6.3.10 Variable Air Volume
VAV or Variable Air Volume systems, are used to control
both the ventilation and temperature to satisfy the
requirements of a building. Central VAV systems are
considered to be the most energy efficient method to air
condition buildings. By designing central systems instead
of distributed systems, greater efficiency can be obtained.
The efficiency comes from utilizing larger fans and larger
chillers which have much higher efficiencies than small
motors and distributed air-cooled chillers. Savings are also
a result of decreased maintenance requirements.
6.3.11 The AF-600 FP Solution
While dampers and IGVs work to maintain a constant
pressure in the ductwork, an adjustable frequency drive
solution saves much more energy and reduces the
complexity of the installation. Instead of creating an
artificial pressure drop or causing a decrease in fan
efficiency, the adjustable frequency drive decreases the
speed of the fan to provide the flow and pressure required
by the system.
Centrifugal devices such as fans behave according to the
centrifugal laws. This means the fans decrease the pressure
and flow they produce as their speed is reduced. Their
power consumption is thereby significantly reduced.
The return fan is frequently controlled to maintain a fixed
difference in airflow between the supply and return. The
advanced PID controller of the adjustable frequency drive
can be used to eliminate the need for additional
controllers.
Pressure
signal
VAV boxes
Fl ow
Fl ow
Cooling coil
Heating coil
D1
D2
D3
Fi l t er
Pressure
transmitter
Sup p ly f an
Ret u r n f an
T
3
3
vav2.10
Figure 6.9
Application Set-up Examples AF-600 FP Design and Installation Guide
6-10 DET-768A
6
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