AE4-1322
© 2002 Copeland Corporation
Issued 4-2002
Printed in U.S.A.
5
there is no need to move the slide. No solenoid valve
is energized.
The control input can be the air or water temperature at
the evaporator or the suction pressure.
Chart A
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Minimum Capacity
Minimum Capacity
Minimum Capacity
Minimum Capacity
Minimum Capacity
m
m
m
m
m
CR
1
2
3
4
Start/Stop
m
m
l
m
Cap
⇑⇑⇑⇑⇑
m
m
m
l
Cap
⇓⇓⇓⇓⇓
m
m
l
m
Cap
⇔
⇔
⇔
⇔
⇔
m
m
m
m
Cap. 100%
m
m
m
l
Cap. Min.W
m
m
l
m
Chart B
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Control Sequence – Infinite Capacity Control
Minimum Capacity 50%
Minimum Capacity 50%
Minimum Capacity 50%
Minimum Capacity 50%
Minimum Capacity 50%
Cap
⇑⇑⇑⇑⇑
m
m
m
m
m
m
m
m
m
m
l
l
l
l
l
4 Cap.
m
m
m
m
m
l
l
l
l
l
m
m
m
m
m
m
m
m
m
m
Min.50%
Increased cooling demand
Increased cooling demand
Increased cooling demand
Increased cooling demand
Increased cooling demand
If the actual value exceeds the upper set point, the
cooling demand has increased (operating point A in fig.
4). The solenoid valve CR4 is opened for short intervals
till the actual value is within the set control range again
(operating point B). Now the compressor operates with
increased cooling capacity.
Chart C
Control Sequence – 4-Step Capacity Control
Control Sequence – 4-Step Capacity Control
Control Sequence – 4-Step Capacity Control
Control Sequence – 4-Step Capacity Control
Control Sequence – 4-Step Capacity Control
CR
1
2
3
4
Start/Stop
m
m
l
m
Cap 25%
m
m
l
y
Cap 50%
m
l
m
y
Cap 75%
l
m
m
y
Cap. 100%
m
m
m
m
m
Solenoid Coil De-Energized
Solenoid Coil De-Energized
Solenoid Coil De-Energized
Solenoid Coil De-Energized
Solenoid Coil De-Energized
l
Solenoid Coil Energized
Solenoid Coil Energized
Solenoid Coil Energized
Solenoid Coil Energized
Solenoid Coil Energized
y
Solenoid Coil Pulsing (10 secs. on / 10 secs. off)
Solenoid Coil Pulsing (10 secs. on / 10 secs. off)
Solenoid Coil Pulsing (10 secs. on / 10 secs. off)
Solenoid Coil Pulsing (10 secs. on / 10 secs. off)
Solenoid Coil Pulsing (10 secs. on / 10 secs. off)
Decreased cooling demand
Decreased cooling demand
Decreased cooling demand
Decreased cooling demand
Decreased cooling demand
A decreased cooling demand falls below the lower set
point (operating point C). The solenoid valve CR3 now
opens for short intervals till the actual value is within
the set control range again (operating point D). The
compressor operates with decreased cooling capacity.
With the solenoid valves CR3 / CR4, capacity can be
controlled between 100% and nominally 25%. Alterna-
tively valves CR2 / CR4 can be energized; in this case
control will be limited between 100% and nominally
50%.
The limitation to a minimum of approximately 50%
cooling capacity is recommended for the following
application conditions (control with valves CR2 / CR4):
•
In case of operation at high-compression ratios /
condensing temperatures, the main concern is high
discharge temperature.
•
For systems with multiple compressors either used
in split or singlecircuits. Under these conditions
capacity control between 100 and 50%, in combina-
tion with individual compressor on/off cycling,
guarantees highest possible efficiency – without
significant restrictions in the application range. Due
to the usually lowered condensing temperature at
part load conditions, the lead compressor can even
be operated very effectively down to nominal 25% of
cooling capacity (with valves CR3 / CR4)
2.7 4-step capacity control
2.7 4-step capacity control
2.7 4-step capacity control
2.7 4-step capacity control
2.7 4-step capacity control
This type of capacity control is particularly suited to
systems with high inertia – in connection with indirect
cooling, for example. Liquid chillers are typical applica-
tions. Chart C shows the control of the solenoid valves
or the individual capacity steps.
The cycle time of the intermitting valve, CR4, should be
adjusted to about 10 seconds before commissioning.
Even shorter intervals may be necessary, particularly
with systems with high pressure differences. Therefore,
in this case adjustable time relays should be used.
For this type of operation a restriction of minimum
refrigeration capacity to approximately 50% is also
recommended, as with the systems described in
Section 2.6. Control is then effected with the CR4 valve
(intermittent) and with CR1 (75%) and CR2 (50%).
