Energy Unit 2.0: XL heat pump solution celebrates its premiere in Dortmund

24.02.2026

Source: Alois Müller Group

The XL version of the Energy Unit 2.0 has gone into operation for the first time in Dortmund.

The modular heat pump heating system was developed by Vaillant together with system manufacturer Alois Müller and has now been installed at DOGEWO21 - Dortmunder Gesellschaft für Wohnen mbH.

The project is an XL premiere: the system has a six-stage heat pump cascade and achieves a total output of around 80 kW. It is intended to demonstrate how serial heating refurbishment, high efficiency and limited space in existing buildings can be combined economically.

Serial solution for existing apartment buildings

Two apartment buildings built in 1967, each with ten residential units and around 720 square meters of living space per building, are supplied with heat. Previously, heat was supplied via gas-based central heating technology. Following the failure of a heat generator, DOGEWO21 opted for a sustainable solution that could be implemented quickly.

The Energy Unit 2.0 is industrially prefabricated ("plug and heat"), delivered ready for connection and installed outside. This significantly reduces the installation work in the building - a decisive advantage when refurbishing existing buildings.

Modular concept with optimized acoustics

The Energy Unit 2.0 consists of a hydraulic module with integrated storage and control technology and a variable heat pump module. Four sizes (S, M, L and XL) with two to six heat pumps cover an output range of up to around 80 kW.

The Dortmund XL version uses six aroTHERM plus VWL 125/8.1 air/water heat pumps with the natural refrigerant R290. Two buffer tanks, each with 800 liters, and an additional electric heater ensure operation at low outside temperatures. The expected annual coefficient of performance is at least 3.5.

Compared to the previous model, the system has a more compact design and has been acoustically optimized. Thanks to the soundproof enclosure, the maximum sound power level is 64.2 dB(A) in daytime operation. Additional sound-absorbing elements are available as an option to reduce the distance to residential buildings.

Contribution to decarbonization

By switching from gas to the heat pump system, DOGEWO21 is reducing CO₂ emissions by around 20.5 tons per year. At the same time, the energy efficiency class of the buildings has improved from F to B.

For Vaillant and Alois Müller, the project is proof that serial, modular heat pump solutions are a viable approach to decarbonizing the multi-family housing stock - technically scalable, economically viable and with short implementation times.

Further information can be found on the website of the Alois Müller Group