Ventilation by displacement is a type of mechanical ventilation that is becoming more popular in Scandinavia. Its physical principle is based on the utilization of density or thermal stratification in order to achieve unidirectional (piston-like flow pattern) flow in the occupied zone. This paper summarizes results from experimental work carried out with regard to this type of ventilation.

Measurements carried out in an office room showed that there are limits to this type of ventilation. There are specific requirements in the design of supply air terminals in order not to exceed comfort criteria with regard to acceptable air velocities. Furthermore, the temperature gradient associated with this type of ventilation puts a restriction on the maximum heat load.

Ventilation by displacement gives rise to larger roomaverage ventilation effectiveness than traditional mixing systems. However, with the flow rates normally supplied to office rooms, the concentration in the breathing zone is the same as with traditional mixing systems.