In the analysis part, different system concepts are assigned and evaluated for different apartment building types and refurbishment processes. User comfSolutions for the use of low-exergy systems are being developed for the heat supply of existing multi-family houses. The subject of investigation are electric and gas heat pumps as well as heat transfer and ventilation systems.ort, economic aspects and the reduction of emissions are decisive criteria. The heat pump systems and components developed are to be implemented and evaluated in exemplary refurbishment projects.

Around half of the apartments in Germany are in apartment buildings. The majority of the large apartment buildings dates from the 1970s. On the other hand, most of the smaller apartment buildings were built in the 1960s. As a rule, the buildings have no ventilation systems. The heating systems are used for space heating as well as for domestic hot water heating and are mainly operated with gas.

For the success of the energy transition, it is also important to secure the heat supply of these existing buildings through sustainable technologies. Heat pumps driven by electrical energy or fuels have considerable potential to reduce the specific C02 emissions for heat supply in refurbished buildings. However, this does imply special requirements for transfer systems for space heating and hot water production (heat sinks) as well as for the utilisation of environmental heat (heat source), especially if the exergy requirement for the provision of heat is to be kept low.

Research focus

In the project group "LowEx concepts for the heat supply of existing apartment buildings (LowEx existing buildings)" solutions for the use of electric and gas heat pumps, heat transfer and ventilation systems in energy-efficiently refurbished buildings are analysed, developed and demonstrated and evaluated in apartment buildings. The aim is to evolve the systems for the refurbishment of existing buildings, to increase their efficiency and to ensure safe and energy-efficient operation.

Central idea and approach

The overall project network "LowEx inventory" comprises projects for technology development and projects for demonstration and monitoring, as well as a comprehensive joint project "LowEx inventory analysis". In the technology projects, components and systems for the energetic refurbishment of apartment buildings are (further) developed together with leading suppliers of building energy technology and the Fraunhofer ISE. It is planned to use these in exemplary refurbishment projects in connection with selected heat sources, storage tanks and transfer systems.

In the analysis part of the project, the scientists examine the existing apartment buildings as well as the actors and processes involved in the refurbishment. LowEx system concepts with heat pumps are developed and analysed and evaluated with the aid of system simulations. The concepts are assigned to apartment building types and certain refurbishment scenarios. This takes into account the achievable user comfort, economic aspects and possible savings in CO2 emissions. The remediation solutions should have as little impact as possible on the residents. Finally, the monitoring results from the demo projects are scientifically evaluated and compared with the results of the simulation calculations. On this basis, the economically and technically optimal configurations for the identified refurbishment cases in the multi-family housing stock are determined from the developed LowEx systems.

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At a glance

Short title: Verbundvorhaben: SolaresBauen: LowEx Bestand
Funding number: 03SBE0001A
Topics: Climate-neutral heating, Buildings
Running time: June 2016 till February 2022


Albert-Ludwigs-Universität Freiburg, Institut für Nachhaltige Technische Systeme (INATECH)

Tel.: +49(0)761-2714-101

Karlsruher Institut für Technologie, Fachgebiet Strömungsmaschinen (FSM)

Tel.: +49(0)721-608-42350

Fraunhofer-Institut für Solare Energiesysteme ISE

Tel.: +49(0)761-4588-0