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VLT
®
HVAC Drive Programming Guide
NOTE!
Any unused feedback must be set to "No function" in its Feedback Source parameter: par.20-00
2 Source
or par.20-06
The feedback resulting from the function selected in par.20-20
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
Setpoint 1
20-21
. 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
20-20
, 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.
NOTE!
If only two feedback signals are used, the feedback that is not to be used must
be set to
Source
be the sum of its respective parameter value (par.20-21
Setpoint 2
20-22
enabled (see par. group 3-1*).
Feedback 3 Source
.
Feedback Function
Feedback Function
Setpoint 1
Setpoint 2
, par.20-22
MG.11.C6.22 - VLT
®
is a registered Danfoss trademark
No Function
Feedback 1 Source
in par.20-00
Feedback 3 Source
or par.20-06
. Note that each setpoint reference will
Setpoint 3
and par.20-23
) and any other references that are
Feedback 1 Source
will be used by the PID controller to control the output frequency of
to option [3], Minimum, and entering the desired pressure in par.
Setpoint 3
and par.20-23
. By selecting
3 Parameter Description
Feedback 2
, par.20-03
Setpoint 1
, par.
, par.20-03
Feedback
Multi-setpoint minimum
, [5], in par.
3
3-175
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