Reverse Refrigerator Principle – Knowing SWR

One of the largest river heat pumps in Europe is being built in Mannheim. From 2023 it will provide climate-neutral heat from the waters of the Rhine. We explain technology and its capabilities.

According to Mannheim-based MVV Energie AG, the river heat pump is one of five large heat pumps currently being built in Germany. After the groundbreaking ceremony in early April 2022, from 2023, heat from the waters of the Rhine is scheduled to be used to generate area heating.

The MVV estimates that enough heat can be obtained from the Rhine and Neckar in Mannheim alone to supply 50,000 households. The Environment Minister of Baden-Württemberg, Thekla Walker (the Greens), spoke of an important success in climate protection in the region and in the state at the beginning of the construction of the pilot plant.

“The project is an example of how we can generate energy step-by-step in a climate-friendly manner and thus reduce our dependence on fossil fuels.”

But how does this pump work?

Harnessing heat from water or air

In principle, a heat pump is similar to a refrigerator, but it is inverted: cold on the outside and warm on the inside. It extracts a little heat from the air or water and “pumps” the temperature difference.

How does a flow heat pump work? With electricity, the heat from the river water is converted into heating for heating.

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MVV Energy AG

Even 10 degrees cold water can emit two degrees, and if you draw enough water through the system, you can heat the house with it. The pump needs electricity as input, but converts it to two to four times the heat energy.

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Water as an environmentally friendly source of energy has a number of advantages

Core heat often comes from the surrounding air. But in principle, water is more convenient and running water is really great. Because rivers keep supplying new water, ie warm water, and move cooled water away again for free. Zurich City Hall has been heated by a heat pump since 1938, using the Limmat River as an energy source.

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Heat by flushing the toilet?

Another practical application is heat recovery from waste water. The principle also works well with this one. Mannheim in particular already has two such projects. Because there is a lot of thermal energy in residential wastewater, for example when you think of hot water flowing from dishwashers and washing machines, or hot water from a shower and even flushing the toilet, it offers a lot of potential.

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You can also use the sea. Stockholm does this on a larger scale and the output is greater, for example, from the Rhine power plant in Evesheim. Rivers are ideal sources for heat pumps. They constantly supply fresh water and transfer cooled water free of charge.

The pump uses electricity to generate several heat energy

In Mannheim, the plant’s heat is scheduled to produce 20 megawatts. This equates to heaters in about 1,000 to 2,000 homes per family. It is said to generate 2.7 times more heat than one kilowatt of electricity.

Heat pump (Photo: IMAGO Images, IMAGO / Westend61)

Whether from air, river water or waste water: heat pumps must provide twice as much energy as electricity as heat.

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Some issues still need to be resolved

However, it is not entirely without problems. River dirt, erosion and winter ice: Experience from other places shows that there are technical problems to overcome. And in Esslingen, a heat pump was built in Neckar almost 50 years ago. They closed it 10 years ago. The reason: Unlike other rivers, the Neckar has not only gotten warmer, it has gotten colder, despite the climate change. Without the waste heat from coal and nuclear power plants, the plant is no longer profitable.

Großkraftwerk Mannheim AG GKM's river heat pump scheme on behalf of MVV (Photo: SWR)


Energy supplier MVV also describes the Mannheim Flow Heat Pump as a true laboratory where knowledge and know-how is gained for more pumps in the future.

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