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To achieve European climate neutrality by 2050, it is necessary to rethink the use of energy and resources. Circular economy plays a central role in this task as a third pillar together with decarbonization and increased efficiency.

The Austrian Circular Economy Strategy and the European Circular Economy Action Plan play a vital role with regard to this development: raw materials should be kept in the economic cycle for as long as possible, waste avoided and products made repairable, reusable and recyclable. This is to reduce resource consumption and the environmental impact of industry, but also to lower energy requirements along the entire value chain - from raw material extraction to disposal.

The current issue of “sustainable technologies” deals with applications and innovative approaches that highlight the potential of circular economy for the energy transition. Efficient plastics recycling processes, the recovery of proteins from food production waste streams or innovative material cycles in the construction industry – examples presented in this issue demonstrate that circular economy is not an abstract vision but is already being put into practice.

Is it more important to take measures to stabilize climate change and reduce greenhouse gas emissions or to take measures to strengthen the resilience of society, the ecosystem and infrastructure with regards to the effects that climate change already has? The answer to these questions seems to be simple, because there is no doubt that enormous and rapid efforts are needed in both interrelated fields to avert dramatic damage and high costs to our economy and to the global population.
While a portfolio of measures to reduce greenhouse gases has been in place for decades, measures to prevent or reduce the negative effects of climate change are currently not very widespread and their benefit is still difficult to quantify. For this reason, in the current issue of “sustainable technologies”, we focus on the important and challenging topic of urban heat islands due to climate change and report on promising developments with regards to greening of buildings, development of technologies and digital tools in this field as well as exemplary implementations with regards to the adaption of buildings and cities to the climate change effects.

The need for large-scale heat storage facilities to phase out fossil fuels in the district heating sector is enormous. Based on Euro Heat & Power's forecast of a European district heating demand of 1,780 TWh in 2050 and the assumption that around 5 to 15 percent of the annual heat demand will have to be stored temporarily, this would result in a calculated number of storage facilities of 22,500 to 67,500 with 100,000 m³ of water equivalent each.
The implementation rate has not been able to keep pace with the potential yet. Therefore, international collaboration at IEA level, cooperation within European research projects, national initiatives and simply the need to act regarding climate targets, are giving momentum to the topic. As a result, pilot plants are built in Denmark and Germany, as well as in other European countries. In Austria, several large heat storage facilities are currently being planned, for example the construction of a new type of underground tank storage facility for Fernwärme Wien.
The current issue of the magazine “sustainable technologies” provides an overview of national and international activities, technologies being used, and shows the excellent position Austrian players take in that field. But political commitment will be needed to implement such important future energy infrastructures.

International cooperation has always been a high priority at AEE INTEC. Since the beginnings of our institute, we have looked beyond national borders and developed and implemented sustainable solutions in numerous projects at European level and in cooperation with international organizations such as UNIDO and ADA. These partnerships have taken us from Europe to Asia via Africa to Latin and South America. The scientific exchange that we maintain with these collaborations is always based on communication as equals and joint learning. From this openness and curiosity, we have gained valuable impulses and insights for our own research. In this issue, we share insights into our international activities and reflect on how they enrich our work and our understanding of research in a global environment.

The energy transition and the phasing out of fossil fuels require innovative approaches for the energy supply for building quarters and neighbourhoods. Whether it is district heating and cooling on a low-temperature basis, the collaborative provision of energy flexibility in the form of energy storage systems or the implementation of renewable energy communities, solutions at district level are superior to concepts at individual building level in several respects. Renewable energy sources can be used more efficiently and cost-effectively at neighborhood level, while at the same time having positive aspects in terms of the direct involvement and motivation of the population to invest in energy technologies. In this way, the activation of our settlements and neighborhoods represents an enormous lever for accelerating the implementation of a sustainable energy transition.

The current focus of our magazine “nachhaltige technologien” provides an insight into current energy innovations in districts and the associated learnings from the implementation processes. In addition, the lead article of the current issue deals with the changes in the European Energy Performance of Buildings Directive, such as the replacement of the nearly zero-energy building with the zero-emission building – accompanied by a large number of measures.

