge pool for the use of natural refrigerants in refrigeration engineering, the initiative sees as its mandate the creation of a platform for information- sharing and the promotion of public awareness and acceptance of natural refrigerants.