Sewer Heat Exchanger - The Predominant Way To Perform The Heat Transition!



Johannes Claren

Johannes Claren

Betül Coban

Betül Coban


Technische Universität Kaiserslautern (TUK)

Technische Universität Kaiserslautern (TUK)


Katharina Spraul

Katharina Spraul

Julia Anna Hufnagel

Julia Anna Hufnagel

Global Goals

7. Affordable and Clean Energy 11. Sustainable Cities and Communities 12. Responsible Consumption and Production 13. Climate Action 17. Partnerships for the Goals

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Heat energy accounts for a large share of total energy demand and is therefore crucial for the successful energy transition.

Sewer heat exchangers use the heat from wastewater in sewers to make it usable for building services.

This means that no fossil energy resources are burned, and CO2 emissions are saved, contributing to SDG 7, 11, 12, 13, 17.

In addition, intelligent plant systems can be created, which are also economically useful and more profitable than conventional heating systems.


Today, there are already very efficient heat pumps that operate at two temperature levels. In this case, energy is transferred to the heating circuit through a heat supply. To achieve this heat supply, the UHRIG Group has developed a sewer heat exchanger, the Therm-Liner, which can extract heat from wastewater instead of extracting the heat from generally used colder air.

By that, the company makes an important contribution to the societal energy transition, as the innovation is a more environmental-friendly alternative to conventional heating methods such as boilers, cogeneration units, etc.

The UHRIG Group is a family-owned German company that deals, among other things, with sewer construction and energy from wastewater.

Rouven Zeus, business developer of the UHRIG Energie GmbH, explains their innovation as follows. The Therm-Liner was an internal development, which stands under permanent adjustment. It consists of stainless-steel plates, through which a liquid flows. These plates are installed at the bottom of a sewer. When wastewater in the sewer flows past the sewer heat exchanger, temperature equalization of the two fluids occurs. In this process, the liquid in the plates is heated by the heat of the wastewater and then transferred into the building. In addition, the Therm-Liner can also be used to cool a building, if the temperature of the fluid in the plates is higher than that in the wastewater.

The panels are usually installed in an existing sewer, which means that the wastewater flow has to be diverted. For this purpose, concepts have been worked out to divert the wastewater, such as internal dewatering or bypass. Besides installation, maintenance is also an important issue. Since the stainless-steel plates are not damaged by wastewater, the plates can be cleaned along with the ordinary sewer cleaning and there is no extra effort.

Since 2007, the UHRIG Group has been installing the Therm-Liner in sewers and the installation quantity has progressively increased over the years. Since 2018, the Therm-Liner has been marketed in a separate company, UHRIG Energie GmbH, within the UHRIG Group.

One example of the application of this innovation is the Marchivum, which is the city archive of Mannheim. In order to be able, to look at the Therm-Liner in the application case, we conducted another interview with Michael Claren, managing director from UNITEC GmbH, who was responsible for the design of the heating system in the Marchivum.

Sewer Heat Exchanger - The Predominant Way To Perform The Heat Transition!

technology of the sewer heat exchanger system


According to Rouven Zeus, there were already first pilot projects from other companies on sewage treatment plants since around the 1970s, which first dealt with this topic. There, the heat exchange could be explored and over the years, the idea of generating energy from wastewater has come up again and again.

Since the UHRIG Group is a specialist in sewer construction, they saw their great potential to tackle the topic themselves. Since 2005, the UHRIG Group has then also dealt with it. However, they did not only want to extract the heat energy at a sewage treatment plant but also decentralized the city’s sewer network in order to make the heat usable for the city’s population.

The task was thus to develop the idea of the heat recovery from wastewater into an innovation accessible to city inhabitants and the result was the Therm-Liner sewer heat exchanger.

Motivation is always a crucial factor. Rouven Zeus was inspired by three things: "On the one hand, the sustainability idea of reducing the company’s CO2 print, then push the heat transition forward and what you certainly can’t deny, of course, is a certain technical enthusiasm for the concept itself, to drive this innovation forward and offer a technically interesting project."

Overall impact

Together with the innovative heat recovery technology, it also requires a system in the building technology, that can use the recovered energy to heat a building. A heat pump is particularly suitable for this, explains Rouven Zeus. "The flow temperature and the temperature in the heating circuit is in general lower than in a boiler system. In boilers, pellet heatings, and cogeneration units, you usually heat up the water to around 65°C. Then it flows through small radiators in the building rooms. Indifference to that, with a heat pump you want to work more efficiently on a lower temperature level and the way the plant works. This means you choose for example underfloor heating with 35°C."

