Energy Innovation Austria

Bridges vol. 40, July 2014 / Feature Article

By energy innovation austria, BMVIT & the Climate and Energy Fund

This quarterly publication presents current Austrian developments and results from research in the field of forward-looking energy technologies. The content is based on research projects funded by the Austrian Federal Ministry for Transport, Innovation and Technology and the Climate and Energy Fund.

Innovation Meets Tradition:
Pioneering technologies for renovating historic buildings sustainably

Renovating the fabric of old, historically valuable buildings to today’s standards of energy efficiency is a controversial issue in European towns and cities. The goal is to find intelligent ways of reconciling the conflicting aims of climate protection and architectural culture. In Austria, quite a number of projects have been launched in recent years to encourage the use of innovative technologies and approaches in order to renovate valuable historic buildings sustainably.

New technologies and concepts for renovating old buildings 

Energy-efficient building technologies and renewable sources of energy are in widespread use today for new builds. However, existing buildings possess considerable potential – as yet unused – for saving energy and reducing CO2 emissions. Sustainably renovating the stock of existing buildings in city centers plays a crucial part in achieving EU and national energy and environmental targets. In European city centers, historic buildings predominate; conserving this fabric, with its cultural import, and developing it further provides an opportunity to steer urban development in a more sustainable direction.

Renovating historic buildings is an activity in which architectural, legal, social, and technical issues intersect. City centers, particularly, often pose special obstacles to innovative renovation strategies, such as rules applying to listed buildings or requirements for urban protected areas. If renovation is to be worthwhile in these difficult contexts, there is an urgent need for intelligent technical and organizational approaches that can be implemented cost-effectively and to users’ advantage.

In Austria, various projects have been launched in recent years with the aim of improving the thermal efficiency of historic buildings. Within the framework of the programmed “Building of Tomorrow” (Federal Ministry for Transport, Innovation and Technology) and “New Energies 2020” (Climate & Energy Fund), suitable technologies and strategies are being researched, developed, and demonstrated. The research findings and demonstration projects presented here show that energy efficiency and using renewable energy sources are perfectly feasible even in historically valuable buildings.


Flagship Project GdZ

A future for Austrian “Gründerzeit” buildings

A substantial portion of the building stock in Austria dates from the Gründerzeit period between 1848 and 1918; typical features are elaborate stucco façades, high ceilings, and solid-brick outside walls. In Austria, buildings of this period house 600,000 flats – close to a fifth of the total number. Until now, little use has been made of these buildings‘ energy saving potential. This is where the “Building of Tomorrow” flagship project will focus, to tackle integrated system approaches to modernizing Gründerzeit buildings. The aim here is to develop scalable renovation strategies with which to raise these buildings‘ thermal efficiency to an up-to-date standard; annual energy demand for space heating ought to be cut from around 120-160 kWh/m2 to less than 30 kWh/m2.

In collaboration with an interdisciplinary project team (Havel & Havel /social science, Manschein Managing Energy / monitoring, Österreichischer Verband der Immobilienwirtschaft / legal aspects, pos architekten / architecture, Schöberl & Pöll / structural engineering, Gemeinschaft Dämmstoff Industrie / dissemination), e7 Energie Markt Analyse GmbH is managing the project, which includes research into technical, economic, and legal issues, developing new components and implementing pilot projects. In addition, cost-effectiveness is being analyzed, sociological investigations carried out, and the buildings monitored post-renovation for energy consumption and comfort.

Making the building envelope thermally efficient

The critical aspects here are how to insulate the segmented façades and the firewalls, and how the joints between structural elements are implemented. Structured façades worth conserving can be thermally insulated only on the inside; here either conventional insolants such as mineral fiber or, alternatively, insulation panels (e.g., based on calcium silicate) can be employed. The surface-active properties of the latter enable them to adsorb moisture, store it, and release it into the air. For the key elements, thermal-bridge simulations have been carried out and the impact on element reliability (water vapor condensing out, mold developing) has been investigated.

Employing efficient heating, ventilation etc.

