2.0.1 — General Learning Outcomes

Upon successful completion of this section, the apprentice will be able to:

• Distinguish between sensible heat and latent heat and explain how each affects temperature and moisture levels in HVAC/R systems.
• Describe the heating curve of water and identify what is happening at each stage as heat is added from ice through to superheated steam.
• State the latent heat of fusion and latent heat of vaporization of water in both Imperial and SI units, and explain their significance.
• Explain the difference between evaporation and boiling, define dew point, and describe how condensation on an evaporator coil removes moisture from air.
• Describe how pressure affects the boiling point of a liquid and explain why this principle enables mechanical refrigeration.

2.0.2 — Section 2 — Lessons at a Glance

Section 2 builds from the concept of heat as energy, through the mechanics of phase change, all the way to the pressure–temperature relationship that makes refrigerants work. Each lesson builds on the previous one.

2.0.3 — Key Terms — Section 2 Preview

These terms appear throughout Section 2 and connect directly to Section 3 (Pressure–Temperature Relationship) and Section 4 (Vapour Compression Cycle).

2.0.4 — Why Phase Transition Matters in HVAC/R

Refrigeration does not create cold — it moves heat. And the most efficient way to move large amounts of heat is to exploit phase change. When a refrigerant changes from liquid to vapour, it absorbs an enormous amount of heat without its temperature rising. When it changes back from vapour to liquid, it releases that same heat.