“The energy transition to renewable energies cannot be reached without the intensive use of green hydrogen”, this statement can be heard often, and it should be discussed.
Hydrogen as a direct substitute for natural gas could offer several advantages - part of the existing infrastructure can be used, conversion technologies do not need to be changed and the energy supply is secure. But is this the case? Where will the green hydrogen that is needed come from in future? Will Europe shift from fossil dependencies to hydrogen dependencies as it will not be possible to meet the European demand with production capacities located in Europe? What price will Europe have to pay and is hydrogen the most suitable energy source or will there be competitive alternatives like ammonia, methanol, or dimethyl ether?
These are just a few questions raised that the current issue of “nachhaltige technologien” tries to answer on a scientific basis.
In addition to well-known technologies such as electrolysis, new efficient methods for biogas production, the application of methane pyrolysis or highly innovative technologies such as photocatalytic conversion of wastewater into hydrogen or methanol will be developed in future.
In order to successfully meet the challenges of the energy transition within the given timeframe, the use of all renewable energy sources is essential. It will be crucial to use all available technologies reasonably and efficiently. This is the only way Europe is able to become independent of external energy sources and global crises.

However, the topic of serial refurbishment is not entirely new, at least in Austria, as the first pilot projects were already realised in the early 2000s. Unfortunately, this model, which is based on standardisation, digitalisation, and prefabrication, has never progressed beyond pilot status and therefore never reached the intended series production stage. Initiatives from several parts of Europe, such as the Netherlands, Germany, and Estonia, are demonstrating "Serialised Refurbishment 2.0" very successfully in a new attempt. In Germany alone, 50 residential buildings have already been serially refurbished in recent years, 25 are under construction and the pipeline of further projects is well-filled. Around 150 residential buildings currently in preparation impressively demonstrate that the leap from individual pilot refurbishments to serial refurbishment can succeed this time and thus make an important contribution to the rapid resolution of the refurbishment backlog in the building sector that prevails throughout the EU. The potential for serial refurbishment in
Austria and the opportunities for the Austrian construction industry? Due to the building typology and the tradition of timber construction, the potential is generally high but targeted initiatives and a (funding) framework that favours the longer term are needed quickly. This focus on "sustainable technologies" provides insight into current European initiatives for serial refurbishment and reports on the status quo in Austria.

Installation figures for compression heat pumps are steeply going up both nationally and internationally. In Austria, over 60,000 heat pumps were installed in 2022, representing a market growth of 60 percent compared to 2021. Predominantly, compression heat pumps are used for space heating in private residential buildings using outside air as the heat source. Despite the huge potential of applying heat pumps in existing multi-story residential buildings, in industry and commerce, as well as in local and district heating networks, these applications are still virtually nonexistent. The background to this fact is that, on the one hand, specific product developments are needed to cope with operating conditions that are significantly different compared to single family homes, and on the other hand, there is a lack of standards regarding different heat sources and their system integration. It is interesting to note that there are further promising heat pump technologies, such as rotating, thermoacoustic and thermally driven heat pumps suitable for these areas of application.

The present issue of the magazine "nachhaltige technologien" gives insight into pilot projects using compression and thermally driven heat pumps and reports on the state of development of rotating and thermoacoustic heat pumps.

Cities play a special role with regard to a successful transformation of our energy and mobility system. In global terms, our cities are responsible for 78 percent of energy consumption and around 75 percent of CO2 emissions. Due to the high level of energy consumption and the limited availability of land for energy conversion, the transformation of the energy supply is significantly more complex and challenging than in rural areas. Against this background, it is essential that city-specific transformation plans are drawn up, that stakeholders and citizens are involved and that the objectives of a future energy supply are fixed by means of binding urban development concepts. Some Austrian cities as well as numerous other European cities have already established transformation concepts and are guided and supported by national as well as international programs. In Austria, "Climate-Neutral City" and "Pioneer Cities" are examples for such programs, on the European level the program "100 European Climate-Neutral Cities by 2030" is in place.

