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3.8 Oil Cooler Selection
An oil cooler is required on all Carlyle screw com-
pressor systems not operating in the range indi-
cated in the previous section. This is generally for
systems requiring lower suction temperatures or
higher discharge temperatures. Also, 05T direct
drive compressor systems with discharge tem-
peratures that may exceed 180 F (82 C) always
require an oil cooler. The oil cooler must be sized
based on an oil flow rate of approximately 2 gal-
lons per minute (7.6 liters/minute) per compres-
sor. (The actual oil flow rate will vary based on
pressure ratio of the application. The precise oil
cooler load may be obtained from the Carlyle
compressor selection software.) The maximum oil
temperature leaving the oil cooler is 170 F (77 C)
and the maximum temperature entering the oil
cooler is 200 F (93 C) (based on discharge tem-
perature control). The oil cooler load is nominally
1 ton (3.5 kilowatts) per compressor, but may be
calculated with the above data and oil manufac-
turer's specifications. In applications which
require oil cooling some means of controlling the
oil temperature entering the compressor is
required.
Several possible methods are;
• Oil cooler fan cycling based on oil outlet tem-
perature (10F∆T)
• Oil cooler bypass via a solenoid valve controlled
off of oil cooler entering temperature
• Use of a mixing valve to maintain a constant oil
temperature entering the compressor
• Some combination of the three methods listed
above
The oil may be cooled by means of an air cooled,
refrigerant cooled, or water cooled oil cooler.
Carlyle offers 4 sizes of air cooled oil coolers for
Oil Cooler Models Available
Fan Speed 60Hz
KH51ZZ181 (2 Compressors Max)*
KH51ZZ182 (3 Compressors Max)*
KH51ZZ183 (4 Compressors Max)*
KH51ZZ184 (5 Compressors Max)*
Oil Cooler Models Available
Fan Speed 50Hz
KH51ZZ181 (2 Compressors Max)*
KH51ZZ182 (3 Compressors Max)*
KH51ZZ183 (4 Compressors Max)*
KH51ZZ184 (5 Compressors Max)*
*Maximum Number of Compressors Based on Oil Cooler Pressure Drop of Less Than 6 PSID (.41 bar)
use with the 05T and 06T screw compressor.
Following is selection criteria for the various mod-
els along with dimensional information.
If using a refrigerant cooled oil cooler, the oil
cooling load will need to be subtracted from
either the compressor's evaporator capacity or
the subcooling capacity. Using compressor suc-
tion pressure will led to a reduction in system
capacity since some of the compressor suction
mass flow will now come from the oil cooler.
Using the compressor interstage port for oil cool-
ing will not reduce the compressor suction
pumping capacity but will indirectly reduce sys-
tem capacity by decreasing the compressor's
ability to do liquid subcooling. The additional
mass flow from the oil cooler to the interstage will
increase the interstage pressure. This will prevent
the subcooler from achieving the lowest possible
liquid temperature. Both systems require hold
back valves to prevent the oil temperature from
dropping below 80 F (27 C).
Also, caution must be taken to ensure that the
return gas to the compressor is not too hot. For
more information, contact Carlyle Application
Engineering.
The oil cooler represents a heat source that may
be used for heat reclaim processes such as hot
water preheat. Since the oil cooler rejects dis-
charge heat, the heat rejection from the oil cooler
can be subtracted from the heat rejection
required by the system condenser. This may lead
to a smaller size condenser. Condenser circuiting
may also be used for oil cooling; however, pres-
sure drops must be taken into account for mini-
mum oil pressure differential to the compressors.
A mixing valve is recommended for all oil coolers
circuited through a remote air-cooled condenser.
Oil Cooling Capacity @ Ambient Air Temperature
95ºF
100ºF
(35ºC)
(38ºC)
32,100 Btu/Hr
30,600 Btu/Hr
(9,405 W/Hr)
(8,966 W/Hr)
69,100 Btu/Hr
65,700 Btu/Hr
(20,246 W/H)
(19,250 W/Hr)
102,600 Btu/Hr
97,700 Btu/Hr
(30,061 W/Hr)
(28,626 W/Hr)
134,100 Btu/Hr
127,700 Btu/Hr
(39,291 W/Hr)
(37,416 W/Hr)
Oil Cooling Capacity @ Ambient Air Temperature
95ºF
100ºF
(35ºC)
(38ºC)
32,200 Btu/Hr
28,800 Btu/Hr
(9,405 W/Hr)
(9,435 W/Hr)
63,700 Btu/Hr
60,600 Btu/Hr
(18,664 W/H)
(17,756 W/Hr)
94,900 Btu/Hr
90,400 Btu/Hr
(27,805 W/Hr)
(26,487 W/Hr)
123,400 Btu/Hr
117,500 Btu/Hr
(26,156 W/Hr)
(34,427 W/Hr)
16
105ºF
110ºF
(41ºC)
(43ºC)
29,000 Btu/Hr
27,600 Btu/Hr
(8,497 W/Hr)
(8,087 W/Hr)
62,400 Btu/Hr
59,100 Btu/Hr
(18,283 W/Hr)
(17,316 W/Hr)
92,800 Btu/Hr
87,900 Btu/Hr
(27,190 W/Hr)
(25,755 W/Hr)
121,300 Btu/Hr
114,900 Btu/Hr
(35,541 W/Hr)
(33,665 W/Hr)
105ºF
110ºF
(41ºC)
(43ºC)
27,300 Btu/Hr
25,900 Btu/Hr
(8,438 W/Hr)
(7,999 W/Hr)
57,600 Btu/Hr
54,600 Btu/Hr
(16,877 W/Hr)
(15,998 W/Hr)
85,900 Btu/Hr
81,400 Btu/Hr
(25,168 W/Hr)
(23,850 W/Hr)
111,600 Btu/Hr
105,800 Btu/Hr
(32,699 W/Hr)
(30,999 W/Hr)
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