2.6.12. 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.
This greater efficiency is a result of utilizing larger fans and larger chillers, which have much higher
efficiency rates than small motors and distributed air-cooled chillers. Savings are also a result of
decreased maintenance requirements.
2.6.13. The VLT 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 VLT HVAC Drive can be used to eliminate the need
for additional controllers.
Pressure
signal
VAV boxes
Flow
Flow
Cooling coil
Heating coil
D1
D2
D3
Filter
Pressure
transmitter
Supply fan
Return fan
T
3
3
2. Introduction to the VLT HVAC Drive VLT
®
HVAC Drive Design Guide
26
MG.11.B4.22 - VLT
®
is a registered Danfoss trademark.
2
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