The focus of the "nachhaltige technologien" issue 02-2023 provides insight into these programs, presents transformation roadmaps of exemplary cities and reports on experiences gained with regard to citizens and stakeholders actively contributing to urban transformation processes.

The collection of data and its use through the application of artificial intelligence has gained momentum with respect to a broad variety of applications and business areas. Many of these applications are generating entirely new opportunities and benefits. In the building sector, for example, the use of data from the planning, construction, and especially the operating phases is able to reduce costs and CO2 emissions, as well as improve the user comfort. To this end, a large number of methods are currently investigated in the area of the "Internet of Things" and are already offered as services on the market. The possibilities range from visualizations using dashboards and Building Information Modeling to control strategies supported by operational data, self-learning, predictive building control and multiple forms of digital building twins.

The present focus of the magazine "sustainable technologies" gives an overview about the status quo of international activities and presents an outlook on future developments.

As part of the Green Deal, the European Commission has set itself the goal of achieving climate neutrality by 2050. Therefore, an important pillar is the transformation of our linear economic system in the direction of a sustainable circular economy. This aims at increasing the value of resources along the entire value chain and at closing material cycles.
There are three basic thrusts in the circular economy: using products for as long as possible, keeping materials in the cycle for as long as possible and, above all, using materials carefully and selectively.
This requires a collective change in thinking and the commitment of various stakeholders and responsible parties from politics, business and research, but also the civilian population.
In this issue of our journal "nachhaltige technologien" you will find a comprehensive overview of different research activities, all of which aim to generate value and close material loops.

The focus of the current issue is on using buildings and building components as energy storages. Generally, the importance of storages in a transformed energy system is beyond any dispute. But which technologies should be used in the basically well-filled portfolio? Do we need energy storage systems that are still at a low level of technological maturity today and will not be available until the next decade despite a high level of research intensity? Or should we focus on storage technologies that are largely available, but whose real implementation is associated with higher economic risks due to their large-scale technical dimension and novelty? The answer to these questions is relatively clear from today's perspective, because all thrusts and technologies in the storage portfolio will be needed in future energy systems. However, the alignment of activities requires corresponding efforts today.
The thermal management of already available building component masses as a flexibility option in buildings, has already arrived on the market with regard to technological maturity. It is highly interesting from an economic point of view and has enormous potential for implementation in new construction and renovation. Reports in the current issue of „nachhaltige technologien“ on ongoing demonstration projects provide an excellent overview of new possibilities for the flexible use of renewable energies in buildings, the suitability of different components and building materials for storing options, the degree of prefabrication and standardization, new types of predictive control concepts, and adapted business and utilization models.

Not only the effects of climate change, but also the current geopolitical and energy policy developments raise the awareness that the phase out of the fossil dependencies with regard to our energy consumption is essential. The heating sector, with around 65 percent fossil supply, is heavily affected and faces enormous challenges in terms of the necessary turnaround. The "Renewable Heat Act", which is supposed to regulate the phase-out of fossil fuels, is overdue and stuck in the division of competencies between the federal and state governments. Lost time, since the currently valid legal framework still allows gas heating systems to be installed even in new buildings. The current implementation status of the law, the framework as well as the envisaged timetable is presented in the lead article of the courrent issue of "nachhaltige technologien".
One of the key challenges of the heat transition is the decarbonization of district heating. Urban district heating in particular is heavily dependent on fossil fuels. Transforming existing centralized systems towards locally available, renewable energy sources goes hand in hand with decentralization and with sector coupling. The resulting increase in system complexity places additional demands on planning, implementation and operation and requires new approaches. The large-scale research project ThermaFLEX has developed new approaches at the interface between research and application and implemented them in 10 demonstrators. It was impressively demonstrated that transformation can also be achieved quickly in heating networks.

