There has long been a concern that evaluating building thermal performance on the basis of energy loads is inappropriate to achieve overall energy efficiency of houses, particularly passive houses, in temperate climates. Passive buildings designed to be free running may achieve better results in an appropriate evaluation system. The main objective of this study is to investigate differences between thermal performances of houses in different operation modes. The paper illustrates a relationship between indicators of building performance in free running and conditioned modes. Simulation is used to compare the predicted performances of conditioned and free running houses, respectively on the basis of annual energy requirements (MJ/m2) and Degree Discomfort Hours (DDH) in temperate climate of Babolsar, Iran. Despite a strong relationship between these two indicators, some significant differences become clear leading to a discussion of the persistent technical problems and issues, which are encountered when attempting to optimize an efficient architectural design. The result of this study persuades the architects to pay more attention to the process of building energy efficient design regarding to the building operation mod. Application of this result in the building labelling system can promote the passive building design which is an important step to achieve objectives of sustainable development
