Energy Efficient HVAC System and Building Design presents energy simulation case studies of office buildings located in France. It takes into account the energy consumption of HVAC-system. Two different kinds of buildings have been used. Reference building has external structures of a typical new building in Paris today. In advanced building external walls and windows have lower U-value and improved tightness. Windows have also better shading coefficient and external overhang of 500 mm for solar shading. Different kind of HVAC-system components have been simulated both in reference and advanced building in order to find the lowest possible energy consumption. Result shows that with right HVAC-system and building design can reduce energy consumption 75 %.