Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 2nd Term
Week: 8
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Introduction To Refrigeration: Layout Diagrams of Refrigeration System.
Topic: Refrigerants
Subject Matter: Definition of refrigerants, cooling function, heat absorption

Specific Objectives

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

Cognitive Domain:

Define a refrigerant.
Explain the cooling function of refrigerants.
Describe how refrigerants absorb heat.

Affective Domain:

Appreciate the importance of refrigerants in refrigeration and air conditioning systems.
Show interest in learning about the properties and handling of refrigerants.

Psychomotor Domain:

Identify a refrigerant cylinder and associated safety labels.
State at least two safety precautions when handling refrigerants.

Participate actively in class discussions about refrigerants.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary School (Refrigeration and Air Conditioning).
State Unified Scheme of Work for Senior Secondary Schools.
Basic Refrigeration and Air Conditioning Technology for Senior Secondary Schools.

Instructional Materials

The teacher will teach this lesson with the aid of:

A refrigerant cylinder.
A pressure hose.
Safety labels.
Charts showing the refrigeration cycle.

Rationale for the Lesson

This lesson helps pupils understand the fundamental substance that makes refrigeration and air conditioning systems work. Knowing what refrigerants are and how they function is important for understanding their role in cooling and preserving items in daily life, as well as for future studies in this trade.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of heat, temperature, and the states of matter (solid, liquid, gas).

Lesson Content/Board Summary

Refrigerants

Definition of Refrigerants

Refrigerants are substances, usually fluids, used in refrigeration and air conditioning systems to absorb heat from one area and release it into another. They undergo phase changes (evaporation and condensation) to achieve cooling.

Cooling Function of Refrigerants

The primary function of a refrigerant is to create a cooling effect. This is achieved through a continuous cycle where the refrigerant changes between liquid and gas states. When it evaporates, it absorbs heat from the space to be cooled, and when it condenses, it releases that heat to the surroundings.

Heat Absorption by Refrigerants

Refrigerants absorb heat mainly through the process of evaporation. The following explains how:

In the evaporator coil, the liquid refrigerant absorbs heat from the surrounding air or medium.
As it absorbs heat, the refrigerant changes from a low-pressure liquid to a low-pressure gas (vapour). This phase change requires a significant amount of heat energy, which is drawn from the area being cooled.
This process effectively removes heat from the desired space, thereby lowering its temperature.

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 what they think is inside a refrigerator or air conditioner that makes it cold. The teacher introduces the topic “Refrigerants” as the substance responsible for cooling.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall previous knowledge and are introduced to the new topic.

Step 2: Definition of Refrigerants

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines refrigerants, explaining that they are working fluids used in refrigeration cycles. The teacher uses the refrigerant cylinder and safety label to show pupils what refrigerants look like in their container and the associated warnings.
Pupils’ Activity: Pupils listen, take notes, and observe the instructional materials.
Learning Point: Pupils understand the definition of refrigerants and can identify their containers.

Step 3: Cooling Function of Refrigerants

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how refrigerants create a cooling effect by absorbing heat from one area and releasing it into another. The teacher may use a chart showing the basic refrigeration cycle to illustrate this concept.
Pupils’ Activity: Pupils listen, ask questions, and try to understand the refrigeration cycle.
Learning Point: Pupils understand the primary role of refrigerants in cooling.

Step 4: Heat Absorption by Refrigerants

Time: 10 minutes
Teaching Skill: Elaboration
Teacher’s Activity: The teacher elaborates on the process of heat absorption, focusing on the phase change (evaporation) in the evaporator coil. The teacher explains that as liquid refrigerant evaporates, it takes heat from the surrounding environment.
Pupils’ Activity: Pupils listen carefully and take notes on the process of heat absorption.
Learning Point: Pupils understand how refrigerants specifically absorb heat during their phase change.

Step 5: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

What is a refrigerant?
Explain the main cooling function of a refrigerant.
Describe how refrigerants absorb heat in a refrigeration system.
Mention one safety precaution when handling refrigerants.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 6: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definition, cooling function, and heat absorption process of refrigerants. The teacher assigns homework: “List three common types of refrigerants and their uses.”
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their understanding and are given an activity to reinforce learning.

Lesson Keywords

Refrigerant – A substance used in refrigeration and air conditioning systems to absorb and release heat.
Cooling Function – The ability of a refrigerant to remove heat from a space, thereby lowering its temperature.
Heat Absorption – The process by which a refrigerant takes in heat energy, typically during its phase change from liquid to gas.
Evaporation – The process where a liquid changes into a gas, absorbing heat from its surroundings.
Condensation – The process where a gas changes into a liquid, releasing heat to its surroundings.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research different types of refrigerants and their environmental impacts. For pupils who need more support, the teacher can provide simplified diagrams of the refrigeration cycle and offer one-on-one explanations.

Note for teachers using this lesson plan

Ensure that all instructional materials, especially the refrigerant cylinder and pressure hose, are handled safely and are only used for demonstration purposes. Emphasize the importance of safety when discussing refrigerants. Encourage pupils to ask questions to clarify any doubts about the abstract concepts of heat transfer and phase change.