Digitalization pervades nearly all areas of social and economic life. The digital development offers companies advantages, for example, to better adapt products to customer needs or to constantly optimize business models. In particular, the supply of energy from volatile, renewable sources will be able to exploit its potential even more in the future with the help of digitalization and thus contribute to opimised flexible energy supply solutions.
This issue of "nachhaltige technologien" gives a comprehensive overview of different new approaches with regard to flexibilization of industrial energy systems. Articles about the development of digital energy twins, that enable real-time mapping of renewable energy supply systems for industrial processe, the creation of a digital waste heat atlas, that provides the geo-referenced potential of waste heat utilization for district heating and the development of a platform to use cloud manufacturing for digital supply chain networks as well as shared use of globally distributed manufacturing facilities are a few highlights.

Current developments with regard to simulation of buildings and their energy requirements and comfort conditions before construction have gained enormous momentum in recent years. Innovative computational models and software solutions enable us to integrate virtual building twins in the building‘s design and operation phase. However, the full potential of building simulation has yet to be fully explored. Building simulation will definitely evolve, but what will be the developments in the coming years? There is research concerning the simulation of the microclimate of cities as well as models using cloud computing, automated BIM simulation workflows, low-cost multifunctional sensors coupled with simulation models, data-driven smart city concepts and developments concerning simulation-based control and regulation for continuous optimization of building operations. In the current issue of „nachhaltige technologien“ we have the pleasure to present some of these exciting developments. One trend can be clearly seen in many of these approaches: future simulation models will definitely coexist with smart technology and IoT sensor technology and the technologies will even converge in future.
In this issue, you will have a look at different innovative simulation methods from the application-oriented point of view - from real-time coupling of simulation and operation using digital building twins to microclimate simulations.

Heat storage systems will play a central role in a sustainably transformed energy system. On the one hand, the demand for heat in Austria currently accounts for about 50 % of the energy demand and, on the other hand, heat can be stored much more cost-effectively than electricity from today's point of view.
Activities in the field of large-scale heat storage have increased nationally and internationally in the last few years. In Austria, the research project gigaTES with 18 international partners from industry and research focused on further development of large-scale heat storage systems. Furthermore, as a result of technological developments at the material, component and design level new exciting implementations are expected.
At the international level, an expert working group was also launched last year under Austrian leadership supported by the International Energy Agency. In addition, there are a number of new large-scale construction projects national and internationally, like the heat storage facility of the Danish Fjernvarme Fyn with a volume of 1.05 million m³.
Read more about large-scale heat storages in the current issue of the magazine "sustainable technologies".

For many years now the importance of introducing energy space planning in communities has been emphasized with regard to the sustainable development of urban and municipal structures. However, little progress has been made concerning the transfer of the findings into practice. Actually, the topic is gaining momentum, not only in Switzerland, where there has been experience in dealing with so-called energy master plans for several years, but also in Austria. In the province of Salzburg, the topic of energyspace planning is fixed in so-called "spatial development concepts (Rämliche Energiekonzepte - REK's)", which are mandatory for municipalities. In Styria, the topic was introduced as a contribution to the local development concept (ÖEK); and in Vienna, the mandatory implementation of energy master plans was already decreed in eight districts in 2020. The new magazine „nachhaltige technologien“ presents success factors for this development in respect of the availability of special digital planning tools as well as the establishment of suitable framework conditions and process flows in public administration.

Digitization influences our society in many ways. In addition to well-known developments in the communications industry, in the financial sector, in industry, in trade or in public administration, the topic of digitization increasingly finds its way into the energy sector. New methods and buzzwords such as "Internet of Energy", "digital energy twins", "data-based regulation", "artificial intelligence and energy", etc. are becoming more and more important. The reasons for this are manifold, but are mostly based on the enormous potential for saving energy and resources, increasing efficiency due to the control of process flows, and increasing the share of renewable energies. The opportunities for automated integration of customers including their habits are proving to be particularly promising and challenging at the same time.
The current issue of the magazine "nachhaltige technologien" presents exemplary and current research activities with a focus on digitalization in the energy sector and their expected impact potential. The lead article deals with the contradictively discussed topic „Digitization and Employment“.

