This chapter focuses on producing geometric drawings essential for Refrigeration and Air Conditioning (RAC) professionals in Kenya. Accurate geometric drawings serve as the foundation for designing, fabricating, installing, and maintaining refrigeration and air conditioning systems. Mastery of line types used in these drawings is critical for clear communication of technical details and specifications among engineers, technicians, and contractors.

2.1 Types of lines in drawings

In the field of Refrigeration and Air Conditioning, geometric drawings use standardized line types to represent various features such as visible edges, hidden components, center lines, and cutting planes. Understanding these line types ensures that designs are interpreted correctly and installations proceed without costly errors or delays. Kenyan RAC professionals regularly create and read drawings for ductwork, piping, component layout, and equipment placement, making fluency in line types indispensable.

2.1.1 Continuous thick lines (Visible lines)

Continuous thick lines represent edges and outlines of objects that are visible in the current view. These lines define the actual shape and boundaries of components such as compressors, condensers, evaporators, and piping in RAC drawings.

Governing concept:

Continuous thick lines clearly show the parts of an object that would be seen by an observer from a particular viewpoint. They are the most prominent lines in a drawing.

Line specification:

• Thickness typically ranges from 0.7 mm to 1.0 mm on printed drawings.
• No breaks or gaps along the line.
• Used to depict edges, outlines, and surfaces visible in the view.

Worked Examples

Example 1:
Given a refrigeration compressor outline represented by a rectangle 200 mm wide and 150 mm high, draw the visible edges using continuous thick lines.

Example 2:
A duct section measuring 300 mm by 400 mm is shown in elevation. Represent the visible edges using continuous thick lines of 0.8 mm thickness.

Example 3:
Draw the visible outline of an evaporator coil with a circular cross-section of diameter 500 mm using continuous thick lines.

2.1.2 Dashed lines (Hidden lines)

Dashed lines represent edges or boundaries that are not visible from the current viewpoint because they are obscured by other parts of the object. In RAC drawings, hidden lines indicate internal features such as pipe interiors, internal fins, or mounting holes.

Governing concept:

Dashed lines communicate the presence of features behind or inside visible surfaces, allowing technicians to understand the full structure without additional views.

Line specification:

• Consist of short dashes approximately 3 mm long separated by 1.5 mm gaps.
• Thickness is thinner than continuous thick lines, typically 0.35 mm to 0.5 mm.
• Used for hidden edges, internal components, and features behind visible surfaces.

Worked Examples

Example 1:
A refrigeration pipe passes behind a wall. The visible wall outline is drawn with continuous thick lines. Represent the hidden pipe behind the wall with dashed lines.

Example 2:
In a sectional view of an air conditioning unit, internal fins are not visible externally. Draw the hidden fins using dashed lines.

Example 3:
A mounting bracket with holes is shown from the front. The holes are behind the front surface. Represent these holes with dashed lines.

2.1.3 Chain lines (Center lines and cutting planes)

Chain lines consist of alternating long and short dashes and are used to indicate the center axes of symmetrical objects or cutting planes for sectional views. In RAC drawings, chain lines mark the center of cylindrical pipes, ducts, or rotating shafts.

Governing concept:

Center lines provide reference for symmetry, alignment, and positioning, essential for accurate fabrication and installation. Cutting plane lines indicate where an object is sliced to show internal details.

Line specification:

• Consist of a pattern of one long dash (6 mm) followed by a short dash (2 mm).
• Thickness usually similar to dashed lines (0.35 mm to 0.5 mm).
• Often terminated with arrows for cutting planes.

Worked Examples

Example 1:
Draw the center line of a cylindrical refrigeration pipe 100 mm diameter.

Example 2:
Indicate the cutting plane for a sectional view through an air conditioning evaporator coil.

Example 3:
Mark the center line of a rectangular duct 500 mm by 300 mm.

2.1.4 Phantom lines (Alternate positions and adjacent parts)

Phantom lines are used to show alternate positions of moving parts, adjacent components, or repeated details. They help illustrate the range of motion or spatial relationships in RAC assemblies.

Governing concept:

Phantom lines communicate optional or non-permanent states of components without cluttering the main drawing with extra views.

Line specification:

• Comprise a repeating pattern of one long dash (6 mm) followed by two short dashes (1.5 mm each).
• Thickness similar to dashed lines.
• Used sparingly to avoid confusion.

Worked Examples

Example 1:
Show the alternate position of a valve handle in a refrigeration system using phantom lines.

Example 2:
Illustrate the range of motion of a sliding damper in an air conditioning duct.

Example 3:
Represent adjacent piping arrangement relative to a main pipe using phantom lines.

Chapter Summary

This chapter covered essential aspects of producing geometric drawings, starting with the various types of lines used in technical drawings, each serving a distinct purpose for clarity and communication. It then explored the methods for constructing basic geometric forms such as circles, triangles, and polygons, providing a foundation for more complex designs. The chapter proceeded to detail the construction of different angles, emphasizing accuracy and precision in drawing. Techniques for measuring angles were also discussed, highlighting the tools and procedures necessary for correct angle determination. Additionally, the chapter explained how to bisect angles and lines, an important skill for dividing elements evenly in a drawing. Finally, it addressed standard drawing conventions that ensure consistency and universal understanding in technical drawings, reinforcing the importance of adhering to these norms in professional practice.