Researchers from Chalmers University of Technology, Sweden, discovered by accident that modern store refrigerators are consuming far more energy than necessary – simply because the thermometers within them are wrongly placed. But they also figured out how to solve the problem. And because supermarket refrigeration accounts for around 1.5 per cent of Sweden’s total electricity usage, with the figures in Germany and the United Kingdom being similar, the potential efficiency savings are therefore extremely significant.

Tommie Månsson recently completed his doctoral project looking at how supermarkets could function as virtual batteries in smart electrical grid systems. But during his experiments, he realised something peculiar. He saw that the thermometers which regulate the temperature of supermarket refrigerators were systematically incorrectly placed, resulting in excess cooling.

“When stores switched from open refrigerated cabinets to closed ones with a door, they failed to reposition the thermometer that measures the recirculating air. Since the thermometer is placed close to the door, the air seems warmer than it actually is, leading the refrigerator to lower the temperature more than necessary. As a result the fridge uses more energy than is actually needed, and runs more unevenly,” Tommie Månsson explains.   

When the researchers experimented with moving the thermometers to a more suitable position within the refrigerators, thus showing a more accurate temperature, they noticed that the refrigerators consumed on average about 5 per cent less energy. The potential improvements could affect over 3000 supermarkets in Sweden alone.

“We then saw several climate-positive effects. The temperature of the air entering the refrigerator when the doors were opened had less impact, and it became easier to maintain an even temperature – which is more energy efficient. In addition, when the refrigerators were not inadvertently cooling the indoor temperature of the store as much as before, the overall heating needs of the supermarket were reduced,” says Tommie.   

The discovery has now led to an EU patent for a thermometer holder for supermarket refrigerators, making the thermometer easy to move and reposition. A startup company has even been launched to market the innovation.

Untapped potential   

Pilot tests in stores of German supermarket chain Rewe have been successful, with around 7000 thermometers repositioned, leading to a clear reduction in consumption, and a further rollout of the small thermometer holders is planned. In Sweden and the rest of Europe, the market has not yet realised the potential, despite the fact that in Sweden alone there are potentially more than 3,000 stores that could reduce their consumption.  

Swedish supermarkets account for 3 per cent of Sweden’s total electricity consumption, of which refrigerators alone account for about half of this figure. The figures in Germany and the United Kingdom are similar. Improving their energy efficiency even more could thus have a huge impact in reducing energy use and the resultant carbon dioxide emissions.   

 “Probably the market has not yet realised what there is to gain here. In the past, stores had open refrigerators. When they put on doors, energy consumption was more than halved – a fantastic improvement. So the market seems content, despite the fact that it can improved yet further still.”

Tommie Månsson continues, “Refrigerated foods are of course far more widespread now than ever before. So despite the fact that most stores have replaced their inefficient open refrigerators with more energy-efficient closed ones, it seems that in total, the cooling systems do not actually consume less electricity than before, because the supermarkets today have so many more refrigerators.”

The findings were published in the scientific article “Exploratory investigation of return air temperature sensor measurement errors in refrigerated display cabinets” in the Springer Journal Energy Efficiency 1/2021.