Refrigeration Components, Functions and Accessories for SS 3

Class: SSS 3
Term: First Term
Week: 6
Age: 16 years
Duration: 45 minutes
Subject: Refrigeration and Air Conditioning
Curriculum Theme: Refrigeration and Air Conditioning
Previous Lesson:
Topic: Forms of refrigeration
Subject Matter: Function of the components and accessories e.g. relays, solenoid valves, capacitors, thermostats etc of absorption system of refrigeration

Specific Objectives

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

Cognitive Domain

• Identify common components and accessories used in refrigeration systems.
• State the function of relays in an absorption refrigeration system.
• Describe the function of solenoid valves in an absorption refrigeration system.
• Explain the role of capacitors in an absorption refrigeration system.
• Outline the function of thermostats in an absorption refrigeration system.

Affective Domain

• Appreciate the importance of each component for the proper functioning of an absorption refrigeration system.
• Show interest in learning about different refrigeration system components.

Psychomotor Domain

• Draw simple diagrams illustrating the placement of these components in an absorption system.
• Demonstrate how a thermostat controls temperature in a simulated absorption system setup.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Refrigeration and Air Conditioning Technology textbook for SS 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Diagrams of absorption refrigeration systems
• Pictures or actual samples of relays, solenoid valves, capacitors, and thermostats
• Whiteboard and markers

Rationale for the Lesson

Understanding the function of various components and accessories is fundamental to comprehending how refrigeration systems operate and for effective troubleshooting. This lesson provides students with essential knowledge about the control elements in an absorption refrigeration system, which is crucial for practical applications and further studies in refrigeration and air conditioning technology.

Prerequisite/Previous Knowledge

Students should have a basic understanding of the principles of refrigeration and the general concept of an absorption refrigeration system.

Lesson Content/Board Summary

Refrigeration Components, Functions and Accessories

Understanding Absorption Refrigeration Systems

An absorption refrigeration system uses a heat source (like natural gas, steam, or solar energy) to drive the refrigeration cycle, rather than a mechanical compressor. It typically uses a refrigerant (e.g., ammonia) and an absorbent (e.g., water). While distinct from vapour compression, it still requires various components and accessories for control, safety, and efficient operation.

Key Components and Their Functions

Relays

Relays are electrical switches that open and close circuits in response to electrical signals. In an absorption refrigeration system, relays can be used to:

1. Control auxiliary electrical loads such as circulation pumps (if electrically driven) that move the solution between the absorber and generator.
2. Switch on or off electric heating elements that might be used as the heat source for the generator.
3. Control fans for air-cooled condensers or absorbers, based on temperature or pressure signals.

Solenoid Valves

Solenoid valves are electromechanically operated valves that control the flow of fluids (liquids or gases) in a refrigeration system. In absorption systems, they are often used to:

1. Regulate the flow of refrigerant or absorbent solution to maintain optimal operating conditions.
2. Control the flow of cooling water to the absorber or condenser.
3. Act as shut-off valves in various parts of the system for maintenance or safety.
4. Manage the flow of the heat source (e.g., gas supply to a burner) to control the generator’s heat input.

Capacitors

Capacitors are electrical components that store electrical energy in an electric field. While more prominent in vapour compression systems for compressor motors, in absorption systems, capacitors may be found:

1. As starting or running capacitors for electric motors that drive circulation pumps.
2. In control circuits to filter electrical noise or provide timing functions for specific operations.
3. For power factor correction in systems with significant electrical loads.

Thermostats

Thermostats are temperature-sensing devices that maintain a desired temperature by controlling the operation of the refrigeration system. In an absorption system, a thermostat typically:

1. Senses the temperature of the refrigerated space or the cooling medium.
2. Sends a signal to control the heat input to the generator (e.g., by actuating a solenoid valve on a gas line or controlling an electric heater).
3. Can also control auxiliary components like fans or pumps to maintain the desired temperature range.

Teaching Methods/Instructional Techniques

Discussion, Explanation, Question and Answer, Demonstration, Visual Aids.

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Review/Engagement

Teacher’s Activity: The teacher greets the students and briefly reviews the concept of an absorption refrigeration system, asking students to recall its main components (generator, condenser, evaporator, absorber). The teacher then introduces the day’s topic: the functions of specific components and accessories.

Pupils’ Activity: Students respond to questions and listen attentively to the introduction.

