At the Migros factory in Meilen ZH, cinnamon stars and Milanese cookies are rolling off the production line. Not only do they spread their sweet scent, they also “heat” the houses of Zurich’s lakeside community. How this works is invisible to the naked eye, because the process takes place underground: the waste heat from the factory reaches the houses via a network of pipes under the ground.
The idea of using district heating is as clever as it is sustainable: heat that is generated, as in the case of the Migros Delica production plant, does not simply escape into the air and go to waste, but is reused. Waste heat is generated when heat is extracted from a room or a product in order to reduce temperatures.
“You can’t generate cold, you can only take heat away and put it somewhere else,” explains Markus Müller, responsible for energy management at Delica. In the case of the Migros production plant in Meilen, the heat ends up in the energy center of Energie 360°, a Swiss company that specializes in sustainable energy solutions. This energy center was built specifically on a plot of land on the Delica site. There it is brought to the required temperature level using heat pumps and fed into the local pipe system.
The necessary work began in summer 2022. The first properties have been heated with waste heat from the biscuit factory for a year now. The next stage of construction work is already underway, with 100 properties to be connected by the end of the project. These include detached houses, larger apartment blocks and company buildings. The infrastructure is built and operated by Energie 360°. The energy company has invested CHF 20 million in this project.
1,100,000 liters less heating oil
By connecting to the Meilen energy network, the properties will be able to reduce their CO₂ emissions by 3,000 tons per year. “That corresponds to over one million liters of heating oil saved,” says Kurt Rechsteiner, overall project manager at Energie 360°. For residents, heating with district heating brings further advantages, for example, not only the CO₂ levy is eliminated, but also maintenance costs and the expense of operating a fossil heating system with chimney sweeps, fire inspections and repairs. “In addition, energy costs fluctuate much less if we use local waste heat instead of fossil heating energy, where the costs are partly dependent on external factors,” says Rechsteiner.
“By connecting to the energy network, the properties save over one million liters of heating oil.”
What happens in summer?
In the warmer months, when the houses do not need to be heated, the waste heat from the factory is used to heat water for private households. However, significantly more waste heat is generated in summer than in winter, when ice cream production is running at full speed. Glaces need a lot of cold – so a lot of heat has to give way. In addition, not only do refrigeration systems have to be cooled, in which fresh food such as eggs, milk, cream and butter are stored, but the air conditioning systems also run at full speed so that the production halls do not get too hot.
This is where seawater comes into play. Seven-degree water from the depths of Lake Zurich circulates through the factory’s air conditioning system. It absorbs the room heat and heats up to 14 to 25 degrees. The unused heated water is discharged into Lake Zurich in the summer – but strict care is taken to ensure that the water at the inlet does not heat up too much and become a danger to the fish.
The refrigeration systems have also been cooled with lake water for almost four years. Thanks to this method, the Meilen site was able to save three quarters of synthetic refrigerants, i.e. chemically produced substances, in one fell swoop. This is an advantage because refrigerants are highly flammable and therefore pose a certain occupational risk. In the event of a leak, vast quantities of greenhouse gas could also escape.
Winter air meets the scent of cookies
Unfortunately, it is not yet technologically possible to store the surplus waste heat from the warm summer months until the next winter. This is because storing heat requires an enormous amount of space. In the case of hot water, this would mean huge tank systems. And even that would probably not be enough, because even the best insulation available today could not keep the heat in until winter.
At the moment, however, the cold winter air is cooling the factory halls while the Christmas cookies are baking away. Their energy will soon reach people in two ways – through the ground and through the stomach.