The energy performances of one residential-business building of the total usable area of 1300m2, located in Belgrade, are analyzed. The one-pipe hot-water radiator system is designed in the building, with splitters and manifolds which are designed for each apartment and each commercial property separately. Cooling system is designed as local system for each apartment and commercial property separately. Heat losses for building are calculated according to DIN 4701. Heat gains are calculated according to ASHRAE transfer function method for load gains, which includes hourly energy simulation techniques for the energy consumption analysis for Belgrade weather data. Annual energy consumption of the building, including heating, cooling, ventilation, and hot water preparation is calculated. The influence of different modes of use of the building to the total annual energy consumption is considered. The temperatures inside the rooms are varied for winter and summer conditions. The different schedules for cooling regime are considered, as a function of the presence of the user, installed lighting and electrical equipment. The influence of the internal shading to the heat gains from solar radiation in summer and also on the annual energy consumption of the building is taken into account. The energy savings that can be achieved using appropriate modes of use of the building is analyzed. Users of the building have a great influence on the building working regime and on rational use of energy.