Collage: Store refrigerators and explanatpry graphic of air flow and placement of thermometer
The placement of the sensor that measures the temperature of the airflow has proved to be crucial.
Photo and graphic by: Tommie Månsson

Simple innovation saves energy in the supermarket

​Researchers at Chalmers discovered by chance that the thermometer in modern store refrigerators is systematically wrong placed, resulting in supermarkets consuming more energy than necessary. But they also figured out how to solve the problem, and the solution has great potential with possible improvements in over 3000 supermarkets – in Sweden alone.
​Tommie Månsson has recently completed his doctoral project on Supermarkets as virtual batteries in demand response systems, and during an experiment he stumbled upon something peculiar. The thermometer that regulates the cold in a store refrigerator is generally incorrectly placed, which means that it cools unnecessarily much.   
  – When stores switched from open refrigerated cabinets to closed ones with a door, they failed to reposition the thermometer that measures the outgoing air. Since the thermometer is placed too close to the door, the outgoing air seems warmer than it actually is, which makes the refrigerator lower the temperature more than necessary. As a result the fridge uses more energy than actually needed and runs more unevenly, Tommie Månsson explains.   
When the researchers in experiments moved the thermometers to a more suitable position in the refrigerators – thus showing a more correct temperature, they noticed that the refrigerators on average consumed about five percent less energy.   
  – We can see several climate-positive effects. The temperature of the air that enters the refrigerator is not as crucial, and you can maintain more even temperatures, which leads to energy efficiency. In addition, the heating needs of the stores are reduced when the coolers do not cool the indoor air as much as before, says Tommie.   
The discovery resulted in an EU patent for a holder for the thermometer in store refrigerators, which makes the thermometer easy to move and reposition inside the refrigerator, and a corporate spin-off to launch and implement the innovation in the market.   

Untapped potential   

Pilot tests in stores of German supermarket chain Rewe have been successful with a clear reduction in consumption; and an expansion of the small thermometer holder 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.   
  – They probably don’t see it as that much of a problem. In the past, the stores had open refrigerators and when you put on doors, energy consumption was more than halved – which is a fantastic improvement. So despite the fact that it can be further improved, the market seem content.   
However, Tommie believes that when you have already made the big change, it is instead the small details that become important. Swedish supermarkets account for 3% of Sweden's total electricity consumption, of which only refrigerators account for about half of of this figure. The fact that store refrigerators would be even more energy efficient could thus be of great importance for reducing energy use and thereby reducing carbon dioxide emissions.   
  – We use chilled foods to a much greater extent now than historically. So despite the fact that most stores have replaced their inefficient open refrigerators with more energy-efficient closed ones, it seems the cooling systems do not actually draw less electricity in total, because today the supermarkets have many more refrigerators than before, Tommie Månsson concludes.

Text: Catharina Björk

The article "Exploratory investigation of return air temperature sensor measurement errors in refrigerated display cabinets" was published in Springer Journal Energy Efficiency 1/2021.

Tommie Månsson is a PhD from the division of Building Technology, Department of Architecture and Civil Engineering at Chalmers. The name of the spin-off venture is ChillServices.
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Facts and figures

The collaboration with the German supermarket chain Rewe has meant that the researchers have moved 6,519 thermometers in 454 supermarkets. Based on the measurements made by the stores, these simple interventions have saved approximately 18,889 tonnes of CO2 eq, which corresponds to emissions generated by 4,216 people. In Sweden, there are around 3,200 supermarkets with refrigerators where the temperature sensors potentially are incorrectly placed.

Page manager Published: Wed 24 Mar 2021.