Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: Second Term
Week: 9
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Refrigerants: Definition of Refrigerants and Functions.
Topic: Refrigerants
Subject Matter: Types of refrigerants, natural refrigerants, synthetic refrigerants

Specific Objectives

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

Cognitive Domain:

Define refrigerants.
List the two main categories of refrigerants.
State examples of natural refrigerants.
Identify different types of synthetic refrigerants (CFCs, HCFCs, HFCs, HFOs).
Differentiate between natural and synthetic refrigerants.

Affective Domain:

Appreciate the importance of selecting environmentally friendly refrigerants.
Recognize the need for safe handling of refrigerants.

Psychomotor Domain:

Identify common refrigerant types from their labels or cylinders (if available).

Discuss the environmental implications of using certain refrigerants.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (Senior Secondary)
State Unified Scheme of Work (Refrigeration and Air Conditioning)
Refrigeration and Air Conditioning Technology Textbook

Instructional Materials

The teacher will teach this lesson with the aid of:

Gas cylinders (empty, for demonstration)
Refrigerant labels
Safety charts showing refrigerant properties

Rationale for the Lesson

Understanding different types of refrigerants is important for pupils because it helps them know how cooling systems work. This knowledge also enables them to understand the environmental effects of various refrigerants and the need for proper selection and handling in their daily lives and future careers.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of cooling and heating principles.

Lesson Content/Board Summary

Types of Refrigerants

What are Refrigerants?

Refrigerants are substances, usually fluids, that absorb heat from one area and release it into another, causing cooling. They are used in refrigerators, freezers, and air conditioners.

Classification of Refrigerants

Refrigerants are broadly classified into two main categories based on their origin and chemical composition:

Natural Refrigerants
Synthetic Refrigerants

Natural Refrigerants

Natural refrigerants are substances that occur naturally in the environment or are produced through natural processes. They have low environmental impact and are often non-toxic or have low toxicity.

Examples of natural refrigerants include:

Ammonia (NH3): Known for its high efficiency but is toxic and flammable.
Carbon Dioxide (CO2): Non-toxic, non-flammable, but operates at very high pressures.
Hydrocarbons (HCs): Such as Propane (R290) and Isobutane (R600a). They are flammable but have very low global warming potential (GWP).
Water (H2O): Used in some large-scale absorption chillers.

Synthetic Refrigerants

Synthetic refrigerants are man-made chemical compounds developed for refrigeration and air conditioning applications. They were developed to overcome some limitations of natural refrigerants, such as toxicity or flammability.

Synthetic refrigerants are further grouped based on their chemical structure and environmental impact:

Chlorofluorocarbons (CFCs): These contain chlorine, fluorine, and carbon. They have high ozone depletion potential (ODP) and global warming potential (GWP). Examples include R11, R12. Their production is largely phased out due to environmental concerns.
Hydrochlorofluorocarbons (HCFCs): These contain hydrogen, chlorine, fluorine, and carbon. They have lower ODP than CFCs but still contribute to ozone depletion. Examples include R22. Their production is also being phased out.
Hydrofluorocarbons (HFCs): These contain hydrogen, fluorine, and carbon. They do not contain chlorine, so they have zero ODP. However, many HFCs have high GWP, contributing to climate change. Examples include R134a, R410A. Efforts are being made to reduce their use.
Hydrofluoroolefins (HFOs): These are newer synthetic refrigerants with very low GWP and zero ODP. Examples include R1234yf. They are considered a more environmentally friendly alternative to HFCs.

Key properties of synthetic refrigerants often considered are:

Ozone Depletion Potential (ODP): A measure of how much a chemical can deplete the ozone layer.
Global Warming Potential (GWP): A measure of how much a given mass of a chemical contributes to global warming compared to the same mass of carbon dioxide over a specific period.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 3 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher asks pupils what makes their refrigerators or air conditioners cold. The teacher then introduces the topic: “Refrigerants and their Types.”
Pupils’ Activity: Pupils respond to the questions and listen attentively.
Learning Point: Pupils are prepared for the lesson and understand the topic for the day.

