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Not only since the district heating summit last month has it been clear that the expansion of district heating in Germany will play a decisive role in the heat transition. In addition to the continuous extensions of existing networks, the expansion of new networks, there must be a strong focus on the development of renewable energy sources at all temperature levels. In our current newsletter, we would therefore like to present two articles that showcase the potential of sources that have been underutilized to date. The first article focuses on the use of treated wastewater from wastewater treatment plants for large cities. The second article takes a broader look at Europe and presents the technical and economic potential for using lakes as a heat source.
The article Comparative assessment of heat recovery from treated wastewater in the district heating systems of the three capitals of the Baltic countries by J. Ziemele et al. deals with the use of treated wastewater from sewage treatment plants in district heating systems. Absorption heat pumps are to be used for this purpose. The thermal energy of the absorption heat pump will be generated by existing biomass boilers. To quantify the potential, a three-step methodology is developed:
The methodology is applied to the three capitals of the Baltic countries. The cities of Tallinn, Riga and Vilnius already have district heating systems in operation. The length of the pipelines is between 449 km (Tallinn) and 830 km (Riga). Heat sales range from 1.64 TWh to 2.7 TWh. All three systems use CHP and boilers with biomethane and natural gas as well as waste incineration (Tallinn and Vilnius).
The result of the spatial and temporal analysis shows that the distance of the wastewater treatment plants is only a few kilometers (2 - 2.5 km) from the district heating network, so that an economic connection would be possible. Riga shows a peculiarity, where the WWTP is located in a network area with low sales. The potential in Tallinn and Vilnius is therefore estimated at 46 MW and 22 MW of thermal capacity, respectively, and only 8 MW in Riga. Thus, between 4.8% (Riga) and 20.5% (Tallinn) CO₂ emissions can be avoided. In the third step, the impact on end-user prices is investigated, taking into account different price scenarios. It is shown that in 8 out of 9 scenarios the use of wastewater waste heat decreases the end-user prices. The one scenario with no advantage is in Riga with favorable natural gas prices (2019 level).
Overall, this shows that the use of wastewater from wastewater treatment plants is a promising technology that can save both CO₂ emissions and costs. The use of electric heat pumps to raise the temperature level with a strong sector coupling to renewable electricity represents another great potential to reduce CO₂ emissions and costs.
The second article The potential of lake-source district heating and cooling for European buildings by S. Eggimann et al. describes the usable potential of lake water as a heat source or heat sink in district heating systems. The article is not limited to a few selected use cases, but rather describes the methodology to estimate the potential for all of Europe.
Similar to the first article, a spatial analysis has to be done first. For this purpose, the data from OpenStreetMaps is used to automatically filter larger lakes and the buildings in the vicinity of these lakes. Each building is assigned a heating and cooling demand via a simplified methodology using floor area and outdoor temperature. Other public sources, such as Tabula, are also used for this purpose. In a further step, possible areas that are suitable for heat supply near the lake are selected, and a roughly dimensioned heat network is integrated into these areas. Finally, the source and, depending on it, the efficiencies of the heat pumps or direct cooling are evaluated. The analysis considers the techno-economic potential, so that both energetic and cost-relevant factors are taken into account.
The spatial analysis has identified over 2000 lakes that could be used. Especially countries like Finland, Norway or Switzerland show a great potential. However, after considering the minimum lake volume and the fact that the lake may be frozen for a maximum of 1 month per year, only 171 lakes remain available for use.
If the building energy demand for heating and cooling at these lakes is taken into account, it becomes apparent that the demand exceeds the potential overall. Only 17 % of the cooling demand can be covered by lake water. If heating and cooling are considered, this value drops to 7% of the demand. The techno-economic potential of using seawater is strongly dependent on the level of electricity prices. The higher the price of electricity, the greater the potential. The article also examines the influence of utilization on seawater temperature. It can be shown with the help of simulative studies that the influence of lake water usage on the temperature of the lake is marginal.
In our last newsletter, we featured a number of reports focusing on topics such as digitization, market outlooks, and municipal heating planning. Again this month, we noticed many reports during our research that we would like to share. The large number of these reports shows how up-to-date the topic of district heating is and what opportunities can be found in a consistent expansion of district heating:
The next issue of our newsletter will be published on July 5, 2023. In the meantime, we invite you to have a look at our redesigned blog and follow us on LinkedIn.