Civil Engineering Reference
In-Depth Information
Fig. 8.14
Displacement ventilation CV
8.13.6
Displacement Ventilation VAV
This system (Fig.
8.15
) is similar to a variable air volume system with baseboard
heaters except that (1) instead of above the ceiling ducts the supply air is delivered
via a large sidewall outlet near fl oor and (2) a return-air bypass arrangement is used
to bypass return air to upstream of the fan in order to provide suffi cient dehumidifi -
cation when it is needed and without the need for reheat coil,
Utilizing this system similar to the previous system not only results in saving
energy by delivering air with a higher temperature than what is usually used in tra-
ditional cooling systems, but also creates higher occupant comfort by delivering air
where it is most effective. The terminal unit modulating damper controls the air
entrance to the room based on the need specifi ed by the room temperature sensor.
The sources of energy consumption in this type of systems are the air handling
unit supply fan motor input power, return fan motor input power, electric preheat
strip (if it is used for freeze protection instead of hot water coil) in air handling unit
and electric baseboard reheat unit (if it is used for dehumidifi cation or heating
instead of hot water coil). Duct air leakage, heat transfer from ducts connecting air
handling unit to the variable air volume unit and sidewall diffuser, and effi ciency
loss in water coils are other sources that can indirectly increase the energy con-
sumption of the system. The small energy consumed by low voltage power provided
