Fan power savings are achieved under low load conditions,
whether system volume reduction is carried out by means of
fan vortex damper, speed control or axial flow controllable
blade pitch control.
Large
central air handling plants facilitate easy free outside air
cooling.
Savings
on initial costs can be effected in air handling/refrigeration
plant and duct sizing by designing with cooling load diversities.
Separate
air handling zone installations are not usually necessary
because individual terminal control action takes care of the
variations in volume and temperature requirements in every
office or room. As a result, initial cost savings are made
in air handling units, ducting and associated equipment.
Simple
system design results in ease of operation, maintenance and
system adjustment.
VAV
Systems are virtually self balancing, thereby almost completely
eliminating costly and time consuming air - quantity setting
procedures.
Through
simple control changes, FLEXIBILITY, to suit partition
changes, is one of the major advantages of the system.
Maintenance
and repair work is made easy as equipment is concentrated
in central plant rooms.
In
Small and medium size systems, direct expansion cooling or
heat pump, may be used, avoiding the greater cost and complications
of water cooling and circulation equipment.
TYPES
OF VAV SYSTEMS
VAV
systems can be divided into two main groups, namely:
Those
that control the volume of supply air at the point of entry
into the room.
Those
that control the volume of supply air further upstream in
the system, such as in a mixing box or duct.
The
first group is by far the more efficient and therefore the
more generally desirable. Modern VARIABLE GEOMETRY room air
entry device design ensures good supply air distribution and
effective room air movement when supplying as little as 30%
of the maximum air-flow.
The alternative form of VAV, utilises an air volume control
device located a considerable distance upstream of the room
air diffusion unit and is therefore not able to take advantage
of the high leaving air velocities to produce good secondary
flows as in the case of the VARIABLE GEOMETRY type.
Under these circumstances, air volume regulation can cause
cold air "dumping" and insufficient room air circulation.
Systems such as these may be useful in internal zones or other
applications which do not exhibit large load variations, such
as shops with relatively constant internal heat gains. An
example of such a diffuser is illustrated above on this page