Ventilation systems with heat recovery to replace used air with fresh air under full control have already proved their worth in renovated buildings. Modern ventilation strategies achieve excellent energy efficiency and ensure air exchange at controlled rates, resulting in an agreeable indoor climate. With their high ceilings, buildings from the period between 1848 and 1918 are ideal for installing ventilation systems.

Apart from technical issues, a comprehensive strategy must also take economic, social, and legal aspects into account. Experience gathered and tentative solutions have been documented in the course of the project. A guide to implementing the renovation of a Gründerzeit building in practice covers all relevant facets for interested parties such as owners, property managers, and planners.


A future for “Gründerzeit” buildings: Demonstration projects

The demonstration buildings renovated in the course of this flagship project reflect the wide variety of building functions in the period between 1848 and 1918. As well as purely residential buildings, mixed-use buildings (residential use plus offices) were included.

Kaiserstraße: Ambitious renovation in compliance with rules for listed buildings

This listed building is part of a complex belonging to the Order of the Lazarites; a conservation order applies to the façade, which features exposed brickwork. It was essential that renovation leave the façade and the building’s roof cladding largely intact. To improve the thermal properties of the building envelope, interior insulation panels were fitted to the listed façades. The roof timbering had to be reinforced structurally; the roof cladding was not affected by renovation.

The annex and the courtyard façade were renovated very successfully (U-value approx. 0.15 W/m2K), using outside insulation. The outside casements of the Viennese box-type windows were renovated in line with conservation rules, and wood-frame windows were fitted inside to yield a result complying with zero-energy building standards. A central ventilation system with heat recovery ensures a satisfactory rate of air exchange in all rooms in which people spend time. As the building was already connected to the district-heating grid, no changes were made here. When renovation was completed in the summer of 2013, unit heating energy demand had been reduced by around 80 percent.

Eberlgasse: First-ever renovation of a “Gründerzeit” building to Passive House standard 

When this building (erected in 1898, damaged in the Second World War and later rebuilt) was renovated, the focus was on achieving Passive House standard. The building’s compact structure and its location wedged between other buildings were definite advantages here. Renovation was carried out in close cooperation with the tenants living in the building and was successfully completed in the autumn of 2013.

In order to achieve Passive House standard, a composite thermal insulation system was fitted to the outside of the façades facing street and courtyard. The vaulted ceiling in the cellar was insulated, and top-grade windows and doors to Passive House standard were installed. The innovative features of the building include a central ventilation system with ultra-efficient heat recovery, the groundwater heat pump, and photovoltaic equipment. The entire electrical system, heating, ventilation etc. were replaced and energy-efficient lighting was fitted, which saves even more primary energy. The energy balance sheets computed for the building show that after renovation it qualifies as a zero-energy building, and that savings of more than 80 percent can be anticipated with respect to heating energy demand, end-use energy demand, primary energy demand, and CO2 emissions.

David’s Corner: Comprehensive strategy for renovating a group of “Gründerzeit” buildings

This group of three buildings forms the corner of a typical perimeter block development in Vienna; one of the buildings has a segmented façade worth conserving.

The goal of the project was to develop scalable, comprehensive strategies for making the entire group of buildings more energy efficient. Under the current grant regime, the actual strategy selected can be realized cost-effectively; it is now being implemented within the framework of a full-scale renovation partly funded by Wohnfonds Wien. The special feature of this project is that heating, ventilation, etc. are implemented en bloc for all three buildings: Heat is supplied “cross-border,” and ventilation is handled by a central system for the whole group of buildings.

The following renovation measures are now in progress:

  • installing a central transfer station from the district heating grid
  • installing a solar facility to aid in providing hot water
  • installing a central plant for comfort ventilation
  • adapting room layouts to today's needs
  • attic conversion in all three buildings
  • providing barrier-free access to all three buildings
  • organizing the open space across property boundaries.

ROOFJET Wißgrillgasse: Factor-8 renovation with ultra-efficient attic conversion

This building, in Penzing, was put up around 1900; the main building, with its segmented façade, faces onto the street, with a courtyard wing joined via the staircase. This arrangement involves a considerable proportion (32 percent) of freestanding firewalls bordering on various neighboring plots. The goal of renovation was to modernize the existing building in order to economize on resources, and to convert the attic to two stories in an ultra-efficient way.