Step 2: Explanation of Refrigerants and Classification

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines what refrigerants are and introduces the two main categories: natural and synthetic refrigerants. The teacher writes these points on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and broad classification of refrigerants.

Step 3: Natural Refrigerants

Time: 8 minutes
Teaching Skill: Elucidation/Listing
Teacher’s Activity: The teacher explains what natural refrigerants are, provides examples like Ammonia, Carbon Dioxide, and Hydrocarbons, and discusses their general properties (e.g., toxicity, flammability, environmental impact).
Pupils’ Activity: Pupils listen, observe examples, and write down key points.
Learning Point: Pupils learn about natural refrigerants and their characteristics.

Step 4: Synthetic Refrigerants

Time: 8 minutes
Teaching Skill: Explanation/Categorisation
Teacher’s Activity: The teacher explains what synthetic refrigerants are and discusses their different types: CFCs, HCFCs, HFCs, and HFOs. The teacher highlights the environmental concerns associated with each type, such as Ozone Depletion Potential (ODP) and Global Warming Potential (GWP).
Pupils’ Activity: Pupils listen, ask questions about environmental impact, and take notes.
Learning Point: Pupils understand synthetic refrigerants and their environmental implications.

Step 5: Discussion and Identification

Time: 9 minutes
Teaching Skill: Demonstration/Discussion
Teacher’s Activity: The teacher displays various refrigerant labels or empty gas cylinders and guides pupils to identify the type of refrigerant. The teacher facilitates a discussion on the importance of choosing environmentally friendly refrigerants and safe handling practices.
Pupils’ Activity: Pupils observe the materials, identify refrigerant types, participate in the discussion, and share their views on environmental responsibility.
Learning Point: Pupils can identify common refrigerants and appreciate the need for responsible use.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define refrigerant.
Mention two main categories of refrigerants.
List two examples of natural refrigerants.
State three types of synthetic refrigerants and explain one environmental concern associated with them.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of understanding refrigerant types and their environmental impact. The teacher assigns homework: “Research one new environmentally friendly refrigerant and write a short paragraph about its advantages.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils recall the main aspects of the lesson and are given further engagement.

Lesson Keywords

Refrigerant – A substance used in a refrigeration cycle, which undergoes phase changes to absorb and release heat.
Natural Refrigerant – Substances found in nature or produced by natural processes, used for cooling.
Synthetic Refrigerant – Man-made chemical compounds used for refrigeration.
CFC (Chlorofluorocarbon) – A type of synthetic refrigerant with high ozone depletion potential.
HCFC (Hydrochlorofluorocarbon) – A type of synthetic refrigerant with lower ozone depletion potential than CFCs.
HFC (Hydrofluorocarbon) – A type of synthetic refrigerant with zero ozone depletion potential but high global warming potential.
HFO (Hydrofluoroolefin) – A newer type of synthetic refrigerant with very low global warming potential and zero ozone depletion potential.
ODP (Ozone Depletion Potential) – A measure of how much a chemical can deplete the ozone layer.
GWP (Global Warming Potential) – A measure of how much a chemical contributes to global warming.
Ammonia – A natural refrigerant (NH3), efficient but toxic and flammable.
Propane – A natural hydrocarbon refrigerant (R290), flammable with low GWP.
Carbon Dioxide – A natural refrigerant (CO2), non-toxic but operates at high pressures.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research specific applications of different refrigerant types. For pupils needing more support, the teacher can provide simplified diagrams of refrigerant classification and focus on identifying the two main categories and their common examples.

Note for teachers using this lesson plan

Ensure that any gas cylinders or refrigerant labels used for demonstration are empty and safe to handle. Emphasize the safety precautions required when working with actual refrigerants. Encourage pupils to ask questions, especially regarding the environmental aspects, to foster critical thinking.