Class: Senior Secondary School 1 (SS1 / SSS1)
Term: 3rd Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Compressors: Construction of Reciprocating and Centrifugal Compressors.
Topic: Compressors Construction of compressors
Subject Matter: Screw compressor construction, rotary compressor construction, component identification

Specific Objectives

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

Cognitive Domain:

State the meaning of a compressor.
Describe the construction of a screw compressor.
Describe the construction of a rotary compressor.
Identify the main components of both screw and rotary compressors.

Affective Domain:

Appreciate the importance of compressors in refrigeration and air conditioning systems.
Show interest in learning about different types of compressors.

Psychomotor Domain:

Draw and label the key components of a screw compressor.
Draw and label the key components of a rotary compressor.

Work cooperatively in groups to identify compressor components.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology (Trade Component).
State Unified Scheme of Work for Refrigeration and Air Conditioning.
Refrigeration and Air Conditioning Technology by William C. Whitman.
https://www.racc.co.uk/compressors/screw-compressors
https://www.danfoss.com/en/products/compressors/reciprocating-compressors/

Instructional Materials

The teacher will teach this lesson with the aid of:

Actual screw compressor unit (if available)
Actual rotary compressor unit (if available)
Exploded view charts or diagrams of screw and rotary compressors

Rationale for the Lesson

This lesson helps pupils understand how different types of compressors are built and how they work. Knowing the construction of compressors is important for proper maintenance, troubleshooting, and selecting the right compressor for various applications in refrigeration and air conditioning.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of the refrigeration cycle and the general function of a compressor in a refrigeration system.

Lesson Content/Board Summary

Compressors Construction

Screw Compressor Construction

A screw compressor is a type of rotary positive-displacement compressor that uses two meshing helical screws, known as rotors, to compress gas. One rotor is typically the male rotor, and the other is the female rotor. As the rotors turn, they trap gas in pockets between the screws and the casing, reducing the volume and increasing the pressure of the gas.

The following are main components of a screw compressor:

Male Rotor
Female Rotor
Casing/Housing
Bearings
Shaft Seal
Suction Port
Discharge Port
Oil Injection System (for oil-flooded types)

Rotary Compressor Construction

A rotary compressor is a positive-displacement compressor that uses a rotating mechanism to compress gas. It typically consists of a cylindrical rotor eccentrically mounted within a larger cylinder. As the rotor turns, it traps gas between itself and the cylinder wall, compressing it before discharge.

The following are main components of a rotary compressor (rolling piston type):

Cylinder
Rotor (rolling piston)
Vane/Blade (spring-loaded)
Shaft
Suction Port
Discharge Port
Muffler
Motor

Component Identification

Identifying the components of a compressor helps in understanding its operation and maintenance. Pupils should be able to point out and name the major parts of both screw and rotary compressors from diagrams, charts, or actual units.

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 asks them to recall the function of a compressor in a refrigeration system from the previous lesson. The teacher then introduces the topic: “Compressors Construction.”
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils recall previous knowledge about compressors and are prepared for the new topic.

Step 2: Presentation of Screw Compressor Construction

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the construction and working principle of a screw compressor, using the exploded view chart or actual unit to point out the male and female rotors, casing, and other parts.
Pupils’ Activity: Pupils observe the charts/units, listen to the explanation, and ask questions for clarification.
Learning Point: Pupils understand the construction and basic operation of a screw compressor.

Step 3: Component Identification (Screw Compressor)

Time: 5 minutes
Teaching Skill: Identification/Labeling
Teacher’s Activity: The teacher guides pupils to identify and name the specific components of the screw compressor displayed on the chart or actual unit. The teacher writes the key components on the board.
Pupils’ Activity: Pupils actively participate in identifying and naming the components of the screw compressor.
Learning Point: Pupils can identify and name the parts of a screw compressor.

Step 4: Presentation of Rotary Compressor Construction

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the construction and working principle of a rotary compressor (e.g., rolling piston type), using the exploded view chart or actual unit to show the cylinder, rotor, vane, and other parts.
Pupils’ Activity: Pupils observe the charts/units, listen to the explanation, and note down important points.
Learning Point: Pupils understand the construction and basic operation of a rotary compressor.

Step 5: Component Identification (Rotary Compressor)

Time: 5 minutes
Teaching Skill: Identification/Labeling
Teacher’s Activity: The teacher guides pupils to identify and name the specific components of the rotary compressor displayed on the chart or actual unit. The teacher adds these components to the board summary.
Pupils’ Activity: Pupils identify and name the components of the rotary compressor.
Learning Point: Pupils can identify and name the parts of a rotary compressor.

Step 6: Drawing Activity

Time: 5 minutes
Teaching Skill: Practical Application
Teacher’s Activity: The teacher instructs pupils to draw a simple sketch of either a screw compressor or a rotary compressor and label its main components in their notebooks.
Pupils’ Activity: Pupils attempt to draw and label the components of a compressor.
Learning Point: Pupils apply their knowledge by visually representing compressor components.

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.
Describe the basic construction principle of a screw compressor.
List four main components of a screw compressor.
Mention three key components found in a rotary 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
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the construction and component identification of screw and rotary compressors. The teacher assigns homework: “Draw and label a simple diagram of both a screw compressor and a rotary compressor.”
Pupils’ Activity: Pupils listen to the summary, copy the board notes, and write down the homework.
Learning Point: Pupils reinforce their understanding and prepare for further study.

Lesson Keywords

Compressor – A mechanical device that increases the pressure of a gas by reducing its volume.
Screw Compressor – A rotary positive-displacement compressor that uses two meshing helical rotors to compress gas.
Rotary Compressor – A positive-displacement compressor that uses a rotating mechanism (like a rolling piston or vane) to compress gas.
Rotor – The rotating part of a compressor that traps and compresses the gas.
Vane – A movable blade used in some rotary compressors to maintain contact with the cylinder wall.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to explain the difference in operating principles between the two compressor types. For pupils needing more support, the teacher can provide pre-labeled diagrams or work closely with them during component identification.

Note for teachers using this lesson plan

It is important to have clear, large diagrams or actual compressor units for effective demonstration. Encourage pupils to actively participate in identifying components. Emphasize safety if actual units are brought into the classroom, ensuring they are de-energized and safe to handle.