Refrigeration and Air Conditioning Basic Principles Machineries Plant Diagnostic Air Conditioning Cargo Refrigeration Environmental Matters

Key Factors Coefficient of Performance Capacity Control Refrigeration Effect

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

Meat room at -18oC Heat energy E1 at low temp. being passed to refrigerant Energy E3 thrown out to sea Compression energy E2

+ = Heat energy E1 at low temp. Compression energy E2 Energy E3 thrown out to sea + = WASTE ENERGY TO SEA OUR OBJECTIVE WE NEED TO SPEND THIS

Coefficient of Performance COP is ratio of Energy Extracted E1over Energy Spent E2

COP Energy Extracted = 304 -150 = 154kJ/kg Energy Spent = 365 -304 = 61 kJ/kg COP = 154 / 61 = 2.52

Capacity Control Constant Pressure = Supply to Evaporator = Constant Temperature Supply to Evaporator = Removal Quantity of refrigerant α Load

Back pressure valve Suction line of warmer evaporator Pressure higher ; thus higher temperature

Control Methods Start /Stop Speed Several compressors in parallel Bypass hot gas Unloading (reciprocating) Throttle suction (centrifugal) Slide valve (screw)

Safety Spring Delivery Valve Suction Valve Unloader pin

to unload Capacity Reduction Gear Suction valve Push rod Moving ring Operating rod Oil servo: manual or auto Capacity Reduction Gear to unload

Refrigerating Effect Depends on: Refrigerant mass circulated per unit time Refrigerating effect per unit mass circulated

Throttling Devices Maintain pressure difference Meter correct amount for varying load Reduce boiling point by reducing pressure

AUTOMATIC EXPANSION VALVE Adjusting screw to alter spring pressure Refrigerant OUT Spring Pressure - Opening Action Spring Diaphragm Throttling orifice Refrigerant Pressure - Closing Action Refrigerant Refrigerant (liquid) IN EVAPORATOR

THERMOSTATIC EXPANSION VALVE (TEV) (internally equalised) Refrigerant (slightly superheated gas) OUT Refrigerant Remote bulb Diaphragm Throttling orifice Refrigerant Spring Adjusting screw to alter spring pressure Refrigerant (liquid) IN EVAPORATOR

THERMOSTATIC EXPANSION VALVE (TEV) (externally equalised) To overcome this problem, an externally equalised thermostatic Refrigerant (slightly superheated gas) OUT Diaphragm Throttling orifice Equalising connection Refrigerant Spring Remote bulb Adjusting screw to alter spring pressure Refrigerant (liquid) IN

Desirable properties of refrigerant HIGH Latent heat of evaporation smaller mass flow for same effect Specific heat at liquid state less flash gas LOW Specific volume smaller piping, compressor Low compression ratio lower pressure required Specific heat at vapour state less surface for superheat

Above saturated vapour or super-heated region Pressure (bar) Vapour to Liquid transformation in CONDENSER Enthalpy (kJ per kg of refrigerant) Saturated liquid line Below saturated liquid or sub-cooled region Saturated vapour line Above saturated vapour or super-heated region Liquid to vapour transformation in EVAPORATOR

Superheating

Subcooling