Displacement AC humidy control

[marcoh]

Am trying to find some design guidelines on designing for space RH control using displacement ventilation systems.

The design parameters are 23ºC / 50% or 8.86g/kg moisture in the occupied zone. For a mixing system the the design is straightforward and the dehumidified supply air needs to offset the moisture gain in the space.

For a displacement system supplying air at 19ºC is it acceptable to supply the air at 8.86g/kg or does it require a lower moisture content? The resultant moisture content in the upper unoccupied zone is not important, and designing to similar principles as a mixing system results in significant plant to dehumidify the air.

 

[GMcD]

You should supply the DV air with slightly less moisture content to allow some pick-up in the space from humidity generating things (humans, and anything else?). So this should not incur much dehumidification if the system is based on 100% outdoor air delivery (climate dependent, of course). The only time you would need to carefully watch the delivery relative humidity of the DV air supply is if you are using chilled beams or chilled ceilings where the warm stratified air might start getting above your dewpoint desires.