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Displacement ventilation engineering guide

SECTION J Engineering Guide Displacement Ventilation Please refer to the Price Engineer ? s HVAC Handbook for more information on Displacement Ventilation Displacement Ventilation Engineering Guide ENGINEERING GUIDE - DISPLACEMENT VENTILATION Introduction Displacement ventilation is an air distribution technology that introduces cool air into a zone at low velocity usually also at a low level Buoyancy forces ensure that this supply air pools near the oor level allowing it to be carried up into the thermal plumes that are formed by heat sources This type of air distribution is e ?ective at delivering fresh air to occupants and removing many of the contaminants associated with heat sources while creating a comfortable environment This chapter focuses on the main design criteria for displacement ventilation systems as well as introduces its common applications The following pages will go further into depth on the speci ?c requirements of schools theaters health care and industrial spaces Overview Air ow in ventilated spaces generally can be classi ?ed by two di ?erent types mixing or dilution ventilation and displacement ventilation Mixing ventilation systems Figure generally supply air in a manner such that the entire room volume is fully mixed The cool supply air exits the outlet at a high velocity inducing room air to provide mixing and temperature equalization Since the entire room is fully mixed temperature variations throughout the space are small while the contaminant concentration is uniform throughout the zone Displacement ventilation systems Figure introduce air into the space at low velocities which causes minimal induction and mixing Displacement outlets may be located almost anywhere within the room but have been traditionally located at or near oor level The system utilizes buoyancy forces in a room generated by heat sources such as people lighting computers electrical equipment etc to remove contaminants and heat from the occupied zone By so doing the air quality in the occupied zone is generally superior to that achieved with mixing ventilation Bene ?ts Flexibility - As load distribution changes within the space a displacement system will be able to compensate For example if the space was designed to have a fairly even load distribution and now has the loads concentrated to one side the system is able to compensate as the buoyant forces drive the supply system and will draw the supply air towards the loads IAQ - Because fresh supply air is pooling at the oor level personal thermal plumes draw fresh air up the body All of the warm and polluted air is extracted at the high return When properly designed there should always be a greater amount of fresh air in the breathing zone when compared to a conventional dilution system leading to higher ventilation e ?ciency Green building rating systems such as the LEED program and Green Globes have credits that are applicable to displacement ventilation systems See the Green Tips for further information Energy Savings - Displacement systems present many potential opportunities for energy savings The lower pressure drop associated with displacement ventilation