Dating the time of inexpensive energy, there are HVAC systems with high energy consumption and buildings with insufficient insulation. Since the energy crisis, improvements have been made in different fields. Recognition of dependencies between energy consumers in air-conditioned buildings has led to considerations of integrated energy use today. For this purpose, computer programs have been developed to analyze the following main energy consumers:

• air-conditioning system (air treatment and load compensation)
• lighting system
• heating system (air conditioning not working).

This paper discusses the calculation of annual total energy consumption of the above-mentioned systems in office buildings. Especially, design of fenestration is varied in order to minimize energy consumption. Recommendations are given for window size, insulation of windows and outside walls, shading and orientation, together with optimum use of daylight and passive solar gain. Compared to the figures before the oil price crisis, total energy consumption has been reduced by half and soon will reach approximately a third using available economical technology.