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

Compressor Type Reciprocating Centrifugal Screw

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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