The IEA Annex 64 focusing on low-ex communities aims at the improvement of energy conversion chains on a community scale, using exergy analysis as the primary evaluation mode. Within this Annex the participants discuss important aspects and available methods for energy and exergy assessment as well as the added value of aiming for low exergy (LowEx) communities. The reason to exploit the exergy approach is that it provides critical insight into how the maximum potential of energy resources can be used, resulting in a reduced need for high quality energy sources. This insight cannot be obtained with energy analysis. However, other aspects play a role when designing an optimal energy system, such as costs or CO2 emissions. There can be reasons that justify exergy destruction. To address these issues the working definition for the annex is that “a LowEx community is a community for which the energy system is designed in such a way that exergy destruction is minimized, or that all exergy destruction is justified by other reasons (e.g. economic / social, other sustainability reasons)”. This paper gives more background on the definition and presents a general overview of exergy analysis of energy systems in the built environment. Different approaches and opinions are discussed, including how these affect the results. The aim is to create a common ground for consideration low exergy systems at the community scale by setting clear precedents for defining evaluation methods, system boundaries, and input classification.@en