3.0 Capacity Control
18
3.1 Suction Cut-Off Capacity Control
Carlyle’s compressor suction cut-off capacity control sys-
tem has been approved for R-502, R-404A, and R-507
applications down to -40°F (-40°C) suction and for
R-12, R-134a, R-407C, and R-22 medium and high
temperature applications, but the system designer must
carefully consider certain system design criteria when
applying this new feature.
3.2 Design for Proper Oil Return to
Compressor
When the 06D/E compressors are unloaded, the com-
pressor and system capacity are reduced by 1/3, 1/2, or
2/3 of full load capacity. These capacity reductions result
in the same large percent reduction in refrigerant flow
rates through the system piping. Oil that is entrained and
carried with refrigerant requires a certain gas velocity to
properly return it back to the compressor and as this
refrigerant flow drops, this may not be possible. This is
especially true of the sizing of the suction line where oil
return is most critical.
All system piping, but especially the suction line, must
consider both full load and part load capacities and
refrigerant velocities when being sized. For complete
details of good system piping practices, the Carrier
System Design Manual (Part 3 - Piping Design) or the
ASHRAE Manual (Systems Volume) is recommended.
Unloading can decrease refrigerant velocities especially
in the compressor and related piping. To help ensure
excessive oil does not accumulate it is recommended to
use a compressor control strategy that loads up a com-
pressor for 60 seconds after 2 hours of continuous
unloaded operation.
To protect the compressor against possible oil return
problems, all 06D and 06E refrigeration duty compres-
sors applied with capacity control must utilize oil safety
switch protection. This requirement may be waived by
Carlyle Application Engineering for certain high tempera-
ture, single compressor circuit applications (contact
Carlyle Application Engineering for approval).
3.3 Capacity Control Application Ranges
Low Temperature R-502, R-404A, and R-507
Application: -40°F to 0°F (-40°C to -18°C)
Saturated Suction Temperatures.
Condensing temperature limits:
For all 4-cylinder 06D and 06E compressors - See
Figure 10. All 6-cylinder 06D and 06E compressors can
be unloaded at all condensing temperatures below
120°F (49°C) with 1 bank of capacity control. Do not
unload more than 1 bank on 6-cylinder 06D or 06E
compressors in this low temperature application.
Note: In low temperature booster applications see differ-
ential pressure limits (DP) (Table 4, Page 20) for mini-
mum condensing pressures required to load up.
For low temperature R-22 applications:
Unloaded operation is limited to the 0°F (-17.8°C) to
-25°F (-31.7°C) saturated section temperature range
and saturated condensing must be below 120°F (49°C).
The use of unloaders is limited to 1 bank on all the 4 or
6 cylinder 06DR or 06ER models.
Medium Temperature R-12, R-134a, R-502, and
R-507 Application: 0°F to 40°F (-18°C to 4°C)
Saturated Suction Temperatures.
Unloading application limits at saturated condensing
temperatures below 130°F (54°C): Can unload 1 bank
on any 4-cylinder 06D or 06E compressor. Can unload 1
or 2 banks on any 6-cylinder 06D or 06E compressor.
Note: With R-134a or R-12 see DP limits (Table 4, Page
20) for loading requirements.
Medium Temperature R-22 Applications: 0°F to
25°F (-18°C to -4°C) Saturated Suction
Temperatures.
Unloading application limits at saturated condensing
temperatures below 130°F (54°C): Can unload 1 bank
on any 4 or 6-cylinder 06D or 06E compressor.
Unloading more than 1 bank on any 6-cylinder 06D or
06E compressor in this medium temperature application
is not recommended.
High Temperature R-22 Applications: 25°F to
55°F (-4°C to 13°C) Saturated Suction
Temperatures.
Unloading application limits at SCT’s below 145°F
(63°C) and maximum superheat of 25°F (14°C). Can
unload 1 bank on any 4-cylinder 06D or 06E compres-
sor. Can unload 1 or 2 banks on any 6-cylinder 06D or
06E compressor per Figure 11.
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