Control logic
An insufficient oil level can be the result of low
refrigerant velocity in pipes and heat exchangers.
An oil boost sequence consisting of increasing
refrigerant velocity for short periods, at regular
time intervals can improve oil return. Oil boost
function can be done in 2 ways
1. Using internal CDS drive oil boost function
2. Program oil boost function in unit controller
and use optical oil level sensor to trig it.
As oil boost logic needs to increase / decrease
speed, make sure expansion device is fast
enough to maintain liquid flood back within
acceptable limit during those transients.
If the compressor runs below ORM(Oil Return
Management) Min Speed Limit, 28.14) for
more than low speed running time, 28-11, then
function will override the unit controller and
accelerate compressor speed to ORM Boost
Speed, 28.16 for Boost duration 28.13 (28.13
does not include the ramping up time). When
the boost is finished, the compressor speed goes
back to run on reference (speed setpoint) and the
time counter is reset and restarting from zero.
On top of that compressor will boost to ORM
Boost Speed, 28.16 at a fixed time interval as
programmed in parameter 28-12.
Feedback and status message A feedback signal
can be routed back to the unit controller via
programable digital output, relay_2 or Modbus
when an oil boost is initiated.
The unit controller can take actions to keep the
system stabilized during the oil boost period. A
status message “Oil Boost” is also displayed on
the drive LCP during boost.
Oil boost
CDS Drive oil boost
function
28.17 ORM
28.15 ORM
2811-ORM
28.13
d
i
CC-000101
28.17 ORM
28.17 ORM Boost speed
28.15 ORM
28.15 ORM Min speed limit
2811-ORM
2811-ORM Low Speed Running time
d
Decrease ORM time
i
Increase ORM time
28.13
Boost duration 28.13
Drive parameters
Description
value
Default
05-02
Terminal 29 Mode
Output
Input
5-31
Terminal 29 Digital Output
Oil boost active
No operation
5-40.1
Function Relay
Oil boost active
VLT running
16-94 (read)
Ext. Status Word
1000000hex (bit 24)
Pump-down logic
recommendations
Pump down is initiated prior to shutting
down the last compressor on the circuit by
de-energizing a liquid line solenoid valve
or closing electronic expansion valve. When
suction pressure reaches the cut-out pressure,
compressor is stopped, and liquid solenoid valve
or electronic expansion valve remains closed.
•
R
Continuous pump-down: Compressor
restarts automatically when suction pressure
increases up to 4 cycles maximum. A non-return
valve in the discharge line is Mandatory.
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