Civil Engineering Reference
In-Depth Information
Fig. 8.12
Under-fl oor air distribution parallel fan-powered VAV
8.13.3
Under-Floor Air Distribution Series Fan-Powered VAV
This system (Fig.
8.13
) is similar to a series fan-powered variable air volume sys-
tem, except that (1) instead of using the duct for air delivery, it uses the under-fl oor
plenum space, (2) there is an additional return-air bypass arrangement which is used
to by-pass return air to upstream of the fan in order to provide suffi cient dehumidi-
fi cation when it is needed, without the need for a reheat coil, and (3) space heating
is produced by an under-fl oor series fan-powered terminal unit that draws air from
the room rather than the ceiling plenum. 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 traditional cooling systems, but also creates higher
occupant comfort by delivering air with lower speed than what is used in traditional
systems, and where it is most effective.
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, terminal unit 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 reheat strip (if it is used for
dehumidifi cation or heating instead of hot water coil). Duct air leakage, heat trans-
fer from ducts connecting air handling unit to the under fl oor plenum, and effi ciency
