LTG mixed/displacement ventilation

Air conditioning of rooms means introducing air that has been brought to the required temperature into the zones frequented by people in order to ensure the greatest possible thermal comfort. The performance of conventional room flow configurations is impaired as soon as these frequented zones start to feel uncomfortable. The idea of tangential ventilation, for decades the leading concept in the ventilation field, is to blow air across the ceiling and over the facade in order to circulate the air forcefully around the room. If the cold airstream breaks away from the ceiling too early and descends into the frequented zone, then this leads to the well-known phenomenon of draughts. By contrast, when the room has to be cooled, displacement air ventilation results in cold feet if the outlet temperature is reduced too much in order to increase cooling capacity.

The mixed/displacement air ventilation method developed by LTG and incorporated into VDI 3804 permits high cooling capacities combined with outstanding thermal comfort because it cleverly combines the advantages of both ventilation concepts. Mixed ventilation in the immediate vicinity of the supplied air outlet is followed by a displacement flow into the room to ensure all the benefits of displacement air ventilation.

Thanks to optimised air distribution elements, which are now available in all LTG units, this mixed air ventilation is precisely controlled to ensure a depth of penetration right through to the frequented zone. Systematic flow tests have been performed in order to determine the limitations in the use of the various flow concepts.

The diagram shows the applications of the different flow configurations, which are primarily defined in terms of the thermal comfort they provide. On this basis, it is now possible to implement the ideal flow configuration for the project-specific parameters “cooling capacity” and “supplied air volume flow” using the different LTG air-water systems. We perform engineering services to permit further optimisations designed to fulfil special requirements.


Products with mixed/displacement ventilation: HFVsf, HFG for sill installation and HFG for ceiling installation, HFBsf, VFC, VKB, and FVD.

Flow chart: mixed/displacement ventilation
Areas of use of different flow types
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