IEA ES Annex 49: Low Exergy Systems for High-Performance Buildings and Communities

The objective of Annex 49 is the development of approaches for reducing the exergy demand of buildings, so as to reduce the CO2 emissions of the building stock and support structures for sustainable and reliable energy systems in the building sector. To achieve the objectives of Annex 49, the following activities have been carried out:

  • Application of exergy analysis and providing tools, guidelines, best-practice examples and background information for planners and decision makers in the fields of construction, energy and politics
  • Support of cost-efficient low-energy/exergy measures for renovation and new building taking into account both the residential and the service sector
  • Promotion of exergy-related performance analysis of buildings, particularly from the perspectives of communities / regions

Short Description




In recent years, the international scientific community started to discuss more and more the integration of the exergy concept into energy economic approaches. This is expected to lead to a better understanding of the quality of energy flows. This report has been written in the frame of Annex 49 of the Implementing Agreement ECBCS (Energy Conservation in Buildings and Community Systems Programme) and discusses concepts and methods for reducing the exergy consumption in buildings, communities and regions.

The core content of this project has been the application and dissemination of the exergy concept in the Austrian energy economic community, in particular regarding the space heating and hot water sector. The targets of the project were the dissemination of the exergy concept in Austria, the integration of exergetic analysis in exergy economic scenarios and analyses regarding the cost efficiency of low-ex systems. All these activities were strongly supported by an intensive national and international networking and cooperation within the Annex 49 consortium.

The economic analyses of the systems were based on a profound collection and preparation of corresponding techno-economic data, including a detailed international comparison. For the integration of exergetic analyses in energy economic scenarios we collected and prepared data of existing scenarios and evaluated them regarding the resulting exergetic efficiencies. Moreover, we identified best-practice examples in Austria. Last but not least, we carried out a process of discussion, networking and dissemination.

The energy economic analysis led to the results that there is a clear trade-off between capital input and the exergy content of applied energy carriers. Low-ex systems require substantial investments for making use of low-ex ressources. The results of three scenarios considered show a substantial reduction of the exergy consumption in the Austrian space heating sector in the next decades until 2050. This holds in particular, if corresponding ambitious energy efficiency measures are taken. The analysis of best-practice examples show that up to now the exergy concept concept is not widely applied and no harmonised evaluation takes place under an exergetic point of view.

The key conclusion of this report is, that the use of suitable energy carriers for each application (i.e. regarding the required exergy level) can lead to a significant increase of the exergetic efficiency. This is correlated with a reduction of exergy and energy consumption as well as the related greenhouse gas emissions.

Contact Address

Dr. Lukas Kranzl 
Technische Universität Wien, 
Energy Economics Group (EEG),
Institut für Elektrische Anlagen und Energiewirtschaft,
Gusshausstrasse 25-29/373-2
1040 Wien
Tel.: +43 (1) 58801-37351