What IS a Grain?

Learning all the different units of measurement HVAC/R technicians must deal with can be a daunting task for students. The inability to accurately describe what you need is a major barrier to performing your job. Understanding the different units of measurement used in the HVAC/R trade simply makes your job easier. However, all of us run into specifications or terms used in technical literature that we are not really familiar with. Knowing why we use certain units for particular measurements or knowing the historical background of the units helps me remember them. Ever wondered about the origin, definition, or use of an unusual unit of measurement? Maybe even one you use often but don’t really know much about? For me, the grain had been an enigma for years. Although I used it often when working with humidity and the psychrometric chart, it was always a bit of a mystery to me. The grain is a very small unit of weight: 7000 grains equals one pound. Grains are used to measure the weight of water in each pound of dry air when working with the psychrometric chart. Grains are a perfect unit of measure for that purpose, giving us reasonable whole numbers to work with when discussing very small quantities of weight. But why the name grain, and what measurement system did this odd 7000 quantity come from? I found the answers to those questions and more at a web site called How Many? A Dictionary of Units by Russ Rowlett of the University of North Carolina at Chapel Hill. It turns out that the grain was originally based on the weight of a grain of barleycorn in England, or a grain of wheat in France. The name is literal. Many of our common measurements are based on concepts and systems that go back hundreds of years. To introduce your students to the site, ask them to look on the site and find some air conditioning specific information, like the difference between American Wire Gauge and Metric Wire Gauge, or how the American Wire Gauge came up with the particular wire diameters it uses. Here is another challenge: how many of you know what the gauge of a shotgun is based on? To find out go to Mr. Rowlett’s site, How Many? A Dictionary of Units. However, I warn you that you can get lost for hours reading the intriguing background to common measurements.

The Formula To Success

A problem that many students have when beginning their study of air conditioning and refrigeration is that many of the most crucial concepts are traditionally presented primarily through math formulas. Even simple concepts become confusing when they are presented using traditional algebraic formulas that assign constants and variables for each measurement. For many students, algebraic explanations become barriers to learning. Presenting the foundation science conceptually and using analogies to common life experiences helps. If students understand the basic idea, learning the math that represents the idea is easier. That is why Fundamentals of HVAC/R presents science facts conceptually, not just as math formulas.

Take gas laws for example. Relate temperature to the average speed of the molecules: higher temperatures produce faster moving molecules; lower temperatures produce slower moving molecules. Next tell students to imagine gas pressure as the force of the gas molecules colliding with the sides of the container holding them. The more collisions produce higher gas pressure; fewer collisions produce lower gas pressure. Now tie the two concepts together: when a gas is heated the molecules move faster, increasing collisions with the sides of the container which increases the gas pressure. When a gas is cooled the molecules move slower, reducing collisions with the sides of the container which reduces the gas pressure. Discuss this point and ask questions to make sure they understand. After they have grasped the pressure temperature relationship you can introduce the related formula. Understanding the concept first makes the math a little easier to grasp because they have some context to hang it on. Remember it is more important for students to understand the pressure-temperature relationship than it is for them to calculate gas law formulas. Being able to work the gas law formula is not really the goal, understanding the temperature-pressure relationship is.

However, most standardized tests in this filed still rely heavily on manipulating traditional math formulas. So we also discuss common formulas that students are likely to see in HVAC/R literature and standardized tests, like the ICE or NATE. Throughout the book, whenever a formula is introduced, we give detailed examples showing step by step how the formula is used. To make the example formulas are easy to follow they are presented in the most straight forward, uncomplicated way possible. The text also uses practical examples showing the usefulness of the formulas that are introduced. Students are more willing to make an effort learning something that has a demonstrated application. Besides discussing formulas throughout the text whenever they are relevant, Fundamentals of HVAC/R lists many useful formulas in one place: Appendix B Commonly Used HVAC/R Formulas.

A good exercise in preparation for taking an industry standardized test is for the students to look through all the formulas listed in Appendix B and make certain they understand how to apply each formula. The unit in the text where the formula is discussed is listed beside each formula. This shows students where to look for a discussion and an example problem for any particular HVAC/R formula.

Teaching the Virtual Generation

Do you have students from the “virtual generation”? These are young people who are very bright, have great hand-eye coordination, but have never used a wrench because an increasing amount of their existence is online. They talk with their friends, do research, play games, and generally “live” online for a large part of their time. Studies have suggested that this actually improves their mental agility and problem solving skills, both valuable assets for service technicians. Unfortunately, their exposure and experience with real life tools and mechanics is limited to non-existent. HVAC/R mechanics rely on their tools for survival. It is not possible to install, service, or troubleshoot HVAC/R systems without tools. Having the correct tools for the job and knowing how to use them can be the difference between success and failure. That is why Fundamentals of HVAC/R devotes an entire section of the book to tools. The units in the Tools and Equipment section are:

Unit 9 Hand and Power Tools
Unit 10 Screws, Rivets, Staples, and Other Fasteners
Unit 11 Electrical Measuring and Testing Meters
Unit 12 Refrigerant System Servicing and Testing Equipment
Unit 13 Heating system Servicing and Testing Equipment
Unit 14 Calibration of Meters and Instruments

These units provide an overview of the tools used by technicians who perform HVAC/R work. The units are filled with high quality, full color photographs of the tools and equipment. These units not only show the tools, but also provide illustrations and descriptions showing how the tools are used. This is particularly important for more unusual tools. For example, the use of a duct stretcher is shown in Unit 9. Yes, there really is a tool called a duct stretcher!

One student confessed to me after he graduated that he had never held a wrench until he took my Air Conditioning class. What he didn’t know was that it was fairly obvious. The good news is that his innate intelligence and strong work ethic allowed him to overcome this and go on to be successful. We gave him lots of shop projects requiring tool use. We monitored, corrected, demonstrated, and advised as he progressed towards tool competence.

