The most reliable building energy performance document in EU is a Display Energy Certificate (DEC). Although mixed of various functions in buildings effects radically on the energy consumption/demand scale, in most cases the buildings on DEC are considered as a single function. This renunciation, in one hand, leads an error on DEC. On the other hand, DEC never displays the effect of changing weather during the year, while for energy management understanding monthly demand is crucial. I am working on energy demand analysing of college buildings taking the above points into account. Any recommendations will be appreciated.