There is an obvious and indisputable need for an increase in the efficiency of energy utilisation in buildings and in the energy supply system within communities. Heating, cooling and lighting appliances in buildings account for more than one third of the world's primary energy demand. In turn, building stock is a major contributor to energy-related environmental problems and CO2 emissions. There are great potentials to be obtained through a more efficient supply of energy and rational use of energy in buildings. An optimisation of the exergy flows in buildings and related supply structures, similar to other thermodynamic systems such as power stations, can help in identifying the potential of increasing efficiency in energy utilisation. Through analyses, it can be shown that calculations based on the energy conservation and primary energy concept alone are inadequate for gaining a full understanding of all important aspects of energy utilisation processes. The high potential for a further increase in the efficiency of; for example, boilers, cannot be quantified exclusively by performing energy analyses-the energy efficiency is close to 100%; however, this potential can be demonstrated by using an exergy analysis, whereby the exergy efficiency of a common gas boiler is about 8%. It is necessary to work out new and more efficient ways to supply energy to satisfy the demand for energy services. This paper outlines the international co-operative work in the general framework of the International Energy Agency (IEA), the ECBCS Annex 49 "Low Exergy Systems for High Performance Buildings and Communities" [Annex 49, Energy Conservation in Buildings and Community Systems-Low Exergy Systems for High Performance Buildings and Communities, homepage: http://www.annex49.com, 2007]. (C) 2008 Elsevier B.V. All rights reserved.