Version 2.02 15.05.2007 Function of VS 3000
16
3.12 Second setpoint - Setpoint increase/decrease
With low-pressure control there is the option of programming a second characteristic that can be activated by
the internal week timer or a digital input of the controller. Polarity of the digital input signal is definable. Setpoint
increase/decrease allows better matching to night and weekend operation.
Setpoint toggle changes the following controller parameters:
- Temperature setpoints
- Neutral zone
- Control constant
- Control times
- Humidity shift
3.13 Refrigeration compressor packs with oil equalizer
Oil level in the compressors differs due to varying suction pressures. So as to achieve equalization of oil level
between the separate compressors, the system is stopped for 2 minutes after one or more compressors has
been operating longer than 3 hours.
At the end of the maximum operating time, fast unload takes place with compressor capacity stages being un-
loaded at the rate of one every 2 seconds. Refrigeration point enabling is disabled when the last capacity stage
is unloaded.
The refrigeration point is re-enabled after the standstill time has expired. The c ompressor capacity stages are
then again loaded step by step. Forced shutdown can be disabled or enabled by the parameter Oil eq. line
(Menu 3-1).
3.14 Capacity-controlled compressors
The VS 3000 Pack Controller can be used to control capacity-controlled compressors having up to three capac-
ity stages (base load plus two capacity stages (bypass valves)). The number of capacity stages is definable. Ca-
pacity-controlled compressors do not have any effect on the control algorithm of the VS 3000. Only the control
sequence is changed.
When the compressors are actuated, the base load of an available compressor is first switched on. The capacity
stages of the c ompressor are then loaded as refrigeration is demanded before the base load stage of the next
compressor can be switched on. Capacity stages are unloaded in the r everse order.
The number of capacity stages actuated for one compressor is taken into account for compressor base load
rotation. The base load stage of a compressor can be controlled by the integral manual switches. When the
base load stage is shut down, the controller also shuts down the associate capacity stages.
When the base load stage of a c ompressor is switched on, the capacity stages of this compressor are loaded
first as refrigeration is demanded.
If both non-capacity controlled and capacity controlled compressors have been defined by parameter, the capac-
ity-controlled compressors are loaded first. This again takes place in the order described above (base load
stage followed by associate capacity stages).
When the full number of capacity-controlled compressors are running at 100%, non-capacity-controlled com-
pressors are loaded as additional refrigeration is demanded. So as to obtain finer staging of capacity, the capac-
ity stages of a capacity-controlled compressor are unloaded when a non-capacity-controlled compressor is
loaded. This means that only the base load stage of the capacity-controlled compressor runs until additional re-
frigeration is demanded, when the capacity stages are again loaded as required.
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