Residential complex in Lünen

Shift to heating with renewables in neighbourhood unit with nine blocks

The Verein zu Lünen cooperative building association (North Rhine-Westphalia, Germany) has set itself the goal of decarbonising its entire building stock by 2045. A key cornerstone of this is a neighbourhood unit project in the Brambauer district, which could be regarded as a perfect example of the shift to heating with renewables in residential buildings - from the energy efficient modernisation of the building envelope to partial self-sufficiency through photovoltaics and the installation of STIEBEL ELTRON heat pumps.

Sample heat pump project

Fully modernised, energy efficient buildings, heated with STIEBEL ELTRON heat pumps and surrounded by a park-style outdoor area: this describes a residential area some 50 years old in the Lünen district of Brambauer (North-Rhine-Westphalia, Germany). The heat pump technology in this case is part of a holistic ecological concept that is being implemented by the Bauverein zu Lünen cooperative building association in its real estate and that can be considered a precedent when it comes to energy transition. The objective is to make the Brambauer neighbourhood unit fully CO2 neutral by the start of 2024 at the latest, followed by the association's entire building stock by 2045 – an ambitious target that, in addition to extensive modernisation measures (roof, wall and window renovations; new balconies without thermal bridges; thermal insulation, heating exchange and photovoltaic system), involves no structural consolidation. Wellbeing and energy efficiency should go hand in hand.

The intended building project

In this context, it was also decided from the outset that only STIEBEL ELTRON heat pumps would be considered for the Brambauer modernisation project. This was based on the building association's many years of positive experiences with heating technology from the Holzminden-based company. Since the association's new administration building was equipped with a STIEBEL ELTRON ground source heat pump, with impressive results, the cooperative building association has been exclusively using STIEBEL ELTRON heat pumps, in most cases air source heat pumps, in all new build projects. These are now also being installed in the Brambauer neighbourhood unit. Work began in 2021 and, one year on, a total of nine buildings – spread over three blocks of three building sections each – have already been completely decarbonised and equipped with suitable heat pumps. By the time the project is complete, there should be ten more buildings, which will also be equipped with STIEBEL ELTRON heat pumps, like all of the association's real estate.

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The technology used

To cover the calculated design heat load of 51 kW (incl. DHW heating and possible power supply utility blocking times), for each of the three modernised blocks, a cascade system of three STIEBEL ELTRON WPL 25 A air source heat pumps installed outdoors has been implemented. This achieves a coverage of almost 99 percent and only needs to be supported through the use of an electric immersion heater when outside temperatures are extremely low. Using an inverter control, which enables demand-dependent control, the system only ever provides as much power as is actually required for room heating or DHW heating. Runtime compensation means that the hours run, compressor speeds and power consumption of all heat pumps in a cascade are roughly the same, which avoids a disproportionate load on individual pumps and ensures a longer system service life. To enable efficiency-optimised reduction of the flow temperatures to up to 50 °C, all heating surfaces have been replaced and centralised instantaneous water cylinders have been installed for DHW heating. A DHW circulation mode ensures the required DHW hygiene. A small electric wall mounted cylinder with minimal running costs compensates for any circulation heat losses.

Carsten Unterberg, CEO of the Bauverein zu Lünen, is confident that this project is setting the trend for the future. In the video, he talks about his experiences with STIEBEL ELTRON.

Alternative to oil and gas: air or ground source heat pumps from STIEBEL ELTRON are the perfect choice

Carsten Unterberg is satisfied with the association's collaboration with STIEBEL ELTRON: "We built a new administration building around eleven years ago and took the opportunity to install a STIEBEL ELTRON ground source heat pump - with consistently impressive results," he reports. "Since then, we have used STIEBEL ELTRON heat pumps in all new buildings in the last few years, usually air source heat pumps."

Similar heating technology solutions could be implemented in around 80 percent of all comparable existing properties across Germany. What has been achieved in Lünen serves as an example of what is envisaged with the policy for a successful shift to heating with renewables.

Data, facts and figures

Lünen neighbourhood unit


  • Lünen, Germany


  • Constructed: 1970s
  • Residential units: 120 residential units | nine buildings – spread over three blocks of three building sections each

Installed technology

  • Heat pumps: cascades of 3 or 5 WPL 25 heat pumps per block
  • Operating mode: mono mode
  • DHW backup: SHZ
  • Photovoltaic system
  • Heat load: 39 kW per block
  • Design heat load: 51 kW