Danfoss VLT Refrigeration Drive FC 103 Programming Manual page 133

Parameter Description
20-20 Feedback Function
Option: Function:
NOTICE
If only 2 feedback signals are used, set the
non-used feedback to [0] No Function in
•
Parameter 20-00 Feedback 1
Source.
•
Parameter 20-03 Feedback 2
Source.
•
Parameter 20-06 Feedback 3
Source.
Note that each setpoint reference is the
sum of its respective parameter value
(parameter 20-21 Setpoint 1,
parameter 20-22 Setpoint 2, and
parameter 20-23 Setpoint 3) and any other
references that are enabled (see parameter
group 3-1* References).
NOTICE
Set any unused feedback to [0] No function in
•
Parameter 20-00 Feedback 1 Source.
•
Parameter 20-03 Feedback 2 Source.
•
Parameter 20-06 Feedback 3 Source.
The PID controller uses the feedback resulting from the
function selected in parameter 20-20 Feedback Function to
control the output frequency of the frequency converter.
This feedback can also:
Damper
Cooling/
heating coil
Damper
Damper
Illustration 3.47 Example, Multi-zone, Single Setpoint
MG16H202
Programming Guide
Supply
air fan
Return air fan
Danfoss A/S © 05/2016 All rights reserved.
•
Be shown on the frequency converter's display.
•
Be used to control a frequency converter's analog
output.
•
Be transmitted over various serial communication
protocols.
The frequency converter can be configured to handle
multi-zone applications. 2 different multi-zone applications
are supported
•
Multi-zone, single setpoint
•
Multi-zone, multi-setpoint
Examples 1 and 2 illustrate the difference between the 2
applications:
Example 1 – Multi-zone, single setpoint
A VAV (variable air volume) VLT
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
parameter 20-20 Feedback Function to [3] Minimum, and
entering the desired pressure in parameter 20-21 Setpoint 1.
If any feedback is below the setpoint, the PID controller
increases the fan speed. If all feedbacks are above the
setpoint, the PID controller decreases the compressor
speed.
P P
VAV
Box
P P
VAV
Box
P P
VAV
Box
®
HVAC Drive system must
Zone 1
Zone 2
Zone 3
131
3 3