In future one of the big challenges will be to implement climate-friendly energy supply systems in buildings and neighborhoods. The focus for Central Europe still is heating in wintertime, but the energy input for cooling devices during summer is increasing. Although there is a large number of research projects in the energy field, there are still barriers to implement innovative solutions in practice.

In the current issue of the magazine "nachhaltige technologien", innovative demonstration buildings and quarters are presented. Diverse solutions prove that energy efficiency, energy savings and well-being of the inhabitants can be implemented in an affordable manner. Monitoring results confirm the innovative approach and the actually very low energy consumption.

Building component activation, energy management systems, ice storage solutions, digitalization concepts for residents are just a few keywords that will be indispensable in future energy and building technology concepts. The examples provided in the magazine are intended to encourage the successful implementation of proven standard solutions as well as new developments and innovations.

Because of Covid-19, numerous scientists of various disciplines called on politicians to push on integrated measures that would both boost the economy and help protect the climate in the long term. Dr. Fatih Birol, Executive Director of the International Energy Agency (IEA), sees this path as essential and gives recommendations for policymakers.

In the context of security and resilience of the energy supply hybrid renewable energy systems play an important role. In recent years, hybrid solar technologies (PVT) have developed in the shadow of the single technologies, namely photovoltaics and solar thermal energy. Now the technology is established with a collector area of 1.17 million m² installed worldwide by the end of 2019. PVT systems have a much higher efficiency per unit area than comparable single technologies. This makes them particularly interesting for the building sector due to the increasing demand of locally generated renewable energy.

Read more about hybrid solar technologies in the current issue of the magazine "sustainable technologies".

Biobased industries aim to reach ressource efficient production and to foster economic growth and employment especially in agricultural regions. For this purpose cost competitve biorefineries have to be developed using progressive process technologies and energy supply systems for converting biomass to utilisable products as well as to source materials for energy production like methane or hydrogen.
The challenge is to demonstrate innovative technologies and develop business models integrating stakeholders along the whole length of the value chain, e.g. integrate supplyers of biomass used in biorefineries as well as well as consumers using bio-based materials, chemicals and fuels. The implementation of demo biorefineries, proving technologies and business models with regard to bio-based materials and demonstrating cost reduction and performance enhancement, is essential in this connection.

The current issue of the magazine “nachhaltige technologien“ provides some insights in European as well as national Austrian initiatives and research projects showing the relevance of sustainable circular economy.

Most probably the untilization of storage technologies will increase significantly in future because energy suppliers are challenged to reinforce the application of renewable energy sources. As renewables are not available continously but fluctuate, it is essential to use storages for transforming the energy system with regard to sustainability. Another important fact is that heat has a share of about half of a country’s total energy consumption and is stored cheaper than electricity. In Austria 50% of the final energy consumption is heat.

Currently available storage technologies for heat and available implementing strategies for systems are not sufficient to reach the aim of 100% energy supply by the use of renewables. Therefore targeted research, development and demonstration of heat storage technologies is necessary. On the one hand compact thermal energy storages reaching higher energy density than water storages to apply with buildings, industry, mobility and relieving the grids, and on the other hand giga-scale water storages are in the centre of attention.

The current issue of „nachhaltige technologien“ shows the status quo with regard to national and international research dealing with various heat storage technologies and their applicability in different sectors.

There are costs for constructing buildings, but there are also costs with regard to the whole life cycle of a building. Defining the life cycle of a building different periods can be determined: the production of building materials (building products), the construction and utilisation period as well as the disposal period. Currently, if buildings are planned, the construction period is well considered, whereas the utilisation period is considered unsufficiently and the disposal period often is neclected.

According to the European Commission 50% of the produced materials and energy consumption and a third of the water usage account for construction and usage of buildings. Moreover the building sector is responsible for about 30% of waste (construction, usage, renovation and dumping of constructing materials.

Therefore it is very important to consider all these aspects to a much higher extent in future. Requirements for sustainable buildings can be realised as soon as economic, ecologic and health aspects are considered within their interdependency. The current issue of „nachhaltige technologien“ deals with integral planning with regard to building life cycles and addresses innovative and interesting approaches.

