Danfoss VLT CDS302 Operating Instructions Manual page 112

Parameter Descriptions
25-29 Destage Function
Option:
25-30 Destage Function Time
Range:
10 [0 –
sec. 300
*
sec. ]
6 6
6.14.3 25-4* Staging Settings
Parameters determining conditions for staging/destaging
the compressors.
25-40 Ramp Down Delay
Range:
10 sec. [0 – 120
*
sec. ]
25-41 Ramp Up Delay
Range:
10 [0 –
sec. 120
*
sec.]
112
Operating Instructions VLT
Function:
Disabled, the 25-30 Destage Function Time will not
be activated.
Function:
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.
F VLT pump
Pump
switch-o
F
min
De-stage
timer period
Illustration 6.32
Function:
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.
Function:
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
MG34M302 - VLT
®
CDS302 and CDS303
25-41 Ramp Up Delay
Range:
25-42 Staging Threshold
Range:
90% [0 –
*
100%]
25-43 Destaging Threshold
Range:
50% [0 –
*
100%]
®
is a registered Danfoss trademark/Commercial Compressor
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.
Staging
Speed Speed
Fixed speed pump
(controlled by soft starter)
Lead pump
(controlled by freq. conv.)
t
1 Time
P 25-40
Lead pump starts
to ramp down
Cascade Controller Cascade Controller
calls for another prepares for
pump removing pump
Illustration 6.33
Function:
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
η
LOW
η STAGE % = × 100 %
η
HIGH
to 100%, where n is Motor Speed Low Limit
LOW
and n is Motor Speed High Limit.
HIGH
Illustration 6.34
Function:
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
Destaging
Lead pump
(controlled by freq. conv.)
Fixed speed pump
(controlled by soft starter)
t
2 Time
P 25-41
Lead pump starts
to ramp up