Extending the exergy concept to practitioners and policy makers is still a major challenge. Recently the "Canton of Geneva" in Switzerland introduced a new law governing the procedures of attribution of building permits for new or retrofitted city areas. Authorities were asked to define a procedure including the calculation of an exergy indicator to be quantified in each file concerning large projects submitted for acceptance. This paper summarizes the problem definition, a clarification of the limits expected from the exergy indicator as well as the spreadsheet tool and the tables used to facilitate this quantification both for heating and air conditioning. For simplification the overall system was divided into a superstructure formed by four subsystems including the room convector, the plant of the building, a possible district heating and cooling plant and an external power plant. Three temperature ranges were considered for the building distribution networks both in heating and cooling. Ten different technology combinations were considered ranking from the lowest heating exergy efficiency with nuclear electricity and joule heating to the best efficiency with hydroelectricity and District heating electric heat pumps using lake water. (C) 2007 Elsevier Ltd. All rights reserved.