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.

2.6.14. 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 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

Pressure

signal

Heating coil

Filter

Supply fan

Flow

Return fan

MG.11.B7.02 - VLT

VAV boxes

Pressure