ECBCS Annex 49
Low Exergy Systems for High-Performance
Buildings and Communities

Now available

Summary Report: "Exergy Assessment Guidebook for the Built Environment“

the annex 49 project • objectivesstructureoutcomedissemination


The exergy content required to satisfy the demands for the heating and cooling of buildings is very low, since a room temperature level of about 20°C is very close to ambient conditions. Nevertheless, high quality energy sources like fossil fuels are commonly used to satisfy these small demands

for exergy. From an economical point of view, exergy should mainly be used in industry to allow for the production of high quality products.

The new approach is not necessarily focused on a further reduction of the energy flow through a building’s envelope: when the demands for heating and cooling have already been minimised, the low-exergy approach aims at satisfying the remaining thermal energy demand using only low quality energy.
Annex 49 aims at improving, both on a community and building level, the design of energy use strategies which account for the different qualities of energy sources, from generation and distribution to consumption within in the built environment.

Annex 49 is based on an integral approach which includes the analysis and optimisation of the exergy demand in the heating and cooling systems as well as in other processes where energy/exergy is used within the building stock.

It is known that the total energy use caused by buildings accounts for more than one third of the world’s primary energy demand. There is, however, a substantial saving potential in the building stock. The implementation of exergy analyses paves the way for new opportunities to increase the overall efficiency of the energy chain.

The method of exergy analyses has been found to provide the most correct and insightful assessment of the thermodynamic features of any process and offers a clear, quantitative indication of both the irreversibilities and the degree of matching between the resources used and the end-use energy flows.