The Smart City Baumgarten project in Vienna stands as a pioneering example of how collaborative retrofitting and innovative energy systems can transform urban neighborhoods. This multifaceted initiative combines historical preservation, cutting-edge technology, and community-driven action to significantly reduce carbon emissions and future-proof residential infrastructure.
A Diverse Urban Landscape
The project focuses on four residential buildings of varying ages: one constructed in the 1980s, another from the 19th century, and two newer constructions. Each presents distinct challenges for energy retrofitting. Notably, one older building lacked sufficient land for geothermal infrastructure—a challenge ingeniously resolved through cooperation with a new adjacent construction.
Leveraging New Builds for Geothermal Potential
During the development of the new building, land was allocated for the installation of 25 geothermal boreholes, each 150 meters deep. This was more than required for the new building alone. These additional boreholes now supply heating to multiple buildings via an advanced 5th generation (5G) district heating network. Nearby buildings are also being prepped for future integration, highlighting the modular and expandable nature of the system.
A Simple Yet Powerful System
Despite the technical connotations, the geothermal system itself is relatively straightforward: polypropylene pipes circulate water through the boreholes, harvesting heat from the earth. Warm air harvesters further support the system by recharging the boreholes during summer months.
Retrofitting for Efficiency
The 1980s building is undergoing deep energy retrofitting to meet Passive House standards. Photovoltaic (PV) panels are being installed on both the facade and roof, and tenants have the option to install heat recovery ventilation systems, which can retain up to 80% of indoor heat. Traditional gas boilers are being replaced with two centralized heat pumps, and a new water piping system ensures efficient heat distribution throughout the apartments.
Financial and Operational Feasibility
Various cost scenarios were assessed, ranging from minimal intervention to full retrofitting. While comprehensive retrofitting involves higher initial investments, the long-term monthly costs are comparable to those of existing high-operation-cost systems. The project’s message is clear: invest more upfront to achieve long-term savings and sustainability.
Community Leadership and Cooperation
A key factor in the project’s success was strong local leadership. Mr. Lang, a property owner and consultant, played a crucial role in motivating neighbors and coordinating stakeholders. This initiative led to the formation of a legal cooperative that manages the shared geothermal infrastructure. Although it’s unclear whether the cooperative qualifies as an official EU energy community, it functions similarly by pooling resources and decision-making.
Public Funding and Changing Policies
Approximately 40–50% of the project’s costs were subsidized through national and municipal funding. Interestingly, funding eligibility criteria have evolved—buildings no longer need to be connected to a district heating grid to qualify. This shift acknowledges that waiting for grid extensions can delay urgent decarbonization by a decade or more.
The Importance of Space and Initiative
The availability of a nearby brownfield site for borehole drilling was crucial. Without this space—or the proactive initiative of stakeholders—the project might not have been feasible. In more densely built areas, cities like Graz have allowed boreholes to be drilled under public sidewalks and pavements, though this requires navigating complex regulations.
A Blueprint for Urban Decarbonization
The Smart City Baumgarten project serves as a model for future urban decarbonization. It demonstrates that with foresight, cooperation, and public support, even older buildings can be transformed into low-carbon, energy-efficient homes. By combining modern geothermal systems, 5G heat networks, and resident engagement, Vienna is charting a practical path toward climate-neutral cities.