Taking a look at our application case, Michael Claren shows the exceptionality of the project: "Since this was a renovation of an old high bunker from World War 2, the planning process was not an everyday task." The fact that the Therm-Liner is used for heating and cooling in the Marchivum is primarily thanks to Andreas Schmucker (the architect) and Mr. Mauritz from the city drainage department. They had the idea to implement a sewer heat exchanger in Mannheim already for a long time, so continues Michael Claren.

In the pictures, you can see the flow through which the energy passes. Mr. Claren explains to us exactly what happens there: "During winter months, heat is extracted by metal panels in the sewer heat exchanger. This heat is fed to the heat pump. The heat pump uses electric energy to raise the warmth level from approximately 8°C to 36°C. The warm water is guided to the heat panels. In the cooling process, this is reversed. Warmth is led away from the building rooms with approximately 22°C and then cooled by the heat pump to 16°C. The waste heat is guided into the wastewater through the sewer heat exchanger."

As a result, it can be said, that the innovation sewer heat exchanger also requires innovative application concepts to be made usable as a heat source in building technology. Mr. Claren also says, that it is important to build a controllable system since the incorrect operation can quickly become an energy guzzler. To check this, online monitoring was carried out at the Marchivum, where the system data could be read out continuously. Furthermore, it also requires good communication between the parties involved to achieve an economical and sustainable plant.

Business benefit

For the UHRIG Group, generating energy from wastewater and driving forward the heat transition was a good way to reduce its own CO2-footprint. As in, how Rouven Zeus says, "CO2-intensive construction industry", it is important for them to push the heat transition in order to make their own contribution to climate protection.

In addition, the company’s own competencies were expanded and a new business area was opened up. Thus, the company has a unique selling point, which creates synergy for the other business areas.

Furthermore, it was an interesting project due to the technical enthusiasm for the concept, according to Rouven Zeus. In order for the heat transition to continue and for more Therm-Liners to be installed economically, the UHRIG Group demands that policy shall intrude on ambitious measures.

Social and environmental benefit

The Therm-Liner is suitable from a water quantity of 10 l/s. This corresponds to approx. 5000 inhabitants, which must be connected to the sewer before installation. In addition, the building should have a heat demand of approx. 25 kW. This corresponds to about 10 residential units. When these conditions, from the UHRIG Group, are fulfilled, a Therm-Liner can be implemented economically in most cases. Thus, it can be a more favorable heat source than conventional heating methods.

With these conditions, about 5-14% of the building heat and warm water demand in Germany could be provided by wastewater heat, according to the UHRIG GmbH.

The Enervis study "Energie aus Abwasser: Das bislang unentdeckte Potenzial für die Wärmewende." from 2017, estimates that according to their valuation of 14%, that the potential in the year 2020 stands at 100.9 TWh per year. Furthermore, 35 TWh will be realized by 2030, so the study. Moreover, the study shows, that industrial waste heat diverted into the sewers, could raise the potential by a factor of 1.79. In addition to this heating potential, the cooling potential is 14 TWh and the demand for building cooling is increasing.

In our application example, the Marchivum, the entire building is supplied with wastewater heat at 60% of the building load. According to Michael Claren, about 600 MWh of heating capacity and 200 MWh of cooling capacity have already been achieved through the Therm-Liner. Because, conventional heating methods use oil, gas, or coal as energy sources, it consequently saved fossil fuels. For the environment and city inhabitants, this means that fewer pollutants and CO2 are emitted into the air, thereby also curbing climate change.

Furthermore, this energy generation has a high level of acceptance by the general public, since it does not disturb nature or the cityscape and requires no big space outside the sewer.

In addition, because of the cooling by the Therm-Liner in summer, the cooler is not necessary, which was an additional cost-saving at the Marchivum.

So far, more than 90 plants have been installed, resulting in annual savings of 10000 tons of CO2, compared to fossil power mix in the German power mix. This is equivalent to the emissions of 5000 average passenger cars per day, according to the UHRIG Group.

With the plants that could be connected by 2030, a saving of 10.7 million tons of CO2 would be possible, assumes the Enervis study.


Rouven Zeus, Mr.

Michael Claren, Dipl.-Ing.

Photo of interviewee

Business information



Geisingen, Baden-Württemberg, DE
Business Website: https://uhrig-bau.eu
Year Founded: 1963
Number of Employees: 51 to 200
The UHRIG Group is a family-owned company, which is now represented worldwide with its products and is involved in civil engineering, sewer network, sewer network management, sewer rehabilitation, energy from wastewater, and compressor construction.

Sustainability and environmental protection are important claims for the company. In addition, the UHRIG Group aims for being CO2-neutral and wants to guide the heat transition. Therefore, they developed the sewer heat exchanger, work with electronic dredgers, use car-sharing, and also are in a collaboration to survey a prototype of a construction site battery.