Danfoss VLT HVAC Drive FC 102 Instruction Manual page 105

How to Program
Examples 1 and 2 illustrate the difference between the
two:
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
FC 102
Damper
Cooling/
heating coil
Damper
Damper
Figure 6.17 Example, Multi-zone, Single Setpoint
Example 2 – Multi-zone, multi-setpoint
The previous example illustrates the use of multi-zone,
multi-setpoint control. If the zones require different
pressures for each VAV box, each setpoint may be specified
in parameter 20-21 Setpoint 1, parameter 20-22 Setpoint 2
and parameter 20-23 Setpoint 3. By selecting [5] Multi-
setpoint minimum in parameter 20-20 Feedback Function,
the PID controller increases the fan speed if any one of the
feedbacks is below its setpoint. If all feedbacks are above
their individual setpoints, the PID controller decreases the
fan speed.
MG11F522
Instruction Manual
®
Supply
air fan
Return air fan
Danfoss A/S © 08/2014 All rights reserved.
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 fan speed.
P P
VAV
Box
P P
VAV
Box
P P
VAV
Box
20-21 Setpoint 1
Range:
0 [-999999.999 -
ProcessCtrlUnit 999999.999
*
ProcessCtrlUnit]
Zone 1
Zone 2
Zone 3
Function:
Setpoint 1 is used in closed-
loop mode to enter a setpoint
reference that is used by the
adjustable frequency drive's
PID controller. See the
description of
parameter 20-20 Feedback
Function.
NOTICE!
The setpoint reference
entered here is added to
any other references that
are enabled (see
parameter group 3-1*
References).
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