25-29 Destage Function
Option:
Function:
Disabled
, the
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
4-11 Motor Speed Low Limit [RPM]
or
4-12 Motor Speed Low Limit [Hz]
(or at
4-13 Motor Speed High Limit [RPM]
or
4-14 Motor
Speed High Limit [Hz]
if
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.
175ZA640.10
F
min
F VLT pump
De-stage
timer period
Pump
switch-off
Illustration 6.32
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
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
25-41 Ramp Up Delay
Range:
Function:
fixed speed compressor to eliminate pressure
surges in the system.
Only to be used if
[1] Soft Starter
is selected in
25-02 Motor Start
.
Speed
Time
Fixed speed pump
(controlled by soft starter)
Lead pump starts
to ramp down
Cascade Controller
calls for another
pump
Cascade Controller
prepares for
removing pump
Lead pump starts
to ramp up
Time
Speed
Lead pump
(controlled by freq. conv.)
Staging
Destaging
Fixed speed pump
(controlled by soft starter)
Lead pump
(controlled by freq. conv.)
t
1
P 25-40
P 25-41
t
2
130BA365.10
Illustration 6.33
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
4-11 Motor Speed
Low Limit [RPM]
or
4-12 Motor Speed Low Limit
[Hz]
to
4-13 Motor Speed High Limit [RPM]
or
4-14 Motor Speed High Limit [Hz]
expressed in
percent.
Staging Threshold must range from
ηSTAGE% =
ηLOW
ηHIGH
× 100 %
to 100%, where n
LOW
is Motor Speed Low Limit
and n
HIGH
is Motor Speed High Limit.
Illustration 6.34
25-43 Destaging Threshold
Range:
Function:
50%
*
[0 –
100%]
When removing a fixed speed compressor, in
order to prevent an undershoot of pressure, the
variable speed compressor ramps up to a higher
speed. When the variable speed compressor
reaches the “Destaging Speed” the fixed speed
compressor is destaged. The Destaging Threshold
Parameter Descriptions
Operating Instructions VLT
®
CDS302 and CDS303
112
MG34M302 - VLT
®
is a registered Danfoss trademark/Commercial Compressor
6
6
