102
Capacity
controller RS8ER302 © Danfoss 2016-02
AK-CH
650
Compressor application 3 – 2 x single step
The controller is able to control a combination of capacity
controlled and multiple single step compressors. The advantage
of this combination is that the unloader valves will be used to fill
in capacity gaps and thereby achieve many capacity steps via few
compressors.
Preconditions for using this compressor application are:
• All compressors are the same size
• The capacity-regulated compressors have the same number of
unload valves (max 3)
• The main step on the capacity-regulated compressors have the
same size
• The main step and the unload valves can be different sizes, i.e.
50%, 25% and 25%.
This compressor combination can be handled in accordance with
the following coupling patterns:
• Sequential
• Cyclical
In general, regarding handling of the capacity-regulated compres-
sors:
Cutin
The capacity-regulated compressors with unloader valves start
before one-step compressors. The capacity controlled compres-
sor will always be fully loaded before cutting-in of subsequent
one-step compressors.
Cutout
The capacity regulated compressor will always be the last to
stop. Handling of the unload valves depends on the setting of
"unloader ctrl mode".
Unloader valves
At cyclical operation unloader valves are used to close capacity
holes from the subsequent one-step compressors.
Anti-cycle timer restrictions
In case a capacity controlled compressor is prevented in start-
ing due to anti-cycle timer restrictions, then the start of any
subsequent one-step compressors is not allowed. The capacity
controlled compressor is started when the timer restriction has
expired.
Cyclical operation - example
The one-step compressors will be cut in and cut out in accord-
ance with the First-In-First-Out (FIFO) principle in order to equalise
operating hours between the compressors.
.
- The capacity controlled compressor is the first to start and the
last to stop.
- Operating hours are equalised between the capacity-regulated
compressors
- The unload valve on the capacity-regulated compressor is used
to fill capacity gaps
- Operating hours are equalised between the one-step compres-
sors 3 and 4.
Compressor application 4 – Only capacity controlled compres-
sors
The controller is capable of controlling capacity-regulated piston
compressors of the same size with up to 3 unload valves.
Preconditions for using this compressor application are:
• All compressors are the same size
• The capacity-regulated compressors have the same number of
unload valves (max 3)
• The main step on the capacity-regulated compressors are the
same size
• The main step and the unload valves can be different sizes, i.e.
50%, 25% and 25%.
This compressor combination can be handled in the following
coupling patterns:
• Sequential
• Cyclical
Cyclical operation - example
The compressors are cut in and cut out in accordance with the
First-In-First-Out (FIFO) principle to equalise operating hours
between compressors.
- For cyclical operation, the compressor with the fewest running
hours starts (C1)
- Only when compressor C1 is completely loaded, should com-
pressor C2 be cut in
- For cut-out, the compressor with the most operating hours
should be unloaded (C2)
- When this compressor is completely unloaded, the second
compressor is unloaded by one step before the main step on the
completely unloaded compressor is cut out.
