1. Introduction

Refrigeration and Air Conditioning are important applications of thermodynamics that deal with removing heat from a low-temperature region and transferring it to a higher-temperature region.

Normally, heat flows from higher temperature to lower temperature. Refrigeration systems use external work to reverse this natural flow of heat.

These systems are widely used in:

• Domestic refrigerators
• Air conditioners
• Cold storage plants
• Food preservation
• Industrial cooling

2. Refrigeration

Definition

Refrigeration is the process of removing heat from a low-temperature body or space and maintaining it at a temperature lower than the surroundings.

Example:

• Refrigerator
• Deep freezer
• Ice plant

Principle of Refrigeration

The basic principle is based on heat absorption during evaporation of a refrigerant.

When a refrigerant evaporates at low pressure, it absorbs heat from the surroundings, producing a cooling effect.

3. Air Conditioning

Definition

Air conditioning is the process of maintaining the temperature, humidity, cleanliness, and air motion of an enclosed space to achieve human comfort or industrial requirements.

Functions of Air Conditioning

Air conditioning controls:

1. Temperature
2. Humidity
3. Air purity
4. Air circulation

Types of Air Conditioning

1. Comfort Air Conditioning
   • Used in homes, offices, malls.
2. Industrial Air Conditioning
   • Used in industries where temperature and humidity must be controlled.

Example:

• Textile industry
• Pharmaceutical industry

4. Refrigeration Cycle

The most common refrigeration cycle is the Vapour Compression Refrigeration Cycle.

It consists of four main components:

1. Compressor
2. Condenser
3. Expansion valve
4. Evaporator

5. Vapour Compression Refrigeration Cycle

The vapour compression cycle consists of four thermodynamic processes.

Process 1–2: Compression

• Low-pressure refrigerant vapour enters the compressor.
• The compressor compresses the vapour.

Result:

• Pressure increases
• Temperature increases

The compressor requires mechanical work input.

Process 2–3: Condensation

• High-pressure vapour enters the condenser.
• Heat is rejected to surroundings.

Result:

• Vapour condenses into liquid refrigerant.

This process occurs at constant pressure.

Process 3–4: Expansion

• Liquid refrigerant passes through the expansion valve (throttle valve).

Result:

• Pressure drops suddenly
• Temperature decreases

This process is known as throttling process.

Process 4–1: Evaporation

• Low-pressure liquid enters the evaporator.
• Refrigerant absorbs heat from the surrounding space.

Result:

• Refrigerant evaporates into vapour
• Cooling effect is produced

6. Coefficient of Performance (COP)

The performance of a refrigeration system is measured by Coefficient of Performance (COP).$$COP_R = \frac{Refrigeration\ Effect}{Work\ Input}$$$$COP_R = \frac{Q_L}{W}$$

Where

• $Q_L$QL​ = Heat removed from the refrigerated space
• $W$W = Work input to compressor

Important Point

Higher COP means better efficiency of refrigeration system.

7. Vapour Absorption Refrigeration System

This system uses heat energy instead of mechanical work.

Main Components

1. Generator
2. Condenser
3. Expansion valve
4. Evaporator
5. Absorber
6. Pump

Common Working Fluids

• Ammonia–Water system
• Lithium bromide–Water system

Advantages

• Low electricity consumption
• Can use waste heat or solar energy

Disadvantages

• Lower efficiency compared to vapour compression system

8. Types of Refrigerants

A refrigerant is a working fluid used in refrigeration systems.

Examples

• Ammonia (NH₃)
• Freon (R-12, R-134a)
• Carbon dioxide (CO₂)

Properties of a Good Refrigerant

1. Low boiling point
2. High latent heat
3. Non-toxic
4. Non-flammable
5. Chemically stable
6. Environment friendly

9. Applications of Refrigeration and Air Conditioning

Domestic Applications

• Refrigerator
• Air conditioner
• Water cooler

Industrial Applications

• Food preservation
• Ice plants
• Chemical industries
• Pharmaceutical industries

Commercial Applications

• Shopping malls
• Hotels
• Hospitals
• Cinema halls

10. Difference Between Refrigeration and Air Conditioning

Refrigeration	Air Conditioning
Removes heat to produce cooling	Controls temperature, humidity, and air purity
Mainly for preservation	Mainly for human comfort
Used in refrigerators and freezers	Used in AC systems

11. Advantages

• Food preservation
• Comfortable living conditions
• Industrial process control
• Medical storage

12. Limitations

• High energy consumption
• Environmental impact of refrigerants
• Maintenance cost