the frequency converter. This feedback can also be shown on the frequency converter's display, be used to control a frequency converter's analog output,

and be transmitted over various serial communication protocols.

The frequency converter can be configured to handle multi zone applications. Two different multi zone applications are supported:

•

Multi zone, single setpoint

•

Multi zone, multi setpoint

The difference between the two is illustrated by the following examples:

Example 1 – Multi zone, single setpoint

In an office building, a VAV (variable air volume) VLT HVAC Drive system must ensure a minimum pressure at selected VAV boxes. Due to the varying

pressure losses in each duct, the pressure at each VAV box cannot be assumed to be the same. The minimum pressure required is the same for all VAV

boxes. This control method can be set up by setting par. 20-20

par. 20-21

Setpoint 1 . The PID Controller will increase the speed of the fan if any one feedback is below the setpoint and decrease the speed of the fan

if all feedbacks are above the setpoint.

Example 2 – Multi zone, multi setpoint

The previous example can be used to illustrate the use of multi zone, multi setpoint control. If the zones require different pressures for each VAV box,

each setpoint may be specified in par. 20-21

Feedback Function , the PID Controller will increase the speed of the fan if any one of the feedbacks is below its setpoint and decrease the

par. 20-20

speed of the fan if all feedbacks are above their individual setpoints.

114

Feedback 2 Source or par. 20-06 Feedback 3 Source .

Feedback Function will be used by the PID Controller to control the output frequency of

Setpoint 1 , par. 20-22 Setpoint 2 and par. 20-23 Setpoint 3 . By selecting Multi setpoint minimum , [5], in

MG.16.A1.02 - VLT

VLT HVAC Low Harmonic Drive Operating In-

NB!

If only two feedback signals are used, the feedback that is not to be used must