1. LEGEND High press Low press Liquid vapour mixture
Direct expansion evaporator
Vapour
Expansion valve
Seawater
out
Liquid
Oil separator
Receiver with gauge glass
Refrigeration compressor
Condenser
Seawater in
Oil return to sump

2. Compressor Type
Reciprocating
Centrifugal
Screw

4. Compressors Reciprocating: Suction must be dry Low capacity
High leakage factor; air entry

5. Compressors Centrifugal: Not flexible to demand
Large installation ; high speed operation
Simple design ; wear to bearing only
Care as liquid may enter compressor

6. Screw Compressor Lobes Drive shaft Unloader piston Cylinder Bypass gas
Outlet
Slide
valve
Discharge
Port
Max Min
Inlet
Screw Compressor

7. Compressors: Screw: Large capacity
Oil injection for lubrication and oil film
Capacity control by sliding vanes

8. o-ring
drive end
rotating seal
seal retainer
cover plate
drive shaft
grub screw to secure seal retainer to shaft
spring
stationary seal
Mechanical Seal
jointing
securing bolt
oil

9. Gas to condenser
Gas from compressor
Float
Oil to compressor
crankcase
Oil

10. Condensers Shell and tube: Aluminium – brass tubes with fins
Iron plugs
Velocity < 2.5m/s to reduce erosion

11. Compressor Problems High Load leading to:
high temperature ; oil soluble in Freon
more oil carried away
liquid returning causing valve damage; also evaporation cause seizure
Moisture causing Freon and copper to react
Sticking of unloading gear
Broken valves causing overheating

12. High Temperature (cause)
Condenser
Compressor jacket cooling
High suction pressure
Leaky valves – recompression
Above rated speed
Choked discharge passages

13. Crankcase Oil Low pour point -35 oC Miscible with refrigerant
Anti foaming + pour point depressant
No air or moisture
S.G ~ 0.9
Viscosity index > 25
Low floc point – (wax precipitation)

14. Primary Refrigerant Halogenated hydrocarbons
Numerical code used for naming
Non toxic;
except ammonia – separate compartment
Design pressure related to maximum operational temperature expected.
Miscibility with oil – for easy retrieval

15. Comparison R12 Miscible with oil under all condition
30 % less refrigerating effect
R22
Miscible with oil up to -9oC
Water more soluble by ratio 3 : 1
more desiccant

16. Precautions with Freon
Goggles
No heating to cylinder or system if under pressure
Blow out gas before brazing
Max cap of cylinder < 85%
When charging :
inspect lines first.
use gauge
no charging of liquid to suction side
Frost bite – special medication to eyes ; no rubbing
Phosgene gas –ventilation important

17. Secondary Refrigerant
Save on:
primary refrigerant
high pressure piping
Intermediate temperature range possible with injection
Improve suction as need for high velocities to improve return of oil reduced

18. Brine Mixture of Calcium Chloride & Water
To prevent corrosion maintained at Ph 8 to 8.5 by adding say hydrochloric acid

19. Operating Temperature oC -21 -23 -26 -29 -32 -34
Specific Gravity 15o C
1.24
1.25
1.26
1.265
1.275
1.28
Operating Temperature oC
-21
-23
-26
-29
-32
-34
Freezing Temperature oC
-30
-35
-37
-41
-43
Specific Heat Kcal./Kg
.685
.678
.671
.667
.661
.658