The comprehensive renovation strategy incorporates numerous scalable elements:

  • renovating the building envelope to a high standard and cutting down on thermal bridges
  • installing different central/decentral convenience ventilation systems
  • CO2-neutral heating arrangements (pellet-fired central heating, with solar collectors integrated into the façade and tied in)
  • installing a stand-alone PV facility for the attic
  • reducing electricity consumption by means of efficient heating and ventilation, plus LED outdoor lighting
  • planting greenery on flat and sloping roofs to improve the microclimate.

Renovating the building in Wißgrillgasse was successfully completed in the spring of 2011. With heating energy demand cut to 27.5 kWh/m2a, the building now meets the standard for ultra-low energy consumption.

Denkmalaktiv: Research for listed buildings that point the way ahead

The research project “denkmalaktiv” is intended to harmonize the aim of conserving listed buildings with technical requirements for energy-efficient renovation. The scope of the project covers identifying and further developing new technologies for renovating historic buildings sustainably, and working out renovation strategies for five typical listed buildings in the center of Graz. Simulation and instrumentation processes were used to analyze the effects of various different renovation measures, and the strategies were further refined as a consequence.

The project team is made up of representatives of the city administration (City of Graz Environmental Department), university and private research organizations (Graz University of Technology, Institute of Thermal Engineering, and Institute for Building Construction, GET Güssing Energy Technologies), and the Graz Energy Agency. The Federal Conservation Agency is also involved in the discussion. Subsequently, these approaches are to be incorporated in specific renovation projects undertaken by the City of Graz; at the implementation stage, scientific supervision will be provided. The initial project phase has already been completed and is providing scalable results. Dialogue between the relevant stakeholders in Graz has begun through workshops and interviews.

In connection with improving the thermal performance of historic buildings, the following technical issues have been dealt with:

  • utilizing capillary active internal insulation systems
  • upgrading box-type windows with respect to thermal and hydric behavior
  • renovation and the fluid dynamics of box-type windows
  • implementing ventilation systems with control facilities
  • thermal wall activation for improving thermal comfort
  • the potential of thermal activation for reducing wall moisture
  • utilizing solar energy in active systems.

The framework for these investigations is focused on five selected reference buildings in Graz (see illustrations above), which have undergone structural, equipment, and architectural analysis. The project team worked out various renovation strategies for each building and assessed them with respect to saving useful energy, end-use energy, primary energy, and CO2 emissions. In addition, the architectural impact with respect to conservation was analyzed in qualitative terms. It turned out that, in all the buildings investigated, it is possible to implement structural and equipment measures that result in significant improvements in energy efficiency while complying with conservation requirements.

International ties

The link to an international group of experts active in the field of thermal renovation runs through the International Energy Agency's Implementing Agreement SHC (Solar Heating and Cooling) TASK 47 (Solar Renovation of Non-Residential Buildings) program. The Institutes of Graz University of Technology participating in “denkmalaktiv I” are project partners in this task, and table the results of their research in this forum.

Vision of zero-emission standard: Renovating the Franciscan Monastery, Graz

The renovation of the Franciscan Monastery in Graz is an impressive example of implementing a sustainable renovation strategy in difficult circumstances. Together with the Franciscan church and the tower, which was originally part of the town wall but is now attached to the church, the Franciscan Monastery forms one of the most prominent groups of buildings in the Old Town. Along with all the technical and economic challenges, a way had to be found to cope with the requirements imposed by the Federal Conservation Agency, the need to conserve the local architectural heritage, and restrictions to protect the UNESCO World Heritage site.

The starting point for renovation was a master plan (Arch. DI Michael Lingenhöle) with a comprehensive strategy for modernizing the entire monastery premises. Together with experts from AEE INTEC, the (utterly committed) monks succeeded in developing a four-stage “energy vision” for the monastery and implementing it, starting in 2010 (Architecture HoG Architekten). Some of the measures carried out were analyzed within the research project “denkmalaktiv I.”

