This standard defines and specifies the performance of standardised energy saving and optimisation functions and routines of Building Automation and Control Systems (BACS) and Technical Building Management (TBM) systems and services. The standard summarises the methodologies to calculate/estimate the energy demand for heating, ventilation, cooling, hot water and lighting of buildings and expresses the results of energy saving and efficiency in buildings by the application of the different BACS energy saving functions. The standard provides a methodology to calculate/estimate energy saving and efficiency in buildings by the application of complex multidiscipline energy optimisation functions realised by integrated BACS and TBM including open data communication networks in buildings.