Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: Second Term
Week: 6
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Pressure And Its Measurement: Practical Pressure Measurement Techniques.
Topic: Introduction to Refrigeration: Refrigeration Cycle
Subject Matter: Evaporation, compression, condensation, expansion

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define refrigeration.
State the four main stages of the refrigeration cycle.
Explain the process occurring in each stage of the refrigeration cycle.

Affective Domain:

Appreciate the importance of refrigeration in daily life.
Show interest in understanding the working principles of refrigeration systems.

Psychomotor Domain:

Trace the refrigerant flow on a refrigeration cycle chart.
Identify the main components of a refrigeration system.

Collaborate with peers to discuss the functions of refrigeration cycle components.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology (JSS 1-3) & Senior Secondary Curriculum for Trade Subjects.
State Unified Scheme of Work for Senior Secondary Schools.
Refrigeration and Air Conditioning Technology by William C. Whitman, William M. Johnson, and John Tomczyk.
https://www.waeconline.org.ng/e-learning/Refrigeration/REFRIGERATION%20AND%20AIR%20CONDITIONING.pdf
https://ncee.gov.ng/curriculum/trade-subjects/refrigeration-and-air-conditioning/

Instructional Materials

The teacher will teach this lesson with the aid of:

A diagram or chart of the basic refrigeration cycle.
A model of a compressor.
A sample condenser coil.
A sample evaporator coil.
Whiteboard/chalkboard and markers/chalk.

Rationale for the Lesson

Understanding the refrigeration cycle helps pupils to know how cooling is achieved in everyday appliances like refrigerators and air conditioners. This knowledge is important for grasping the fundamental principles of refrigeration and air conditioning technology, which has practical applications in homes and industries.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of heat, temperature, states of matter (solid, liquid, gas), and heat transfer methods (conduction, convection, radiation).

Lesson Content/Board Summary

Introduction to Refrigeration and the Refrigeration Cycle

Definition of Refrigeration

Refrigeration is the process of removing heat from a space or substance and maintaining its temperature below the ambient temperature.

Purpose of Refrigeration

The main purposes of refrigeration include:

Preserving perishable food items.
Storing medicines and chemicals.
Providing comfort cooling in homes and offices (air conditioning).
Industrial processes requiring low temperatures.

The Basic Refrigeration Cycle

The refrigeration cycle describes the continuous process by which a refrigerant absorbs heat from a low-temperature area and releases it to a high-temperature area. It involves a closed loop where the refrigerant changes state (liquid to gas and back to liquid) as it circulates through different components.

Stages of the Refrigeration Cycle

The four main stages of the refrigeration cycle are:

1. Evaporation

This is the process where the liquid refrigerant absorbs heat from the space being cooled and changes into a low-pressure, low-temperature vapour. This occurs in the evaporator coil, which is placed inside the refrigerated space.

Key points about evaporation:

Refrigerant absorbs latent heat from the surroundings.
Changes from liquid to vapour.
Occurs at low pressure and low temperature.

2. Compression

The low-pressure, low-temperature refrigerant vapour from the evaporator is drawn into the compressor. The compressor increases the pressure and temperature of the refrigerant vapour, making it a high-pressure, high-temperature vapour.

Key points about compression:

Increases the pressure of the refrigerant.
Increases the temperature of the refrigerant.
Requires external work (electricity).

3. Condensation

The high-pressure, high-temperature refrigerant vapour from the compressor flows into the condenser coil. Here, it releases heat to the cooler ambient air or water and changes back into a high-pressure liquid. This heat is dissipated to the surroundings.

Key points about condensation:

Refrigerant releases latent heat to the surroundings.
Changes from vapour to liquid.
Occurs at high pressure and high temperature.

4. Expansion (Throttling)

The high-pressure liquid refrigerant from the condenser passes through an expansion device (e.g., expansion valve or capillary tube). This device reduces the pressure of the refrigerant, causing its temperature to drop significantly, and it becomes a low-pressure, low-temperature liquid-vapour mixture, ready to enter the evaporator again.

