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Mannheim, a city in Germany, uses frozen water to heat thousands of houses. As interest in the idea grows, DW correspondent Tim Schauenberg decided to test it out on the Rhine River.
Midway through January, I stand in my swim trunks on the banks of the Rhine River in Germany, dipping my toes into the cold water. I’m not a swimmer who can handle all kinds of weather, and this wind is doing more than just adding to the chill; it’s also making me doubt my determination.
So far on my trip, I’ve felt that getting my hands on some chilly river water has helped me make sense of the phenomenon I’ve come to investigate: how a frigid river can provide heat to thousands of houses.
Even though it’s no longer felt necessary, I decide to brave the icy water nonetheless since it’s too late to turn back now. Taking baby steps with ginger. As I wait for the endorphins that I’ve heard would kick in once I’m underwater, a tingling sensation spreads across my body.
However, they are still not here, so I am left to experience misery instead of ecstasy and to limit my time in the cold water. I can now put a number on how chilly the river is.
As I defrost and try to get my toes to thaw, I can’t help but stare over to the other side. The idea that 3,500 flats are heated with the same water seems unbelievable. Still, there are, thanks to a massive power plant run by MVV, a provider of electricity to municipalities.
Switching to river heat from coal
Felix Hack, the project manager of MVV, gives me a tour of the building a little while later.
According to Hack, who elaborated, “Millions of liters of water flow through the Rhine,” and the river itself carries enough thermal energy to heat Mannheim many times over, even in the dead of winter. “It’s now 6 or 7 degrees Celsius [44 Fahrenheit], so physically there is still enough heat in it.”
The Rhine River and a coal-fired power stationThe Rhine River and a coal-fired power station
At now, coal is the primary fuel source for Mannheim’s heat and power.Picture: DW
Hack escorts me to a gleaming steel-fronted auditorium as smoke rises from the chimney of a coal-fired power plant. On the inside, the din is deafening.
The truck-sized heat pump is operating at maximum speed, pumping 800 liters (211 gallons) of water every second.
What are the workings of river heat pumps?
In essence, the Mannheim river heat pump is just like any other heat pump—it draws heat from either the earth or the air. Here it is, although it is somewhat larger, and the river is its origin.
The fast-evaporating refrigerant is transformed into a gaseous state by the cold water. An electric pump compresses the expanding gas, producing heat. Like a bicycle pump, this method involves keeping the valve closed while pumping continues. The water is heated to a temperature of 99 degrees Celsius (210 degrees Fahrenheit) using the heat that the pump produces, and then it is sent into the grid.
Various machinery and pipes, complemented with a gleaming silver heat pumpVarious machinery and pipes, complemented with a gleaming silver heat pump
Although the river heat pump accounts for a meager 3% of the district heating network, according to Hack, this is only the start.
“We want 50,000 households to be supplied with heat from river water,” according to him.
Two more machines are currently in the works. In addition to Rosenheim in Bavaria, water heat pumps have been installed or are in the planning stages in Berlin, Hamburg, and Stuttgart.
Lower demand compared to supply
Building and industrial heat accounts for the vast majority of global energy use, with fossil fuels providing 72% of that demand. A combination of big and small heat pumps may avoid the same amount of emissions by 2030 that all of Europe’s automobiles use in a year, according to the International Energy Agency.
At now, district heating serves fifteen percent of Germany’s buildings. However, by 2045, a significant portion of the heat might come from massive heat pumps that use geothermal energy, wastewater, or industrial waste heat to power themselves, displacing coal, oil, or natural gas.
One German researcher who sees promise in these massive pumps is Fabian Ahrendts of the Fraunhofer Institute for Energy Infrastructures and Geothermal Systems.
Germany has an abundance of environmental and waste heat that may be used by heat pumps. Ahrendts was a co-author of a research that demonstrated how this supply exceeds the demand for heat in buildings and industrial operations.
The Scandinavian nations have long relied on this technique. About 90,000 residences in Stockholm, the capital of Sweden, have been heated by wastewater from industrial processes for quite some time. Nearly half of Drammen’s 103,000 inhabitants use the thermal energy of the frigid fjord to heat their houses.
Is the river in danger?
However, there are environmental concerns with this method since the heat that is removed from the Rhine is then returned to it at a lower temperature after the pumping operation. Ahrendts warned that it may become more problematic if all the towns and industrial facilities along the Rhine were to utilize the river heat, but MVV claimed that the limited volumes of water now used in Mannheim mean that the river temperature fluctuates very little.
“Fortunately, most of our waters are overheated at the moment due to climate change, so it’s beneficial up to a point,” Ahrendts added.
German large-scale heat pump projects have been delayed despite the availability of the technology for some time. The cheap cost of fossil fuels in the past, according to Hack, is related to this.
Switching to river heat was a deciding factor in Mannheim due to municipal climate goals, state subsidies for the plant’s development, and the possibility of high CO2 taxes.
Even though I have a good grasp of the system by the time my trip is over, the drop in the Rhine is still stinging my toes. Regardless of its heat output.