Before he graduated he took a job as a helper for one of the best refrigeration mechanics in town, who also happens to be a patient man. You see, the mechanic had cancer, and his ability to perform the physical part of the job was declining. The student became the hands and arms for a gifted mechanic. In the course of a summer became proficient at using tools. He has now been with that company for two years and loves his job and the people he works with. If you have bright eyed, eager students from the “virtual generation” show them how to hold a wrench, give them lots of shop work to practice their tool use, and be patient with them. They could end up working with the best mechanic in town.

It's Called a Compressor Because ..

How often have your students asked for study guides and hints before tests? Tell them that the hints are built into the terminology. In many cases, HVAC/R terms define themselves. The names for most components and processes are not randomly chosen, they are frequently drawn from general vocabulary to describe a component or process. For example, a compressor compresses gas. The word compress means to make smaller. When you squeeze something you make it smaller, or compress it. The compressor raises the pressure and temperature of the gas by squeezing it, making its volume smaller. If the students understand that compress means to squeeze, they should have no trouble remembering what the compressor does.

To truly understand HVAC/R terminology students should not simply memorize a list of attributes for the rather large number of HVAC/R terms, but should connect the function to the name. Making these connections also increases memory retention. The method that a compressor uses to accomplish its work is used to describe the types of compressors. Reciprocate means to go back and forth: a reciprocating compressor uses pistons that go back and forth in a cylinder. A scroll is spiral: scroll compressors use intermeshing spirals or scrolls to compress the gas. A screw compressor uses intermeshing auger shaped screws to compress the gas. Connecting the name to the function will help students get a mental picture of the device and increase both understanding and memory retention.

All the components of the refrigeration cycle have names that either describe their function or describe them physically. The key is for students to understand where the name comes from. If students understand that orifice is simply a three syllable word for hole, they should have not problem remembering what an orifice is. One of the reasons I believe in covering the science behind the refrigeration cycle before trying to discus the refrigeration cycle is so that these connections can be made. If the students already understand the processes of evaporation and condensation, they will have no trouble remembering what evaporators and condensers do. This same technique can be used for many aspects of HVAC/R. In electricity potential difference literally means the difference in electrical potential between two points. The refrigerant terms zeotropic and azeotropic can be better understood if you explain the vocabulary they are built on. For most of us, these words are presented simply as arcane terms for refrigerants that are mixtures of two or more refrigerants. The fact that they differ by a single letter makes remembering the difference between the two difficult. Most students complain that the two terms are “all Greek to me!” In fact they do come from Greek roots. “Zeo” is to boil, “trop” is to turn, so zeotropic refrigerants turn, or change as they boil. Placing the letter “a” in front means “not.” For example: amoral means without morals. Similarly, azeotropic refrigerants do NOT turn or change when they boil. Give a few vocabulary lessons and increase your student’s understanding and memory retention. For more HVAC/R vocabulary tips check out the glossary in Fundamentals of HVAC/R, the largest glossary in any major HVAC/R text.

Combustion Air

The arrival of fall brings the start of gas and oil fired furnace seasonal checks. An easily overlooked problem with gas and oil furnaces is lack of combustion air. Although most technicians understand the necessity of adequate combustion air, it is easily overlooked if technicians view their job as servicing appliances rather than systems. Most school shops have no combustion air issues because they are typically great big leaky rooms. On the other hand, the newer homes your students are likely to see are typically very tight, requiring installers and service technicians to be conscious of the need for combustion air. I believe we should stress the consequences of inadequate combustion air. Most students understand that air is required for combustion and that new air must constantly be brought in to replace the air that was just used in the combustion process. They should also understand that the carbon and hydrogen in the fuel are combining with the oxygen to make carbon dioxide and water, the normal products of complete combustion. You can then explain that if there is not enough oxygen, carbon monoxide and unburned carbon will start to form because there is not enough oxygen to complete the combustion process. In a room with inadequate combustion air, as the combustion process continues the pressure in the room becomes negative, reducing the effectiveness of the vent. In bad cases the combustion products can start to spill out of the vent. Now you have a scary situation: a combustion process producing carbon monoxide and combustion gasses spilling out into the room! I have heard of cases where smoke from fireplaces in newer homes comes rolling out into the room when the furnace comes on because the house simply does not have enough combustion air for both the fireplace and the furnace. Technicians should look for combustion air grills and vents when servicing furnaces. Typically there should be an opening or grille near the ceiling and another near the floor. If the grille opens directly to the outside the free area of the grille should be at least one square inch for every 4,000 Btuh of combined input rating. If the combustion air must travel through vertical ducts the ducts must also have a free area of at least one square inch for every 4,000 Btuh. If the air must travel through horizontal ducts, the grille and the ducts must be larger. They must have a free area of at least one square inch per 2,000 Btuh. Draft measurements and room pressurization measurements can tip off technicians to combustion air problems. Because a draft gauge measures the vent pressure relative to the room pressure, inadequate combustion air will cause the draft reading to decrease the longer the furnace operates. An absolute pressure reading of the room will show that the room pressure is decreasing as the furnace continues to operate without adequate combustion air. A quick test is to introduce more combustion air near the furnace by opening a window or door to the outside. If the draft increases when the window is opened and decreases again when it is closed, the room needs more combustion air. For more a more detailed discussion of combustion air check out Unit 37 Gas Fired Heating Systems, Unit 40 Gas Furnace Installation, Startup, Checkout and Operation, Unit 41 Troubleshooting Gas Furnaces, and Unit 44 Residential Oil Heating Installation in the text Fundamentals of HVAC/R.