1. The Refrigeration Process
Chapter 2
The Refrigeration Process

2. Learning Objectives
After completing the material in this chapter, the student should be able to:
Describe the basic vapor-compression refrigeration cycle.
List the basic components that make up a vapor-compression refrigeration system.
Describe the function of a compressor.
List various types of compressors.
Describe the function of the metering device.
List three commonly used metering devices.
Describe the function of the evaporator.

3. The Refrigeration Process
Four major components enable heat transfer:
Evaporator
Compressor
Condenser
Metering device

4. The Refrigeration Process
Components of a refrigeration system.

5. Pressure/Temperature Relationship
As the pressure of a refrigerant changes, so does the temperature.
An increase in pressure will cause an increase in temperature.
An increase in temperature will cause an increase in pressure.

6. Pressure/Temperature Relationship
This holds true for saturated refrigerants only:
Mixture of liquid and vapor
Refrigerants undergoing a change of state
Superheated and subcooled refrigerant do not follow the pressure/temperature relationship

7. Pressure/Temperature Relationship

8. Superheat
It is the amount of sensible heat added to refrigerant after it has boiled into a vapor.
The vapor is heated above its saturation temperature.

9. Subcooling
It is the amount of sensible heat removed from refrigerant after it has condensed into a liquid.
The liquid is cooled below its saturation temperature.

10. Evaporators
The purpose of an evaporator is to absorb heat from the space that is to be cooled.
It must be at a lower temperature than the medium being cooled.
Refrigerant in the evaporator boils from a liquid to a vapor at a low pressure and a low temperature.

11. The evaporator coil is located inside an air handler.
Evaporators
The evaporator coil is located inside an air handler.

12. Compressors Pump the refrigerant through the refrigeration system.
Create the pressure difference between high and low side of system.
They are considered to be vapor pumps.
Compressors cannot compress or pump liquid.

13. Compressors Three compressor types: Reciprocating compressors
Rotary compressors
Scroll compressors

14. Principle of a reciprocating compressor.
Compressors
Principle of a reciprocating compressor.

15. Principle of a rotary compressor.
Compressors
Principle of a rotary compressor.

16. Principle of a scroll compressor.
Compressors
Principle of a scroll compressor.

17. Condensers
It is the component responsible for rejecting heat from the system.
It must be located outside the refrigerated space.
Refrigerant in the condenser must be warmer than the condensing medium passing over it.
The refrigerant condenses from a high-temperature, high-pressure vapor to a high-pressure, high-temperature liquid.

18. A condenser used in split-type central air conditioning systems.
Condensers
A condenser used in split-type central air conditioning systems.

19. Metering Devices
Responsible for reducing the pressure and temperature of the refrigerant in a refrigeration system.
Restricts the flow of refrigerant from the condenser.
Changes a high-pressure, high-temperature liquid into a low-pressure, low-temperature liquid.

20. Metering Devices Three types of metering devices: Capillary tube
Fixed bore metering device
Does not respond well to load changes
Automatic expansion valve
Maintains a constant evaporator pressure
Evaporator and spring pressure control valve operation
Thermostatic expansion valve
Maintains constant superheat in the evaporator
Spring, bulb, and evaporator pressure control valve operation

21. Capillary Tube

22. Automatic Expansion Valve

23. Thermostatic Expansion Valve

24. Refrigerants in the Residential System
Currently the most popular refrigerant used in residential air conditioning
R-410A:
Will soon be commonly used in residential air conditioning systems

25. Summary
The vapor-compression refrigeration cycle is a repeating cycle, consisting of a compressor, a condenser, a metering device, and an evaporator.
The compressor changes the refrigerant from a low-temperature, low-pressure, superheated vapor to a high-temperature, high-pressure, superheated vapor.
Three common types of compressors are the rotary, the reciprocating, and the scroll.

26. Summary
The condenser rejects heat from the system and changes the refrigerant from a high-temperature, high-pressure vapor into a high-temperature, high-pressure liquid.
Condensers used on residential systems are typically air cooled.
Latent-heat transfers cannot be measured with a thermometer.
When the temperature of a substance changes, a sensible-heat transfer takes place.

27. Summary
The metering device controls the flow of refrigerant to the evaporator:
It changes a high-temperature, high-pressure liquid into a low-temperature, low-pressure liquid
Three common metering devices are the capillary tube, the automatic expansion valve, and the thermostatic expansion valve.
The refrigerant in the evaporator absorbs heat into the refrigeration system.