Traditionally air has been supplied from the ceiling to the occupants below opposing the buoyancy effects due to heat convected from people, lights and machines. There has also been concern that if air supply outlets are installed at low level near people the chances of draughts and noise are high. The development of swirl air diffusers in Sweden and Germany overcomes these problems and allows a wider consideration of air distribution systems when designing buildings. This also offers flexibility in planning the distribution of electrical systems and piped services. Fresh air is needed at head level if ventilation is to be effective. In high spaces which are densely occupied this is more readily achieved with an upward system.