1. Refrigeration and Air conditioning

2. Lesson Plan Vapour compression refrigeration cycle
Components of a refrigeration system
Pressure enthalpy chart
superheating & sub-cooling
Heat exchanger
Coefficient of performance ( COP )
System Capacity
Direct and Indirect Expansion System
Back Pressure Regulating valve
Types of compressor
Oil Separator
Filter/Drier
Throttling device
Capacity control Method

3. Basic refrigeration cycle:
Heat energy flows from a hot region to a cooler region.
Vapour Compression Refrigeration System uses a circulating refrigerant as a medium which
1) absorbs & removes heat from space to be cooled
2) rejects the heat elsewhere (cooler)
Cold room
cooler
Cooling water
Heat energy
Refrigerant flow

4. Vapour Compression System
Liquid receiver
4 numbers principle components :
Evaporator
Compressor
Condenser
Expansion Valve
Heat out
Liquid
Condenser
High Pressure Side
Hot Gas
Compressor
Expansion
valve
Low Pressure Side
Evaporator
Gas
Heat in

5. Vapour Compression System
Liquid receiver
EVAPORATOR:
The evaporator coils are located in the compartment to be cooled.
The low pressure liquid refrigerant ,after passing through the expansion valve, expands.
Takes in heat from the surrounding and evaporates.
The gas is then sucked up by the compressor.
Heat out
Liquid
Condenser
High Pressure Side
Hot Gas
Compressor
Expansion
valve
Low Pressure Side
Evaporator
Gas
Heat in

6. Vapour Compression System
Liquid receiver
COMPRESSOR :
Compresses the refrigerant (gaseous state).
Raising its Temperature & Pressure.
Discharges refrigerant to Condenser.
Heat out
Liquid
Condenser
High Pressure Side
Hot Gas
Compressor
Expansion
valve
Low Pressure Side
Evaporator
Gas
Heat in

7. Vapour Compression System
Liquid receiver
LIQUEFACTION:
Hot refrigerant gas cooled in the condenser.
Condensed liquid refrigerant flows into a receiver.
Then liquid refrigerant flows to the expansion valve.
Heat out
Liquid
Condenser
High Pressure Side
Hot Gas
Compressor
Expansion
valve
Low Pressure Side
Evaporator
Gas
Heat in

8. Vapour Compression System
Liquid receiver
EXPANSION:
The expansion valve acting as a regulating valve, limits the amount of refrigerant flowing through.
Resulting in reduction of pressure of the liquid and expansion takes place.
Heat out
Liquid
Condenser
High Pressure Side
Hot Gas
Compressor
Expansion
valve
Low Pressure Side
Evaporator
Gas
Heat in

9. P-H chart ( Pressure – Enthalpy chart )
Pressure – Absolute pressure
Unit : bar , psi
Enthalpy – Total amount of energy per unit weight of substance.
Unit : BTU / Lb or kJ / kg
The lines ,saturated liquid & vapour respectively are plots of pressure vs enthalpy for the saturated state of a given refrigerant.
This chart is used to understand the property changes that takes place in each phase of the cycle.
Saturated vapour line
Saturated liquid line
Sub-cooled region
Sub cooled liquid
Liquid – vapour
mixture
Superheated region

10. Refrigeration Cycle : Pressure-Enthalpy graph
Enthalpy – Total amount of energy per unit weight of substance.
Unit : BTU / Lb or kJ / kg
Entropy – Measure of heat dispersion in a system divided by temperature.
Unit : BTU / Lb / deg change
or kJ / kg / deg change for a
substance.

11. Ideal Refrigeration Cycle : Pressure-Enthalpy chart
Liquid vapour mixture
Sub cooled liquid
Superheated vapour 4 3
Pressure (absolute) P2 P1 1 2
Enthalpy ( BTU / lbs or KJ / kg )

12. Refrigeration Cycle : Pressure-Enthalpy chart
Non ideal Refrigeration Cycle : Pressure – Enthalpy chart , showing superheating & sub cooling
Vapour to Liquid
transformation in
CONDENSER
Superheated
Liquid vapour mixture
Sub cooled liquid
Superheated vapour 4
subcooling 3
Pressure (absolute)
Throttling at expansion valve
Liquid vapour mixture
Work done in the compressor 2 1
Liquid to Vapour
Transformation in
EVAPORATOR
superheated
Enthalpy ( BTU / lbs or KJ / kg )

13. Enthalpy ( BTU / lbs or KJ / kg )
Non ideal Refrigeration Cycle : Pressure – Enthalpy chart , showing superheating & sub cooling
Vapour to Liquid
transformation in
CONDENSER
Superheated vapour
Sub cooled liquid 4 3
Throttling at expansion valve
Pressure (absolute)
Liquid vapour mixture
Work done in the compressor 1
Liquid to Vapour
Transformation in
EVAPORATOR 2 H1 H2 H3
Enthalpy ( BTU / lbs or KJ / kg )
The amount of heat that the refrigerant absorb must equal the cooling load.
(1) Refrigerant cooling load ( F ) = cooling load / ( H2 – H1)
(2) Work done by compressor = F x ( H3 – H2 )
(3) Heat rejected by condenser = F x ( H3 – H1 )
(4) Heat absorbed by evaporator = F x ( H2 – H1 )
Coefficient of Performance (COP) = heat absorbed by refrigerant / Energy required driving compressor
= ( H2 – H1) / ( H3 – H2)