Key points about expansion:

Reduces the pressure of the refrigerant.
Causes a significant drop in refrigerant temperature.
Prepares the refrigerant for heat absorption in the evaporator.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and reviews the previous lesson briefly. The teacher then introduces the new topic by asking pupils what they know about refrigerators or air conditioners and how they make things cold.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively.
Learning Point: Pupils recall previous knowledge and are introduced to the lesson topic.

Step 2: Definition of Refrigeration

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines refrigeration and explains its general purpose using common examples like food preservation. The teacher writes the definition on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and purpose of refrigeration.

Step 3: Overview of the Refrigeration Cycle

Time: 5 minutes
Teaching Skill: Illustration/Explanation
Teacher’s Activity: The teacher displays the refrigeration cycle chart and briefly explains that refrigeration is achieved through a continuous cycle involving changes in the refrigerant’s state. The teacher points out the four main components on the chart.
Pupils’ Activity: Pupils observe the chart and listen to the overview.
Learning Point: Pupils get a visual and conceptual introduction to the refrigeration cycle and its components.

Step 4: Evaporation and Compression Stages

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains the evaporation stage, using the evaporator coil to show where heat is absorbed. The teacher then explains the compression stage, demonstrating with the compressor model how pressure and temperature are increased. The teacher writes key points on the board.
Pupils’ Activity: Pupils observe the instructional materials, listen to the explanations, and take notes.
Learning Point: Pupils understand how the refrigerant absorbs heat and how its pressure and temperature are raised.

Step 5: Condensation and Expansion Stages

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains the condensation stage, showing the condenser coil and explaining how heat is rejected. The teacher then explains the expansion stage, describing how the refrigerant’s pressure and temperature are reduced before it returns to the evaporator. The teacher writes key points on the board.
Pupils’ Activity: Pupils observe, listen, and complete their notes.
Learning Point: Pupils understand how the refrigerant releases heat and how its pressure and temperature are lowered.

Step 6: Review of the Complete Cycle

Time: 3 minutes
Teaching Skill: Summarization/Tracing
Teacher’s Activity: The teacher uses the refrigeration cycle chart to trace the complete flow of the refrigerant through all four stages, emphasizing the continuous nature of the cycle.
Pupils’ Activity: Pupils follow the tracing on the chart and participate in a brief review discussion.
Learning Point: Pupils consolidate their understanding of the entire refrigeration cycle.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define refrigeration.
List the four main stages of the refrigeration cycle.
Explain what happens to the refrigerant in the evaporator.
What is the function of the compressor in the refrigeration cycle?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of the refrigeration cycle. The teacher gives homework: “Draw and label the basic refrigeration cycle.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils review the lesson’s main points and receive further practice.

Lesson Keywords

Refrigeration – The process of removing heat from a space or substance to maintain a lower temperature.
Refrigerant – A fluid used in refrigeration cycles that absorbs heat at a low temperature and rejects it at a higher temperature.
Evaporation – The stage where liquid refrigerant absorbs heat and changes into vapour.
Compressor – A mechanical device that increases the pressure and temperature of the refrigerant vapour.
Condensation – The stage where hot refrigerant vapour releases heat and changes back into liquid.
Expansion – The process where the pressure and temperature of the liquid refrigerant are reduced.
Evaporator – The component where the refrigerant absorbs heat from the space to be cooled.
Condenser – The component where the refrigerant releases heat to the surroundings.

Differentiation

For visual learners, the teacher will extensively use the cycle chart, compressor model, and coils to demonstrate the processes. For auditory learners, clear explanations and discussions will be emphasized. Kinesthetic learners can be encouraged to point out components on the chart or models. Struggling learners will receive additional support through simplified explanations and peer-to-peer discussions. Advanced learners will be challenged with questions about efficiency or applications of different refrigerants.

Note for teachers using this lesson plan

Ensure that all instructional materials are readily available and in good working condition before the lesson. Encourage pupils to ask questions and relate the concepts to everyday appliances they encounter. Emphasize safety precautions if handling actual components, even if they are non-functional models.