Excess heat recovery from sewage water in Cologne

Location: Cologne, Germany

Population: 1,083,498 (city area)

Climate: Oceanic

Duration: 2012- 2016

Sector: District heating and/or cooling

Funding sources: Public – private

City networks:  N/A

Savings: 214 ton Carbon Dioxide Equivalent (CO2e) in Wahn and 150 tonCO2e in Mülheim.

Solutions:  The demonstrator consists of three distinct operation sites to recover waste heat from sewage water.

Multiple benefits: Energy efficiency and annual greenhouse gases (GHG) savings.

Objective – The Demonstrator in Cologne’s primary purpose is to collect surplus heat from sewage water and utilize it to power decentralized local heating networks by distributing heat and domestic hot water (DHW) to local school buildings.

Solutions – The CO1 demonstrator is divided into three operational sites: Wahn, Mülheim, and Nippes. Sewage source heat pumps are used in all locations to recover heat from sewage water. The system’s primary components are heat exchangers, water-to-water heat pumps, gas boilers, and heat buffer tanks.

Funding – Energy Supply Contracting is the financial model employed in this project. RheinEnergie AG designed and operates the building’s heat recovery system. External companies such as Vießmann (a producer of heat pumps) and URIGH (a manufacturer of heat exchangers) installed the equipment. The investment and maintenance costs are recovered through the sale of heat.

Innovation – The heat exchanger, put inside the sewage pipe, is one of the demonstrator’s distinctive features.

This indirect heat extraction approach employs two demonstrator locations (Wahn and Mülheim). At the third location, a technique known as direct heat extraction is applied. This technique implies that a portion of the sewage water is bypassed and routed directly to the heat pump’s evaporator.

Success factors – 1) The project implemented a new management control system and optimized the system’s functioning. The gas boiler now supports the thermal energy production in times of higher demand; 2) To modify the sewage pipe system at the Cologne Nippes site, a bypass method was constructed; 3) A bypass from the sewage network to the heating room was constructed to recover the thermal energy; 4) It must be considered, mainly if this is the first time, that some additional time for the permitting phase will be required to allow the appropriate authority to approve the sewage system modification(s).

Significant outcomes

• Annual GHG savings: 214 tonCO2e in Wahn and 150 tonCO2e in Mülheim;
• Energy efficiency: 116% in Wahn and 128% in Mulheim.

Synergies with local policies:

• KölnKlimaaktiv 2022. The city must avoid about 3.9 million tons of CO2 emissions each year to meet the Cologne climate protection targets; the aim is to cut GHG emissions by 50% by 2030 (relative to 1990);
• Climate Council Cologne is the driving force behind a climate-neutral Cologne. It is establishing a plan for attaining climate neutrality in the city, including ambitious to lower GHG emissions in the energy sector (among others) by 2030. Energy aims to cut GHG emissions by 62 % by 2030 compared to 1990.

Political alignment:

• Climate Action Programme 2030 sets a price on climate-damaging CO2 emissions, promotes innovation and investment, and sets legal standards. The goal is to reduce GHG emissions by 55% by 2030. The German government will support businesses create more energy-efficient technologies;
• National Action Plan on Energy Efficiency outlines the Federal Government’s Energy Efficiency Strategy for the 18th parliamentary term. Building rehabilitation and district projects that are energy efficient will contribute to energy efficiency and climate mitigation while also enhancing regional content to generate and secure jobs;
• Climate Action Plan 2050 is the driving force behind a climate-neutral Cologne. It is establishing a plan for attaining climate neutrality in the city, including ambitious to lower GHG emissions in the energy sector (among others) by 2030. Energy aims to cut GHG emissions by 62 % by 2030 compared to 1990.

Marketability: The general replication requirements for demo technologies are evaluated using seven criteria: the availability of the exploited source, flexibility to varied climate conditions, simplicity of permission, installation, operation, and necessary investment cost.

When it comes to replication potential at the European level, more than 84 % of the EU population is connected to a sewage network. A figure that rises if the analysis is limited to urban areas only; this means that the replication potential for the Cologne demonstrator is exceptionally high, thanks to its adaptability to different climate conditions and use of economically viable conventional technologies (source).