Specifications

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. 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.

2.7.14 The VLT Solution

While dampers and IGVs work to maintain a constant pressure in the ductwork, a 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 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 can be used to eliminate the need for additional controllers.

Frequency

converter

Frequency

converter

Cooling coil

Heating coil

Filter

Pressure

signal

Supply fan

VAV boxes

Flow

Pressure

transmitter

Return fan

130BB455.10

Illustration 2.17 The VLT Solution

Introduction to VLT® HVAC D... Design Guide

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