Sustainable energy supply systems are based on renewable energy sources. Of course the availability of the space required for producing renewable heat and electricity is essential. Currently diverse ways of utilizing the available land area are competing, and using building surfaces could alleviate such competition. Moreover using building components and building surfaces respectively for energy production, energy storage as well as for energy distribution and supply with fresh air could generate synergies in respect to classical functions of building surfaces like aesthetics, weather and heat protection or noise insulation. Because of such multiple integrated functions, reduction of distribution losses as well as high prefabrication potential considerable economic benefits are expected with regard to the life cycle of new built as well as refurbished multi-storey buildings. In respect to refurbishing the existing building stock prefabricated facades are especially advantageous considering short installation time and little strain on the residents compared to conventional refurbishment procedures. Therefore prefabricated facades have a huge potential to increase the overall rate of refurbishment.

In 2016, approx. 30% of the total final energy demand was needed by the Austrian industry sector. Process heat accounts for three quarters of the industrial energy demand and about half of the heat is used on low and medium temperature level. Only 18% of the energy demand from the industry sector is provided by renewable energy sources. Combining the facts of a high share of heat demand in low and medium temperature range and high energy demand of Austrian industry with a comparatively low share of renewable energies, it becomes clear that the implementation of projects in industry will be a key to achieving the emission targets set by the Austrian government.

Energy for industrial processes could be provided by large-scale solar thermal systems. This is technically feasible and economically reasonable and contributes to achieving the climate targets. This has been proven in recent years by the implementation of "best practice examples" in various industrial sectors and in different parts of the world. Nevertheless, further efforts are needed to establish solar thermal energy as an important option for the energy supply of production facilities. The current issue of our newspaper "nachhaltige technologien" offers an insight into various initiatives and implementations as well as research projects aiming at the further development of solar thermal technology for the industry sector. Through the activities in R&D as well as pilot projects and demo systems presented in the magazine the potential for new applications with regard to solar thermal energy for industry will be addressed.

Testing of new (energy) technologies and (energy) systems with realistic boundary conditions is very relevant for research and development. With demonstration systems it is on the one hand possible to gain insights based on the energy systems themselves but moreover broad demonstration sites that also include users are vital for implementing innovative energy systems. Therefore several initatives have been launched in different countries recently.

In Germany a programme called „Schaufenster intelligente Energie“ was started in 2016. Five model regions with different complementary approaches focusing on regional particularities try to contribute to an overall sustainable energy system that is to be built in the near future.

Almost at the same time Austria started its preparations for the research, technology and innovation initiative „Vorzeigeregion Energie“. After having passed several assets three „Vorzeigeregionen“ started in autumn 2018. The regions deal with different topics: „Green Energy Lab“ trys to boost promising energy technologies, demonstrate them and bring them to the market, „New Energies for Industry“ focuses on energy transition for industry and the third „Vorzeigeregion“ puts its emphasis on power based on hydrogen and synthetic gas. More than 200 partner institutions and companies cooperate within this Austrian research and demonstration initiative. The allocated budget is planned to be more than 400 million euros.

The current issue of „nachhaltige technologien“ gives an overview in regard to the German programme „Schaufenster intelligente Energie“ and allows a deeper insight into the Austrian initiative „Vorzeigeregionen Energie“.

The increasing share of renewable energy sources feeding in electricity and heating networks will require a change from demand based energy production to production based energy consumption. This is due to the short-term predictable energy based on wind and solar (PV as well as solar thermal) that is not open to influence, but that could be used more efficiently. That will release pressure from the net and necessary storage facilities. Energy consumption of buildings and building ensembles aligned with future energy production based on renewable energy sources will play a vital role in future.

The possibility to store heat via components of buildings (for example through thermal component activation), the number and size of hot water storages and batteries, the number and equipment of electrical compliances and consumers such as heat pumps, the applied control systems and so on define the building‘s potential of energy flexibility. In future a special focus in regard to heat storage and shift of load peaks of buildings should be on activating of building components. The thermal activated massive ceiling or wall can be additionally used for heating and cooling purposes besides its storage function.

