The Austrian pilot project will take place in Liezen, 110km north of Graz, in the region of Styria. The building contains 20 apartments in a climate zone with large temperature differences between winter and summer.

The Austrian demonstration building in Liezen, owned by the project partner “Gemeinnützige Alpenländische Gesellschaft für Wohnungsbau und Siedlungswesen m.b.H.” (GWS) from Graz, was built in the early 1940s. The thermal building envelope (façades, basement ceilings, top floors, and windows) of the two-story brick residential building has undergone comprehensive renovation in recent years. However, space heating and hot water were previously provided individually for each apartment through gas boilers, individual stoves, and electric water heaters.

As part of the EU project HAPPENING, a new heating system has now been successfully installed. It consists of central air-water heat pumps, a low-temperature distribution system, and decentralized water-water heat pumps with hot water storage for each apartment. Heat distribution in the apartments is done through conventional radiators. Local solar energy is generated through photovoltaic panels on the roof. The project also includes the installation of extensive measurement equipment and a new system control, enabling comprehensive monitoring and demand-driven optimization of system operation. For instance, this allows for an optimized and coordinated operation of the PV system and heat pumps under favorable climatic conditions. This not only increases the self-consumption of the PV system but also enhances the efficiency of the entire heat supply system.

The demonstration facility will now be further optimized during a one-year monitoring phase. The performance of the overall system will be extensively analyzed, and the results will be made accessible to the public.  Read more

Climatic zone (Köppen): Dfb (Warm-summer humid continental climate)

Weather characteristics: ​

  • Colder winters (average T in January: -5,5 ºC). ​
  • The coldest winters among the three locations, with high temperature difference between winter and summer months.

Building description

Build up between ~1940.
20 dwellings in 5 sections
3 and 4 room apartments
avg. of 56m² per dwelling. ​

Ownership: The building is owned by the non-profit social housing company (GWS)

Space heating system: Varies from apartment to apartment: a) via oil or wood stove on apartment level or b) via gas heaters on apartment. Radiators are used in the apartments with a supply/return temperature of 80/60ºC.​. 

DHW System: on apartment level by electric water heaters or gas boilers​.

Existing control and monitoring System: no monitoring system installed at the moment. Basic control system in each dwelling: water supply controlled by ambient thermostats (on/off control strategy).

Space heating energy consumption: ~44,8 MWh/a​ rwsp. ~40 kWh/m2​

DHW energy consumption: 29,1 MWh/a​ resp. 26 kWh/m2​

This pilot is now fully operational and collecting data

The Liezen pilot system is currently in full operation, having been installed, commissioned, and running successfully since June 2023. A comprehensive monitoring system is actively collecting data, which will be used to refine the control strategy and optimise system performance in the coming weeks. 

Installation process

Initial data tracking provided valuable information. Unlike traditional heating system installations, this project caused less disturbance due to strategic timing, with the installation taking place during the summer months to avoid interference with the heating season. The hot water system installation was completed swiftly, thanks to excellent organisation and communication with tenants. Clear communication and proactive planning ensured a smooth process for residents and the installation team, resulting in minimal disruptions, primarily limited to short periods of tenant presence within the dwellings. 

Preliminary results

While the final energy savings analysis is still in progress, the pilot system represents a significant step towards a more sustainable future. The Liezen pilot showcases the potential of advanced heat pump technology, particularly for buildings with high-temperature variations. Preliminary results from the HAPPENING EU presentation indicate promising energy savings, reinforcing the impact of the project. 

The 4 fenced outdoor units of the air-to-water heat pumps
Indoor units of the 4 central air-to-water heat pumps in the heating central in the basement of the building