Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 6
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Compressors: Construction of Screw and Rotary Compressors.
Topic: Compressors
Subject Matter: Working principles of compressors, compression process, suction and discharge, refrigerant flow.

Specific Objectives

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

Cognitive Domain:

Define a compressor in a refrigeration system.
Explain the compression process.
Describe the concepts of suction and discharge in a compressor.
Outline the flow of refrigerant through the compressor.

Affective Domain:

Appreciate the importance of compressors in refrigeration and air conditioning.
Develop interest in understanding the internal workings of refrigeration components.

Psychomotor Domain:

Identify the suction and discharge ports on a compressor model or diagram.
Sketch a simple diagram illustrating the refrigerant flow through a compressor.

Participate actively in class discussions about compressor operations.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology (JSS 1-3) / Senior Secondary Education Curriculum for Trade Subjects.
State Unified Scheme of Work for Refrigeration And Air Conditioning (SSS 1).
Akinola, O. (2018). Refrigeration and Air Conditioning Technology for Senior Secondary Schools. Ibadan: Spectrum Books.

Instructional Materials

The teacher will teach this lesson with the aid of:

A compressor cycle chart.
A small compressor motor model or diagram.
Flow arrows to indicate refrigerant direction.
Whiteboard and markers.

Rationale for the Lesson

Understanding the working principles of compressors is important because they are fundamental components in all refrigeration and air conditioning systems. This knowledge helps pupils grasp how these systems cool spaces and preserve items, which is relevant to everyday life and potential future careers in the trade.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of the components of a simple refrigeration system and the concept of heat transfer.

Lesson Content/Board Summary

Compressors: Working Principles

Definition of a Compressor

A compressor is a mechanical device that increases the pressure of a gas (refrigerant vapour) by reducing its volume. It is the “heart” of the refrigeration system, circulating the refrigerant and increasing its temperature and pressure before it enters the condenser.

The Compression Process

The compression process involves taking low-pressure, low-temperature refrigerant vapour from the evaporator and converting it into high-pressure, high-temperature vapour. This is achieved by the mechanical action of the compressor, which reduces the volume of the gas, thereby increasing its pressure and temperature.

Suction and Discharge

These are critical phases in the compressor’s operation:

Suction: This is the intake phase where the compressor draws in low-pressure, low-temperature refrigerant vapour from the evaporator. The suction line connects the evaporator to the compressor’s suction port.
Discharge: This is the expulsion phase where the compressor pushes out high-pressure, high-temperature refrigerant vapour into the condenser. The discharge line connects the compressor’s discharge port to the condenser.

Refrigerant Flow through the Compressor

The flow of refrigerant through the compressor is a continuous cycle:

Low-pressure, low-temperature refrigerant vapour enters the compressor through the suction port from the evaporator.
Inside the compressor, the vapour is compressed, increasing its pressure and temperature significantly.
The high-pressure, high-temperature refrigerant vapour then exits the compressor through the discharge port, flowing towards the condenser.
This process ensures continuous circulation and conditioning of the refrigerant in the system.

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 asks pupils to mention any device that uses a compressor (e.g., refrigerator, air conditioner) to introduce the topic of compressors.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall previous knowledge and are prepared for the new topic.

Step 2: Definition of a Compressor

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines a compressor as a mechanical device that increases the pressure of refrigerant vapour by reducing its volume. The teacher explains its role as the “heart” of the refrigeration system.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the basic definition and function of a compressor.

Step 3: The Compression Process

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains how the compressor takes low-pressure vapour and converts it to high-pressure vapour using the compressor cycle chart and the motor model to illustrate the mechanical action.
Pupils’ Activity: Pupils observe the chart and model, listen to the explanation, and describe the process in their own words.
Learning Point: Pupils grasp the concept of pressure and temperature increase during compression.

Step 4: Suction and Discharge

Time: 8 minutes
Teaching Skill: Identification/Illustration
Teacher’s Activity: The teacher clearly explains and points out the suction and discharge ports on the compressor model/diagram. The teacher uses flow arrows to indicate the direction of refrigerant during suction and discharge.
Pupils’ Activity: Pupils identify the suction and discharge ports and understand their functions.
Learning Point: Pupils can differentiate between the suction and discharge phases and their physical locations.

Step 5: Refrigerant Flow through the Compressor

Time: 7 minutes
Teaching Skill: Sequencing/Description
Teacher’s Activity: The teacher describes the complete path of refrigerant as it enters the compressor (suction), gets compressed, and then exits (discharge), linking it to the overall refrigeration cycle.
Pupils’ Activity: Pupils trace the refrigerant flow on the chart and in their notes.
Learning Point: Pupils understand the continuous movement of refrigerant through the compressor within the system.

Step 6: Class Activity/Discussion

Time: 5 minutes
Teaching Skill: Group Work/Discussion
Teacher’s Activity: The teacher divides pupils into small groups to discuss the main points of the lesson and answer questions on the board about the importance of the compressor.
Pupils’ Activity: Pupils discuss in groups and share their answers with the class.
Learning Point: Pupils reinforce their understanding through peer interaction and discussion.

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 a compressor.
Explain what happens to the refrigerant vapour during the compression process.
Differentiate between the suction and discharge phases of a compressor.
Outline the flow of refrigerant through the compressor.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key learning points of the lesson and assigns homework, asking pupils to draw a simple diagram of a compressor showing its suction and discharge lines.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Compressor – A mechanical device that increases the pressure of a gas by reducing its volume.
Refrigerant – A substance used in refrigeration cycles that undergoes phase changes to absorb and release heat.
Suction – The process where a compressor draws in low-pressure, low-temperature refrigerant vapour.
Discharge – The process where a compressor expels high-pressure, high-temperature refrigerant vapour.
Compression – The act of increasing the pressure of a gas by reducing its volume.

Differentiation

For visual learners, the teacher will make extensive use of the compressor cycle chart and the physical model. Auditory learners will benefit from the detailed explanations and discussions. Kinesthetic learners will be encouraged to interact with the model and draw diagrams. Pupils who grasp concepts quickly can be given additional questions about different types of compressors or their applications.

Note for teachers using this lesson plan

Ensure the compressor model or diagram is clearly visible to all pupils. Encourage active participation and questions to clarify any misconceptions about pressure and temperature changes. Emphasize the connection between the compressor’s function and the overall cooling effect in refrigeration systems.