The current issue of „nachhaltige technologien“ tries to characterize sustainable options of energy flexibility for buildings and shows the potential and strategies for implementation.

Water is essential for the energy and food sector. The access to energy, energy security and the environmental impact are influenced by the disposability of water. Fossil fuels need water for extraction, transport and processing. Thermal power plants (based on nuclear, fossil fuels, biomass, concentrating solar power) use water for cooling purposes and for hydroelectric plants resilient river currents are crucial. Similarly, production of bio fuels and bio plastics require water for the production processes.

Energy is important for accessing clean drinking water, for watering in agriculture and waste water treatment: pumping of ground and surface water, treatment and transport of water to the end-users as well as cleaning of wastewater in order to recycle it.

Currently water, food and energy systems are dependent but do not interact actively. In Austria national regulations for energy production and distribution exist whereas issues concerning water are regulated on community level. Industrial agriculture and food processing is ruled by companies and multicorporate enterprises. The analysis of the nexus between energy, food and water therefore tries to address these complex and critical subjects in a holistic and systemic way.

Lately, progress in research and analysis led to innovative technologies and integrated approach concerning the above addressed subjects. In the current issue of the magazine “nachhaltige technologien” examples for these the discussed questions are given.

Considering the overall heating demand in Austria the share of district heating accounts for 25 % and about triplecated since 1990. Nevertheless the development over the last years was less fast than before in respect to sold heat as well as newly installed lines (increasing from 4 900 km in the year 2013 to about 5 400 km in 2016). The reason for this mainly lies in the fact that in the meantime many of the dense city centers and quartiers already are supplied with district heating networks. Moreover the heating demand decreases due to better insulated building standards for newly built houses as well as renovated buildings. Therefore the energy demand per meter of constructed line decreases. This leads to an increase in specific heating losses and thus changes the framework conditions of heating networks in respect to economic feasibility, tariffs and expansion strategies. Classical district heating systems with high temperature levels therefore face limitations.

New district heating network strategies with adapted temperature levels as well as spread production and storage structures with smart control algorithms show completely new possibilities for increasing construction of district heating networks as well as integrating renewables. Recently some projects based on „anergy networks“ and „cold district heating networks“ respectively have been developed. First experiences are available showing the big potential of such networks. Heating networks with low temperature levels and networks using the return flow increasingly get interesting for suppliers. On the one hand the complexity of these systems increases due to new network designs, decentralisation, coupling of energy sectors and new control systems. On the other hand new systems have to be operated in an economically feasible way to be competitive. Both aspects require new simulation and modelling tools that are presented in the new issue of „nachhaltige technologien“.

It is well known that besides technological challenges suitable financing instruments are crucial for financing energy efficiency measures and renewable energy technologies in the industrial sector. Along with subsidies provided by governmental institutions the interest of the private finance sector should be attracted more and more by structuring the market and taking measures for minimizing risks. Investors are increasingly willing to invest their money in sustainable energy projects but the projects have to be processed in an interesting way to attract attention compared to other possible investments. In this connection the risk has to be minimized for investors and an adequate return rate is expected.

Various international studies address the grand need of financing of projects in the field of energy efficiency and renewable energy. In the light of existing financial boundary conditions of the industry sector like long payback periods, illiquid assets and regulatory dependencies, organizing the relationship between governmental bodies and private investors will be crucial for bringing appropriate financing models to the market.

The current issue of “nachhaltige technologien” highlights different examples of possible financing models for buildings as well as for the industrial sector, shows advantages, disadvantages and challenges in establishing the models in the finance sector and describes “best practice examples” of successfully financed projects.

Renewable energies are going to dominate our future energy supply systems and solar thermal energy is an important factor in this field. Large scale solar thermal projects in the pipeline (e.g. BigSolarGraz) and numerous studies carried out by namable institutes illustrate the huge potential.

Besides large scale projects for urban societies there exists a considerable number of different solar thermal applications that are very competitive in terms of primary energy input and economics as well as socioeconomic factors like access to energy, security of energy supply, load relief in respect of electricity grid infrastructures, job creation and so on.