Learning Point: Absorption system recall

Step 2: Introduction to Relays

Time: 7 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains what a relay is, showing a diagram or actual sample. The teacher then explains its function in an absorption refrigeration system, focusing on controlling electrical loads like pumps or heaters.

Pupils’ Activity: Students observe the diagrams/samples and listen to the explanation, asking questions for clarity.

Learning Point: Relay function explained

Step 3: Understanding Solenoid Valves

Time: 7 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher introduces solenoid valves, showing diagrams or a sample. The teacher explains their function in controlling fluid flow (refrigerant, solution, water, or heat source) within an absorption system.

Pupils’ Activity: Students observe and listen, relating the explanation to the system’s operation.

Learning Point: Solenoid valve function

Step 4: Role of Capacitors

Time: 7 minutes

Teaching Skill: Explanation/Clarification

Teacher’s Activity: The teacher explains the basic principle of a capacitor and details its potential roles in an absorption system, particularly in relation to motor starting/running for pumps or fans, and in control circuits.

Pupils’ Activity: Students listen and try to understand the electrical aspect of the components.

Learning Point: Capacitor role in system

Step 5: Function of Thermostats

Time: 7 minutes

Teaching Skill: Explanation/Application

Teacher’s Activity: The teacher explains the function of a thermostat as a temperature control device. The teacher describes how it senses temperature and controls the operation of the absorption system, for example, by regulating the heat input to the generator.

Pupils’ Activity: Students listen and connect the thermostat’s function to maintaining desired temperatures.

Learning Point: Thermostat temperature control

Step 6: Discussion and Reinforcement

Time: 4 minutes

Teaching Skill: Question and Answer

Teacher’s Activity: The teacher facilitates a brief discussion, asking students to summarise the function of each component and how they work together in an absorption system. The teacher clarifies any misconceptions.

Pupils’ Activity: Students participate in the discussion, answering questions and reinforcing their understanding.

Learning Point: Component interrelationship

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

1. What is the primary function of a relay in an absorption system?
2. How do solenoid valves contribute to the control of an absorption refrigeration system?
3. Mention one specific use of a capacitor in an absorption refrigeration system.
4. Explain how a thermostat helps in maintaining temperature in an absorption system.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Component function assessment

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on the functions of refrigeration components and accessories into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Notes on component functions

Step 9: Conclusion

Time: 1 minute

Teaching Skill: Summarisation

Teacher’s Activity: The teacher briefly summarises the importance of understanding the functions of relays, solenoid valves, capacitors, and thermostats for the effective operation and maintenance of absorption refrigeration systems.

Pupils’ Activity: Students listen and reflect on the lesson.

Learning Point: Lesson consolidation

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook.

1. Differentiate between the function of a relay and a solenoid valve in a refrigeration system.
2. Research and list two other accessories that might be found in a complex absorption refrigeration system and describe their functions.
3. Draw a simple block diagram of an absorption refrigeration system and indicate where a thermostat and a solenoid valve would typically be placed.

Lesson Keywords

• Relay – An electrical switch that controls a circuit by opening or closing contacts.
• Solenoid Valve – An electromechanical valve used to control the flow of fluid or gas.
• Capacitor – An electrical component that stores and releases electrical energy.
• Thermostat – A device that senses temperature and controls a heating or cooling system to maintain a desired temperature.
• Absorption System – A refrigeration system that uses a heat source to drive the cooling cycle, without a mechanical compressor.

Differentiation

For weaker learners, provide simplified diagrams and focus on identifying each component and stating its primary function. For faster learners, encourage them to research specific types of relays or solenoid valves and their applications in different absorption system designs, or to explore how these components interact in a control loop.

Suggested Lesson Videos

For further understanding, search on YouTube for: “Functions of refrigeration components absorption system” or “How absorption chillers work components”.

Teacher Guide for Using This Lesson Plan

Before the lesson, gather clear diagrams or actual samples of relays, solenoid valves, capacitors, and thermostats. Prepare the whiteboard with a basic outline of an absorption refrigeration system to help students visualize where these components fit. Begin by reviewing the core principles of absorption refrigeration to set the context. Explain each component’s function clearly, providing practical examples relevant to an absorption system. Encourage questions and facilitate a brief discussion to check understanding after each component is introduced. During Step 7, ensure questions are direct and assess knowledge of the specific functions taught. Guide students to copy the Board Summary notes accurately in Step 8. For practical application, you might briefly discuss common faults associated with these components if time permits, ensuring safety is always paramount when discussing electrical components.