Right Through the City, Right on Schedule

As part of a key project to expand the district heating supply in the Hanseatic City of Bremen, a 7.5-kilometer-long district heating interconnection pipeline has been constructed through the city. Experts from Fichtner Water & Transportation handled the planning, overall site management, and on-site construction supervision for this project. The client was the district heating grid operator ‘wesernetz Bremen GmbH’. Not only the tight schedule, but also especially the densely built-up and heavily used urban space placed high demands on planning and execution. Numerous interests, technical requirements, and constraints had to be carefully coordinated and considered. This meant that, in addition to solid engineering expertise, the project also necessitated excellent coordination skills, strong communication skills, and a high degree of flexibility.

The urban area in Bremen is very densely built up. This historic Hanseatic city has evolved over time, and its limited road space is shared by cars, bicycles, e-scooters, and pedestrians, as well as trams, buses, and delivery vehicles. Even underground, the available space is almost completely occupied. A dense network of power, gas, water, sewer, and telecommunications lines runs through the ground. In light of this, the construction of a district heating interconnection pipeline running several kilometers through the city was a particularly challenging task. At the same time, the project was a fundamental prerequisite for Bremen’s planned phase-out of coal.

For many years, the coal-fired unit at the Bremen-Hastedt power plant supplied the eastern part of Bremen with district heating while also cogenerating electricity. As part of its climate protection strategy, Bremen’s utility company ‘swb AG’ ceased coal-fired power generation at the site on 30 April 2024. The decommissioning resulted in the loss of both heat and electricity generation from the coal-fired unit. The supply was replaced by the gas-fired cogeneration plant in Hastedt, which began operations in 2023, as well as by increased use of climate-friendly heat sources.

Key Project for Phasing Out Coal in Bremen

A key prerequisite for phasing out coal was the construction of the district heating interconnection pipeline between the Horn-Lehe/University and Bremen-East grids. As a result, heat from the waste-to-energy plant in the university area can meet a portion of the heating demand in eastern Bremen and ensure security of supply following the decommissioning of the coal-fired unit. Together with the new cogeneration plant, this laid the technical foundation for transitioning the heating supply to a significantly more climate-friendly system.

wesernetz Bremen GmbH, a subsidiary of swb AG, contracted Fichtner to handle the planning and overall site management for this project. Fichtner’s experts were responsible for the entire engineering of the project. They conducted a feasibility study, performed the preliminary, basic, permit, and detailed design, and prepared the contract award. Fichtner was also entrusted with overall site management, on-site construction supervision, and health & safety coordination. Despite the extremely tight timeline, wesernetz was able to complete the commissioning of the 7.5-kilometer-long interconnection pipeline between the two district heating grid areas in mid-2024 as scheduled.

But the project did not end with the commissioning: Fichtner remained closely involved during the subsequent phase leading up to the final acceptance of all construction work in 2025. During that period, numerous documents and change orders had to be reviewed, and the restoration of the surfaces, in particular, had to be closely monitored.

Technical Design and Route Alignment in an Urban Area

The new flow and return interconnection pipeline consists of two pre-insulated pipes with a nominal diameter of DN 500, in which the steel service pipe is surrounded by a thermal insulation layer and a plastic outer casing. The outer diameter of each casing pipe is 71 centimeters. This results in a required utility trench with a width of around 3.40 meters.

Planning work began in June 2018 and initially focused on the sections that were critical to the route alignment. This included the crossing of the railroad line between Bremen and Hamburg and of several tram lines and heavily trafficked intersections. In a total of six sections of the route, it was necessary to pass under existing infrastructure using the trenchless construction method. Various techniques were used to do so, including two microtunneling operations, several pipe jacking operations, and the use of tunnel shoring.

With Expertise, Creativity, and Strong Communication Skills

In addition to extensive technical expertise, the project also required a high degree of creativity and strong communication skills. During the planning and implementation phases, it was necessary to reconcile numerous different interests and requirements. A wide range of requirements from the transportation sector, local businesses, and the fire department and police had to be taken into account. Added to this were constraints imposed by aspects such as tree preservation and environmental protection, groundwater conditions, and soil characteristics. Moreover, the limited space and high density of utility lines in the urban area posed particular challenges.

At the same time, the project was under considerable time pressure, as the coal-fired unit could not be decommissioned until the new interconnection pipeline had been put into operation. With this in mind, the tender for the project – which was divided into four construction lots – was conducted in parallel with the planning approval process. A key factor in the project’s success was wesernetz’s early and transparent involvement of public agencies. Fichtner supported that process by preparing workshops and providing expert assistance during technical coordination meetings.

Responding Flexibly to Unforeseeable Situations

In the procurement process, two construction companies were awarded the contracts for the four construction lots, with one company taking on three lots and the other taking on one lot. Construction began in February 2022. Just under two years were available to complete the project and put the district heating interconnection pipeline into operation. Given the ambitious schedule, numerous construction sections were carried out in parallel – up to twelve at a time during peak periods.

During the construction phase, Fichtner provided an interdisciplinary team consisting of up to eight specialists to handle overall site management, on-site construction supervision, and health & safety coordination. The focus was on efficiently managing the complex construction processes, including overall supervision and coordination of the project’s execution, ongoing optimization of construction workflows and schedules, active management of change orders, and consistent enforcement of occupational safety requirements. Providing continuous on-site supervision of the construction work with at least three specialists enabled early identification and targeted correction of deviations, thereby ensuring compliance with planning and permitting requirements.

Fichtner continued to support the project even after it went into operation, through to the final acceptance of all construction work at the end of 2025. During that phase, the focus was on the systematic review of documentation and change orders, as well as on the restoration of the surfaces.

As is not uncommon with projects of this complexity, unforeseeable situations arose time and again during the construction phase, requiring adjustments to be made on short notice. These included, among other things, the discovery of asbestos-contaminated underground pipes, which necessitated extensive protective and safety measures. In other cases, planned road sections could not be used as intended for traffic-related reasons, as they were temporarily needed to accommodate detour traffic resulting from other municipal projects.

In such situations, the Fichtner team’s task was to find the best solution in terms of technical, construction logistics, and economic considerations, without jeopardizing the commissioning date. In many cases, decisions had to be made on short notice to avoid downtime costs and construction delays. Thanks to the good cooperation among the project partners, the continual technical dialog, and the constructive working atmosphere, we were consistently able to develop viable solutions in a timely and pragmatic manner to ensure the progress of construction.

Bremen Continues to Expand Its District Heating System: Follow-Up Order for Fichtner

Bremen has set itself the goal of becoming largely climate-neutral by 2038. In light of this, swb will be consistently pushing ahead with the further expansion of its district heating system in the coming years. Given the successful collaboration on the new interconnection pipeline, wesernetz is once again calling on Fichtner’s support for another key project. For the rehabilitation and expansion of the eastern trunk line constructed in the 1970s – a key district heating supply axis in the eastern part of the city – Fichtner is handling all services related to planning, permitting, and procurement.

June 2026