Specifications

2.7.12 Application Examples
The next few pages give typical examples of applications
within HVAC.
For further information about a given application, consult
the Danfoss supplier for an application note that gives a
full description of the application.
•
Variable Air Volume: Improving VAV Ventilation
Systems
•
Constant Air Volume: Improving CAV Ventilation
Systems
•
Cooling Tower Fan: Improving Fan Control on
Cooling Towers
•
Condenser Pumps: Improving Condenser Water
Pumpting Systems
•
Primary Pumps: Improving Primary Pumping in
Pri/Sec System
•
Secondary Pumps: Improving Secondary Pumping
in Pri/Sec System
2.7.13 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. Central systems are more efficient
than distributed systems.
The efficiency comes from using larger fans and chillers,
which have higher efficiencies than small motors and
distributed air-cooled chillers. Savings are also realised
from the decreased maintenance requirements.
2.7.14 The VLT Solution
While dampers and IGVs work to maintain a constant
pressure in the ductwork, a frequency converter solution
saves more energy and reduces the complexity of the
installation. Instead of creating an artificial pressure drop
or 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 decrease the pressure and
flow they produce as their speed is reduced. Their power
consumption is 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 more controllers.
Frequency
converter
Frequency
converter
D1
D2
D3
Cooling coil
Heating coil
Filter
Pressure
signal
Supply fan
VAV boxes
Flow
Flow
Pressure
transmitter
Return fan
3
3
T
130BB455.10
Illustration 2.11 Frequency Converters Used in a VAV System
Introduction VLT® HVAC Drive FC 102 Design Guide
24 MG16C102 - Rev. 2013-08-20
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