GE AF-600 FP Series Design And Installation Manual page 54

Application Set-Up Examples
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, a 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 seen from the decreased maintenance requirements.
6.3.11 The AF-600 FP Solution
While dampers and IGVs work to maintain a constant pressure in the ductwork, a frequency converter 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 frequency converter 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 HVAC frequency converter can be used to eliminate the need for additional controllers.
Cooling coil
D1
D2
D3
Illustration 6.9 Variable Air Volume System
TM
AF-600 FP Design and Installation Guide
Heating coil
Filter
DET-768b
Pressure
signal
Supply fan
3
Pressure
transmitter
Flow
Return fan
Flow
3
6
VAV boxes
T
51
6