14. Pressure-Enthalpy chart
1-2 : EVAPORATOR – extraction of heat from room
2-3 : COMPRESSOR – compression work
3-4 : CONDENSER – energy thrown to sea
4-1 : EXPANSION VALVE – throttling at the expansion valve
For each kg of refrigerant flow ,
Energy extracted from meat room : = 154 KJ / kg
Work spent on compressor = 365 – 304 = 61 KJ / Kg
Coefficient of Performance ( COP ) =
Energy extracted from room / Energy spent
= 154 / 61 or 2.52
Pressure
( bar )
Vapour to Liquid
transformation in
CONDENSER at 42 deg C 4 3 16
Throttling at expansion valve
Work done in the compressor
3.2
Liquid to Vapour
Transformation in
EVAPORATOR at -13 deg C 2 1
150
304
365
Enthalpy ( KJ / kg of refrigerant )

15. Pressure – Enthalpy chart , of a practical cycle (refer to page 8)
Effects of pressure loss resulting from friction.

16. Superheating & Sub-cooling
evaporator
refrigerant control (expansion valve)
Saturated suction vapour
Saturated liquid
Heat exchanger
Sub cooled liquid
Superheated suction vapour
receiver
compressor
Page 7
condenser
Improvement in cycle efficiency with a heat exchanger – as compared to another cycle where vapour is superheated without producing any useful cooling

17. Refrigeration system capacity
Rate at which system removes heat from.
Rate depends :
(1) mass of refrigerant circulated per unit time
(2) refrigerating effect per unit mass circulated
(undercooling increases the refrigerating effect)

18. Two systems employed: Direct Expansion System
Indirect expansion system
aka Brine System

19. Direct Expansion System : Provisional Refrigeration System
Thermostat
Purging line
To FISH ROOM
Condenser
expansion valve
Solenoid
stop valve
Drier
receiver
Cooling water in / out T1
Sight glass
Oil separator
Capillary tube
Fan / blower
Evaporator
To VEGETABLE ROOM
Oil return to compressor sump
HP pressure switch
Bulb
HP pressure gauge T2
MEAT ROOM
Oil pressure gauge
Refrigerant compressor
Oil pressure switch
Temperature
sensor
LP pressure gauge
Back pressure regulating valve
From FISH ROOM
LP pressure switch
From VEGETABLE ROOM
: Refrigerant flow

20. Indirect Expansion (Brine System)
Thermostat
Brine
header
tank
Condenser / Receiver
Solenoid
stop valve
expansion valve
Drier
pump
Cooling water in / out T1
Sight glass
Oil separator
Capillary tube
Evaporator
Oil return to compressor sump
Bulb
HP pressure switch T2
Refrigerant compressor
Oil pressure switch
Temperature
sensor
Secondary refrigerant to various compartment
LP pressure switch
: Refrigerant flow

21. Back pressure regulating valve
Normally fitted to higher temperature rooms, ie the vegetable room
not for the fish room or meat room.
Purpose :
Act as system balancing diverters –
a) When all solenoid valves are opened, the valve restrict liquid flowing into the vegetable room &
therefore deliver the bulk to the colder rooms.
b) Limits the pressure drops across the expansion valve by giving a set minimum pressure in the
evaporator coil. Prevents cold air blowing directly onto delicate vegetables.

22. Refrigerant Compressor types:
Reciprocating
Rotary
Centrifugal
Screw

23. Oil Separator Page 12 Gas from compressor Gas to condenser
Internal baffles
Oil to compressor crankcase
Oil
Page 12
Float

24. Liquid-line Filter / Drier
Course filter to remove large particles
Drying agent : silica gel or activated alumina
Desiccant
(dehydrating material)
Refrigerant in
Clean,dry refrigerant
Felt pad
Fine filter to remove small particles
Page 13

25. Condenser: Air cooled type – up to 5 hp
Large capacity – shell & tube type , SW cool
Tubes – aluminium brass (option ext. fins)
Water velocity < 2.5 m/s minimise erosion
Anodes – avoid corrosion non ferrous metals

26. Throttling device:
Metering of refrigerant – rate suitable to maintain designed operating pressures at different load.
Maintain pressure differential between HP & LP side.
The pressure of the refrigerant is reduced as it passes through the small orifice
of the throttling device. With the reduction in pressure, the corresponding
boiling point of the liquid is reduced.
Types of throttling devices:
Hand expansion valves
Automatic constant pressure expansion valve
Thermostatic expansion valve
Externally equalized expansion valve
Pressure balancing expansion valve
Expansion valves with centrifugal type distributors
Flow control device for flooded evaporators

27. Expansion valve automatic expansion valve thermostatic expansion valve
externally equalised thermostatic expansion valve

28. Automatic expansion valve
Page 18

29. Thermostatic expansion valve (TEV)
Page 19

30. External equalised thermostatic expansion valve
Page 20

31. Capacity control methods
To maintain constant temperature, a constant pressure must be present in the EVAPORATOR. Ideally, the compressor should remove from the EVAPORATOR exactly the volume of refrigerant that boils off in it. Change in loading : change in quantity of boiling off the refrigerant.
Manual start/stop
Speed variation
Cylinder unloading reciprocating compressor
Suction side throttling centrifugal compressor
Inlet guide vane centrifugal compressor
Hot gas bypass
Compressor in parallel
Slide valve
Screw compressor - control effective working length of rotor.

32. Unloading device

33. Screw compressor NORMAL LOADING Page 12 DRIVE SHAFT INLET LOBES Max
Min
DISCHARGE PORT
UNLOADING PISTON
BYPASS GAS
OUTLET
CYLINDER
SLIDE VALVE
NORMAL LOADING
Page 12

34. Screw compressor REDUCE LOADING DRIVE SHAFT INLET LOBES Max Min
DISCHARGE PORT
UNLOADING PISTON
BYPASS GAS
OUTLET
CYLINDER
SLIDE VALVE
REDUCE LOADING