Displacement ventilation

Displacement ventilation (DV) It is a room air distribution strategy where conditioned outdoor air is supplied at a low velocity from air supply diffusers located near floor level and extracted above the occupied zone, usually at ceiling height.

A typical displacement ventilation system, such as one in an office space, supplies conditioned cold air from an air handling unit (AHU) through a low induction air diffuser. Diffuser types vary by applications. Diffusers can be located against a wall ("wall-mounted"), at the corner of a room ("corner-mounted"), or above the floor but not against a wall ("free-standing"). The cool air accelerates because of the buoyancy force, spreads in a thin layer over the floor, reaching a relatively high velocity before rising due to heat exchange with heat sources (e.g., occupants, computers, lights). Absorbing the heat from heat sources, the cold air becomes warmer and less dense. The density difference between cold air and warm air creates upward convective flows known as thermal plumes. Instead of working as a stand-alone system in interior space, displacement ventilation system can also be coupled with other cooling and heating sources, such as radiant chilled ceilings or baseboard heating.

Displacement ventilation was first applied in an industrial building in Scandinavia in 1978, and has frequently been used in similar applications, as well as office spaces, throughout Scandinavia since that time. By 1989, it was estimated that Displacement ventilation comprised the 50% in industrial applications and 25% in offices within Nordic countries. Applications in the United States have not been as widespread as in Scandinavia. Some research has been done to assess the practicality of this application in U.S. markets due to different typical space designs and application in hot and humid climates, as well as research to assess the potential indoor environmental quality and energy-saving benefits of this strategy in the U.S. and elsewhere.

Displacement ventilation has been applied in many famous building such as the Suvarnabhumi International Airport in Bangkok, Thailand, the NASA Jet Propulsion Laboratory Flight Projects Center building, and the San Francisco International Airport Terminal 2 among other applications.

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