Structural measures

Insulating the monastery‘s pitched roofs contributed significantly to improving energy efficiency; the unheated storage rooms in the attics now function as thermal buffer zones in terms of heat flowing upwards / to the outside. The monastery walls did not need insulating, as thermography revealed only minor heat losses through them. The top floors were thermally insulated with foam glass granulates. Box-type windows replaced the single-glazed corridor windows with insulating glazing inside.

Heating, ventilation and energy strategy

A heating facility keeps the masonry dry and improves the indoor climate. A solar facility with 193 m2 of panel collectors integrated into the roof and 180 m2 of collectors integrated into the façade has been installed; the collectors supply heat for hot water, to warm the walls, and to preheat the well water used in two heat pumps. The collectors were fabricated especially for this project; for the sake of the building's appearance, so-called blind collectors (without an absorber) were fabricated and installed.

The heated water is stored in the basement in three tanks with a capacity of 15,000 liters. As the monastery walls can store a great deal of heat, the inflow temperature is a mere 32° to 33°C. Two heat pumps (rated at 200 kW each, with solar preheating) can deliver any additional energy required for heating and supplying hot water. Finally, the monastery was connected to the district heating system as a backup.

"To achieve thermal efficiency when renovating old buildings, one must pay close attention to the technical aspects of the building in question. If renovation is to result in major savings in energy consumption, and the building‘s architectural value is to be conserved, a whole series of circumspect measures will be needed. Apart from the technical challenge, architecturally inspired solutions are essential; after all, motivation in ecological action derives not only from the functional aim, but also from beauty – from aesthetics!"


SchulRen+: Renovating schools to energy surplus standard

Every year, the central government and the Austrian provinces invest several million Euros in maintaining school buildings. Thus. there is plenty of potential for reducing greenhouse-gas emissions. To date, though, this potential is lying fallow, as no comprehensive strategies involving criteria for energy efficiency are available to the policy makers. With a typical Gründerzeit Viennese school (built in 1898) as a starting point, researchers at the Energy Department in the Austrian Institute of Technology (AIT) have investigated innovative approaches to turning such buildings into net suppliers of energy.

The goal of the technical feasibility study was to marry pioneering energy strategies to structurally and architecturally valid solutions and to identify renovation strategies that can be transferred to similar school buildings. Comprehensive analysis has established that renovating schools to energy surplus standards is feasible from the structural, spatial-functional, and energy points of view. Thermal renovation, coupled with around 400 m2 of PV panels and 30 m2 of solar collectors, results in a negative balance of primary energy over a full year for the building investigated. Outlays on energy could thus be reduced by approx. €50,000 per annum.

To put such model school renovation projects into practice, there is a need for new funding arrangements (such as public-private partnerships, contracting or interacting) and modified grants schemes and/or new financing mechanisms geared to promoting innovation (e.g., in the shape of an energy efficiency fund for public buildings).

“For new types of schools, changes to the room schedule in existing schools are required. Where renovation measures are needed for structural reasons, this is a chance to modernize the buildings comprehensively, including energy and spatial/functional aspects. In this way school buildings can not only contribute actively to climate protection, but also act as key disseminators by setting a good example.


Flagship Project “Gründerzeit mit Zukunft“/ Demonstration projects

e7 Energie Markt Analyse GmbH

Contact: Walter Hüttler

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City of Graz / Umweltamt

Contact: Wolfgang Götzhaber



Grazer Energieagentur

Contact: Gerhard Lang

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Graz University of Technology, Institute of Thermal Engineering

Contact: Thomas Mach

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Franciscan Monastery Graz

Contact: P. Matthias Maier

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AEE INTEC – Institute for Sustainable Technologies

Contact: Armin Knotzer

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AIT Austrian Institute of Technology / Energy Department

Contact: Doris Österreicher

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energy innovation austria presents current Austrian developments and results from research work in the field of forward-looking energy technologies. The content is based on research projects funded by the Austrian Federal Ministry for Transport, Innovation and Technology and the Climate and Energy Fund.