FAQs

Up to 14 % of the requirement for heat in buildings in Germany can be met with energy from wastewater. Wastewater is an energy source that has major potential in urban areas in particular. Because wherever there are lots of people, there is also a great deal of wastewater and a high demand for energy. So, supply and demand fit perfectly. If one bears in mind that the heating market accounts for well over 50 % of the ultimate consumption of energy in Germany, it becomes clear how massive the energy potential of wastewater is. The heating market is a crucial playing field for the success of energy transition.

In Europe, there are already more than 100 Therm-Liner systems in use to extract wastewater energy decentrally out of the sewer system, most of them are in Germany, in France, the Netherlands and Scandinavia. The plant sizes vary between an output range of 50 kW and 2 MW. It is forecast that even higher
heat extraction rates will be achieved in the area of district development. In the last ten years, the technology has become commercially viable and is now ready to be used as part of the heating transition. Demand has already risen dramatically in the last two years. Before this, demand in the heating market had been low
because of minimal efforts to protect the environment and the clear dominance of gas and oil. This is now changing rapidly, especially as heat pumps are thought to play a major role in the decarbonisation of the heating market. The sewer network operators are also showing increasing interest in wastewater energy. Some of them have already demonstrated the energy potential online in the form of energy maps. This means that anyone can check whether there is potential in the sewer at a particular location. It would be a good idea if all sewer network operators could provide energy maps of this type.

UHRIG’s Therm-Liner can be installed both in existing sewers and in new ones. The basic requirement is that the sewer dimension is at least 400 mm. Smaller sewers do not carry enough wastewater and the installation of the plant becomes complicated because of the size. Alongside classic gravity sewer systems there are also wastewater pressure pipes which cannot be walked through. Wastewater heat can also be recovered in pressure pipes of this type, but generally the heat exchanger must be tightened around the pressure pipe, or the pressure pipe must be replaced by a pipe section in which a heat exchanger is integrated. Pressure pipes are generally used for energy generation if the heat exchangers are installed at the same time as a pressure pipe is restored or installed for the first time. Ultimately, an individual inspection is necessary and advisable for every project.

Good locations for obtaining energy from wastewater are to be found in cities and conurbations, and also in smaller towns and villages that are close to sufficiently large wastewater collectors. Ultimately, the same questions need to be asked with every property project when considering the option of using heat from wastewater. Firstly: Where is the nearest public sewer network? Secondly: How much wastewater does it carry? Thirdly: What is the temperature of the wastewater? Some sewer network operators now provide energy maps online that you can use to check any particular location in seconds yourself. Other sewer network operators will provide this information on request. You can talk to us at any time if you want to check a location. Important: Heating and cooling with energy from wastewater is already competitive today without any subsidy. Up to 14 % of the requirement for heat in buildings in Germany can be met with energy from wastewater. In Germany energy from wastewater meets all the requirements of the Building Energy Act (GEG). In new buildings, renewable energies must be used at least proportionally to cover the heat demand. For existing buildings, the use of renewable energies is encouraged through subsidies.

Depending on the background conditions on site, the investment costs for recovering energy from wastewater using UHRIG’s Therm-Liner are around €500 to €1,000 per kW heat exchanger output. These costs include the production and installation of the heat exchangers including pipework to the drain. At locations where the conditions are good, energy from wastewater provides heat production costs of around 7 to 8 cents per kWh heat output. This is a full cost analysis of the complete technology. It includes

► Capital costs of the Therm-Liner including connecting pipes and house connection
► Capital costs of the heat pump
► Pump and heat pump electricity
► Cost of maintenance and repairs

The above amount is often compared with the pure procurement costs, such as gas tariffs. People often forget that these do not cover the capital costs of heating and the infrastructure. Many projects are now realised on a contracting basis, with the end customer being offered a fixed price in cents/kWh for heat or cold. This ensures transparency and good price stability. Customers, therefore, if they wish, have nothing to do with the operation or purchase of the plant. Instead, they are provided with heat and/or cold in a “worry-free” package at a fixed price.

Yes. Wastewater has an average temperature of 10 to 12 °C in winter and 17 to 20 °C in summer. This temperature represents thermal energy that can be used to heat buildings in winter and cool them in summer. Wastewater is a completely underestimated, renewable energy source that can make a significant contribution to climate protection in the heating market. In addition: The level of wastewater can be calculated and forecast precisely over decades, which means that the use of wastewater for energy offers a high degree of reliability. What is particularly attractive is the fact that the temperature of wastewater recovers again very quickly even after large quantities of energy have been extracted. This is due firstly to the inflow of new wastewater into the sewers and secondly to the constant uptake of ambient warmth from the ground. It is therefore possible to install a large number of plants to extract energy from wastewater in a sewer network. The only thing that is important is that the plants must be a certain distance apart. The rule of thumb is: After a wastewater heat recovery plant, a “recovery line” around two to three times the length of the plant itself should be incorporated. If a wastewater energy recovery plant is 100 m long, then another plant can be installed around 200 to 300 m afterwards.

The Therm-Liner heat exchanger is a stainless-steel module with integrated water cycle. We can install our modules in any sewer at all with a nominal diameter of at least 400 mm. The water in the module is colder than the wastewater in the sewer, so that the water in the module is warmed by the wastewater flowing over the module. This means that a heat transfer take place, although the wastewater and the water in the module are not in contact. The heat is transmitted via the stainless steel. The water, which is now heated, flows from the module through a pipe to the heating plant and forms the forward and return flow to the heat pump. Using a small amount of power, the heat pump makes the energy extracted from the sewer usable. A kWh of heat generated in this way consists of 75 % energy from wastewater, with only 25 % from electricity – this is energy efficiency and climate protection in action.

Basically, energy can be obtained from wastewater at three points. Firstly, “in-house”, secondly from the public sewer network and thirdly at sewage treatment plants. With the UHRIG Therm-Liner, we extract energy mostly from the public sewer network, as the volumes of energy are large here and there are many possible energy users nearby. The quantities of energy that can be recovered in an individual building from the wastewater are very small and so extraction would generally be uneconomical. The quantities of energy at sewage treatment plants are very large but after they have been extracted, they need to be taken to potential users. The concept of recovering energy from the sewer network is therefore a decentralised approach that aims to bring source and users together directly. This is the approach we pursue.

Wastewater is an energy source that is available constantly and in large volumes. Every day, millions of households, plus commercial and industrial concerns, pour vast quantities of heating energy down the drain in the form of wastewater. This energy can be recovered using wastewater heat exchangers and used. This makes economic and ecological sense and can boost climate protection and energy transition considerably.

Buildings can be both heated and cooled using energy from wastewater. This form of energy is already competitive. Heat from wastewater is CO2-free and represents a major opportunity for energy transition in the heating market. In Germany alone, up to 14 % of the demand for heat in buildings can be met with energy from wastewater. Wastewater is an energy source that has major potential in urban areas in particular. Because wherever there are lots of people, there is also a great deal of wastewater and a high demand for energy. Supply and demand fit perfectly.

Heating and cooling with energy from wastewater are possible in any building with a power requirement of around 50 kW or more. That is around 15 residential units. The largest system constructed to date has a heat extraction rate of 2.1 MW and supplies a district with over 450 residential units plus commercial users. Commercial buildings are also easily heated and cooled using wastewater energy. The aim is that energy from wastewater will reach a temperature of 35 to 55 °C using heat pump technology. However, there are now also many projects when energy is stored at a higher temperature. It is always a question of competition and the next best option. Wastewater heat is also particularly suitable for storage in local authority or municipal heat networks. These local and district heating networks can be both cold and hot networks.