25-29 Destage Function
Option:
Function:
[0]
*
Disabled
[1]
Enabled The Destage Function ensures that the lowest
numbers of compressors are running to save
energy. If the Destage Function is set to
[0]
Disabled
, the
parameter 25-30 Destage Function
Time
will not be activated.
25-30 Destage Function Time
Range:
Function:
10
sec.
*
[0 –
300
sec. ]
The Destage Function Timer is programmable to
avoid frequent staging/destaging of the fixed
speed compressors. The Destage Function Time
starts when the adjustable speed compressor is
running at
parameter 4-11 Motor Speed Low Limit
[RPM]
or
parameter 4-12 Motor Speed Low Limit
[Hz]
(or at
parameter 4-13 Motor Speed High Limit
[RPM]
or
parameter 4-14 Motor Speed High Limit
[Hz]
if
parameter 7-30 Process PID Normal/ Inverse
Control
is programmed to Inverse), with one or
more fixed speed compressors in operation and
system requirements satisfied. In this situation,
the adjustable speed compressor contributes
little to the system. When the programmed
value of the timer expires, a stage is removed.
175ZA640.11
(4-12)
(27-27)
F
min
F VLT pump
De-stage
timer period
Pump
switch-off
Figure 6.31 Destage Function Time
6.14.3 25-4* Staging Settings
Parameters determining conditions for staging/destaging
the compressors.
25-40 Ramp Down Delay
Range:
Function:
10
sec.
*
[0 –
120
sec. ]
When adding a fixed speed compressor
controlled by a soft starter, it is possible to
delay the ramp down of the lead compressor
until a preset time after the start of the fixed
speed compressor to eliminate pressure surges
in the system.
Only to be used if
[1] Soft Starter
is selected in
parameter 25-02 Motor Start
.
25-41 Ramp Up Delay
Range:
Function:
10
sec.
*
[0 –
120
sec.]
When removing a fixed speed compressor
controlled by a soft starter, it is possible to
delay the ramp up of the lead compressor until
a preset time after the stopping of the fixed
speed compressor to eliminate pressure surges
in the system.
Only to be used if
[1] Soft Starter
is selected in
parameter 25-02 Motor Start
.
Figure 6.32 Ramp-up Delay
25-42 Staging Threshold
Range:
Function:
90%
*
[0 –
100%]
When adding a fixed speed compressor, in order
to prevent an overshoot of pressure, the variable
speed compressor ramps down to a lower
speed. When the variable speed compressor
reaches the “Staging Speed” the fixed speed
compressor is staged on. The Staging Threshold
is used to calculate the speed of the variable
speed compressor when the “cut-in point” of the
fixed speed compressor occurs. The calculation
of the Staging Threshold is the ratio of
parameter 4-11 Motor Speed Low Limit [RPM]
or
parameter 4-12 Motor Speed Low Limit [Hz]
to
parameter 4-13 Motor Speed High Limit [RPM]
or
parameter 4-14 Motor Speed High Limit [Hz]
expressed in percent.
Staging Threshold must range from
η
STAGE %
=
η
LOW
η
HIGH
× 100 %
to 100%, where n
LOW
is Motor Speed Low Limit
and n
HIGH
is Motor Speed High Limit.
Figure 6.33 Staging Threshold
Parameter Descriptions
VLT
®
Compressor Drives CDS 302/CDS 303
116
Danfoss A/S © Rev. 2013-07-03 All rights reserved.
MG34M422
6
6
Summary of Contents for VLT CDS 303
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