The displacement flow units types QLE and QLF are primarily employed in comfort conditioning. As opposed to the familiar principle of mixed air flow through ceiling or wall diffusers, displacement flow units guarantee low-turbulence air supply. The discharge velocity is very low.

Depending on the degree of activity of the persons in the occupied zone, the supply air can enter the space with a temperature difference of -1K to -6K in relation to the room air. The air spreads out on the floor and is lifted up by convection currents from heat sources (machines, electrical equipment, people, etc.). The fresh air, therefore, finds its own path to the heat source from which the heat load must be removed. With an even distribution of displacement flow diffusers, even large halls (e. g. auditoria, industrial factories) can be air-conditioned without draughts in an economical manner.