The feedback resulting from the function selected in par. 20-20
will be used by the PID controller to control the output frequency of
the adjustable frequency drive. This feedback can also be shown on the adjustable frequency drive’s display, be used to control an adjustable frequency
drive's analog output, and be transmitted over various serial communication protocols.
The adjustable frequency drive 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
to option [3], Minimum, and entering the desired pressure in
. 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
and par. 20-23
Setpoint 3
. By selecting
Multi-setpoint minimum
, [5], in
, the PID controller will increase the speed of the fan if any one of the feedbacks is below its setpoint and decrease the
speed of the fan if all feedbacks are above their individual setpoints.
VLT HVAC Low Harmonic Drive Instruction
Manual
6 How to Program the Low Harmonic Drive
MG.16.A1.22 - VLT
®
is a registered Danfoss trademark
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