The field of applications stretches from the meanwhile classical hot water preparation to large solar thermal heat/cold supply systems in industry and service buildings as well as systems feeding into the district heating system. There are some new applications in niche markets such as solar drying systems, hybrid systems (PVT) and concentrating solar systems with immense market potential.

In the actual issue of “nachhaltige technologien” we would like to report about promising applications and markets as well as address the activities of export-oriented companies.

New buildings should be built in such a way that they are still energetically and ecologically feasible in 2050. Furthermore experts have to check the building stock in regard to the necessity of high-quality renovation or complete reconstruction. The setup of façades in respect to design layout and construction play a major role in high-quality renovation processes. Furthermore the energy and CO2 emissions saving potential of facades and windows of the building stock is enormous. The current issue of “nachhaltige technologien” deals with this interesting issue.

On the one hand sustainable façade systems are described in different fields of application and on the other hand possibilities of creating additional benefit via façade systems are shown. Multifunctional façade elements that are being developed will reveal their economic advantages compared to conventional wall insulation systems.

Concerning research and development activities in this sector Austria could take a lead role in Europe.

Cities grow worldwide. Considering the last ten years, Austrian regional capitals for example had a population growth rate of about 7.4 % compared to rural areas with a growth rate of 4.3 %. This means a shift of population from the rural areas to the cities and their banlieues. According to this development greenhouse gas emissions caused by urban population increases, too, counting already for 70 % of the worldwide induced greenhouse gases. Therefore activities of city governments in regard to energy efficiency, the deployment of renewable energy sources and sustainable mobility concepts are crucial, even though the achievements currently are not at all sufficient. However, a couple of years ago several city governments decided to develop binding strategies for “smart city” and “low carbon economy” concepts. Beside to successful demonstration projects realized, these city governments (in Austria especially the city governments of Vienna, Salzburg and Graz) developed new tools in respect of urban planning. Novel numerical methods for simulation of complex urban energy system have been developed in cooperation with research institutions.

In the current issue of “nachhaltige technologien” we would like to illustrate these developments.

Resources consumption add up to around 68 billion tons of materials per year, meaning a consumption ten times higher globally than in 1902. Driven by this fact and a number of challenges such as climate change and expanding populations, the development of a so-called "bioeconomy", which drives closing the loop of nutrients like nitrogen, phosphorus and potassium as well as raw materials, is becoming increasingly important.

In this context, the European Commission drafted an ambitious strategy for recycling management at the end of 2015, in which the waste of each economic sector plays an important role. A residue-based bio-economy will contribute to environmental sustainability and it will provide investment opportunities with respect to waste industry markets.

The resources of industrial and municipal wastewater, including digestate from biogas and sewage sludge, are substantial and could drive a long-term strategic paradigm shift towards a bio-based economy. Due to the depletion of non-renewable mineral resources (e.g. phosphorus) and the increase in production costs (e.g. nitrogen fertilizers), the focus of research and development has shifted from disposal and treatment to the recovery of resources.

Technologies such as membrane distillation, to which the current issue of "nachhaltige technologien" is dedicated, are currently of interest for further development. The various examples in the articles show the diversity of the technology, but also demonstrate what challenges need to be solved.

Twenty years after AEE INTEC started publishing the magazine „erneuerbare energie” the magazine was relaunched and adapted to the clearly extended research topics AEE INTEC works on. Therefore the magazine changed its name, contents and structure and it was given a modern layout.

It is not only that the new magazine is now called “nachhaltige technologien”, but it should with its new appearance and structure better attract the quite heterogenous readers.


Recognized experts are going to be invited to write a lead article about energy relevant, environmental or resources-oriented topics that connect the technological research & development themes represented in the magazine to their socio-political context.
The articles reflecting technological developments and presenting project results are going to be more compact than in the past, but readers interested in details will find links to literature and project reports for each article.

Last but not least persons working on technological tasks are going to be introduced to the readers in order to put flesh on the projects.