Today, natural gas is the main source of heating in central Europe, which causes large carbon dioxide emissions. In Sweden, district heating from biomass dominates, such as branches, tops and chips from the forest industry, followed by waste heat (which arises in industrial processes) and waste incineration.
Using water as a heating source can be an interesting alternative, say sustainability researchers Sara Brogaard and Barry Ness. They are part of the research project, WaterWarmth, that explores barriers and opportunities for large-scale use of water energy, so-called aquathermal energy. They work specifically with how actors can implement pilot heating projects through analysing and rules and regulations surrounding access to aquathermal energy. According to the project's estimates, about 18 percent of Europe's buildings could be heated with aquathermal energy, an increase from today's less than 1 percent.
Extracts heat from lakes, rivers or oceans
Aquathermal energy extracts energy from lakes, rivers or oceans via heat pumps, in closed or open systems. The technology is similar to that used to extract heat from air, ground– or groundwater, but instead uses the thermal energy stored in surface water. The energy can be used for heating in winter and cooling in summer.
"The biggest advantage of using water instead of air as a heat source is that the water temperature in winter is higher than the air temperature, which gives a higher efficiency. In addition, heat transfer from liquids is easier than heat transfer from air, which further increases the efficiency of seawater heat compared to air-to-air heat pumps," says Sara Brogaard, senior lecturer at Lund University Centre for Sustainability Studies.
Another advantage is that the technology, in contrast to an air-source heat pump, does not require an outdoor unit to be installed next to the house. These units can be perceived as bulky and also make a lot of noise, the researchers point out. Furthermore, closed-loop aquathermal heating systems have a longer lifespan than air-based heat pumps or geothermal heating systems.
Can make Europe less dependent on imports of natural gas and strengthen heat resilience
The technology is also environmentally friendly, unlike natural gas, which is currently imported into central Europe from countries such as the USA and Norway. Before the large-scale invasion of Ukraine in 2022, Russia was the largest exporter.
“When it comes to changing the heating system, Europe still has a lot to do. Aquathermal heating is an environmentally friendly alternative that has the potential to make Europe more self-sufficient and reduce the need to import fossil fuels. Alternative heating systems, and how people can access them, are pressing issues in today's volatile geopolitical climate" says Barry Ness, senior lecturer and Director at Lund University Centre for Sustainability Studies.
In Sweden, aquathermal energy could also support a reduction of the biomass currently used for heat. This biomass could instead be utilised by other sectors, according to the researchers.
“Large amounts of biomass are burned and competition for biomass is fierce. If we can use some of the biomass for other purposes, more forest can remain for continued storage of carbon dioxide in living biomass and soil. This would be good for both biodiversity and water storage. Forest resources can also be used to manufacture climate-smart wood products or replace fossil-based plastic in industry”, says Sara Brogaard.
Why is the technology not being used on a larger scale?
Sara Brogaard and Barry Ness outline several reasons that they have identified in their research.
A key aspect is that the buildings making use of the energy must be located relatively close to water, preferably no further than a couple of hundred meters away: if the distance is too far, the water cannot be converted into energy. Another is that many European countries, such as Belgium, still subsidise fossil fuels. A third is that the technology is not well known and thus regulations and guidelines are also unclear. In many parts of Europe, the companies that work with installation and maintenance are few. This is directly linked to the fact that energy and climate policies often change, making companies hesitant to invest in new forms of energy.
In Europe, it is also small groups of citizens or organisations (so called energy communities) that initiate aquathermal energy projects, and they often lack the capacity or financial buffer to bear the risks associated with, for example, feasibility studies and initial project development.
Confident that the technology can make a difference
Despite these obstacles, the researchers are still confident that the technology can make a big difference in the long term, not least because of the increasing need to transition the heating system away from fossil fuels. Within the project, it is currently being tested in the Netherlands, Belgium, France, and Denmark. The evaluations show that aquathermal energy works well for heating everything from individual houses to small or large heating networks.
“The more communities that use the technology, the greater the incentives to implement it on a larger scale, even if it of course does not work everywhere. It is also about giving citizens a greater influence over their own heating,” says Barry Ness.
Learn about the small-scale pilots developed by the project WaterWarmth
Read more about the project WaterWarmth on the project website
