Danfoss FC 101 Design Manual page 20

Product Overview
2.6.12 Variable Air Volume
2 2
VAV, or Variable Air Volume systems, 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 utilising 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.
2.6.13 The VLT 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
D1
D3
Illustration 2.11 Variable Air Volume
18
®
VLT
Cooling coil
Heating coil
D2
HVAC Basic Drive FC 101 Design Guide
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 PI controller of the VLT
to eliminate the need for additional controllers.
Pressure
signal
Frequency
converter
Filter
Supply fan
3
Frequency
converter
Return fan
3
MG18C502 - Rev. 2013-09-06
®
HVAC Basic Drive can be used
VAV boxes
Pressure
transmitter
Flow
Flow
T