A problem that many students have when beginning their study of the refrigeration cycle is the large number of technical terms and new concepts used to describe what happens in the refrigeration cycle. For many students, grasping all of this information at once is simply information overload. Many students turn to rote memory in order to recite all that happens to the refrigerant in the refrigeration cycle. However, if students don’t really understand the basic science behind the concepts and terminology, the information is just a collection of seemingly random facts that must be memorized, like the multiplication tables. There is no doubt that some memorizing of new terms is necessary, but I believe an understanding of the concepts and terms helps students remember them. Understanding the science behind the cycle also helps them keep the cycle details straight. In Fundamentals of HVAC/R, we promote this understanding by devoting section two of the book to HVAC/R Science. Units 4 through 8 explain the science that makes HVAC/R systems work. Because this is an Air Conditioning text, the principles are presented using plain language with a minimum of mathematical formulas. The practical application of the science concepts to refrigeration is explained when the concepts are introduced. The goal is to give students the conceptual tools they need to really understand the refrigeration cycle.
Unit 4 Properties of Matter explains what matter is, basic atomic structure, and the most important properties of matter. These include the three common states of matter, density and specific gravity, change of state, the effect of pressure on boiling and condensing. Unit 5 Types of Energy and Their Properties explains the relationship between matter, energy, work, and power. Types of energy and conversion from one form to another are discussed. Common units for measuring both power and work in the HVAC/R trade are discussed and compared. Unit 6 Temperature Measurement and Conversion logically follows the unit on energy. The four common temperature scales are discussed along with a discussion of absolute zero and absolute temperature. A brief history of thermometers and temperature measurement adds interest to what can be a dry subject. How to take accurate temperature readings with different types of thermometers is also discussed in detail. Unit 7 Thermodynamics – The Study of Heat explores heat methods of transfer, sensible and latent heat, and specific heat capacity. The way both sensible and latent heat are used in the refrigeration cycle is also discussed. This unit explains how to use PT charts and discusses the difference between saturated mixtures, a superheated gases, and subcooled liquids. Unit 8 Pressure and Vacuum covers what pressure and vacuum are and how they are measured. Atmospheric pressure and the difference between gauge and absolute pressure are discussed in detail. Different pressure measurement systems such as psia, psig, inches of mercury and inches of water are discussed. The unit closes with coverage of the gas laws. Illustrations and examples show graphically how the gas laws work and how they help make the refrigeration cycle work.
Although the concepts are not discussed primarily in terms of math formulas, the most important formulas associated with these concepts are presented. Whenever a formula is introduced, we give detailed examples showing step by step how the formula is used. Students will have no trouble following the formula examples because they are presented in the most straight forward, uncomplicated way possible.
I believe that students save time in the long run by taking time at the beginning to understand the science that makes HVAC/R systems work. By the time students complete units 4 through 8, they have a good grasp of all the concepts necessary to understand the refrigeration cycle.