Cool ideas

Supermarket manager Thomas Knopp likes nothing more than talking about his store's new climate-friendly refrigerators and freezers."What makes them so innovative is that our cooling systems run on natural gas and are completely chemicals-free," he says proudly.

He's not talking about a supermarket in a country with a reputation as an environmental trailblazer. Knopp doesn't work in Germany or Japan but for the 'Pick n Pay' chain in Cape Town, South Africa.

The company has installed state-of-the-art, climate-friendly freezers in two of its outlets. These rely not on standard synthetic refrigerants such as CFCs (chlorofluorocarbons) and HCFCs (hydrofluorocarbons), but CO2, a far less environmentally-damaging natural refrigerant.

But as everyone these days is well aware, carbon dioxide is a greenhouse gas and a major contributor to global warming. So how come it's now being hailed as an environmentally-friendly coolant? 

 It sounds paradoxical to the layman, but experts agree that CO2  is the answer to green refrigeration in supermarkets – the reason being that as a natural gas that can be "borrowed" from the carbon cycle, it is climate-neutral: Supermarkets using CO2 are not adding to greenhouse gases in the environment.

In contrast, standard fluorocarbons such as CFCs are molecules constructed to act as refrigerants, among other things. Their impact on the environment is measured by their Global Warming Potential (GWP).

The GWP is how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide (whose GWP is by convention equal to 1). In some cases, the GWP of fluorocarbons is 100 to 4000 greater than that of CO2.

Or, as Greenpeace puts it: "Just by releasing the 300 grams of refrigerant contained in a domestic fridge the climate impact would equal driving a Volkswagen Golf from London to Moscow."

Dangerous leakage

The 1987 Montreal Protocol, signed by almost 200 countries, was designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion, such as CFCs and HCFCs. Developing countries were given longer time-frames, with a deadline of 2010.

But when the industrialized nations phased out ozone-depleting chemicals CFCs and HCFCs and hydrochlorofluorocarbons, they replaced them with hydrofluorocarbons (HFCs). While these do not damage the ozone layer, their global warming potential is significant. Nonetheless, they remain the norm in super­market fridges and freezers – including in Germany.

One of the biggest problems with these chemicals is leakage. Virtually all cooling systems leak, but because of their smaller molecular structure, HFCs are more prone to leak than CFCs. This represents thousands of tonnes of emissions, as Thomas Knopp observed, when he still used his old cooling systems. 

"With the old systems, up to 30 percent of the cooling agent would leak," he said. "There was leakage everywhere, from the pipes to the actual shelves. Now we have no leaks at all."

Refrigerators relying on CO2, meanwhile, withstand a much greater gas pressure than standard refrigeration units. This means that state-of-the art refrigeration systems are more robust and durable. As well as requiring fewer refrigerants because they leak less, they are also more energy-efficient.

Only a matter of time

Knopp estimates that his new system uses 25 percent less energy than the one it replaced. The only downside is the higher manufacturing cost – the main obstacle preventing green refrigeration from going mainstream. Too many supermarkets are put off by the relatively high investment needed to make the switch.

But a further selling-point is the opportunity they afford for waste heat recovery, using waste heat from the refrigeration to heat the store premises or its water supply, for example. Not only does this reduce the supermarket's carbon footprint, it also reduces its energy consumption.

Given these many environmental and economic advantages, it should be only a matter of time before CO2 refrigeration systems become standard features in supermarkets. 

Emerging nations and developing countries could, moreover, learn in this instance from the mistakes of the industrialized countries.

While recent decades saw their supermarkets switch to refrigerants that do not damage the ozone layer, in the process introducing a generation of chemicals with a greenhouse effect thousands of times stronger than CO2, chains such as 'Pick n Pay' in South Africa can leapfrog this stage and go green without further ado. 

Martin Schrader, Michael Wetzel (jp)
Editor: Sonia Phalnikar