Saturday, January 30, 2010

Lab Magic!

Most of us think of labs as a chance for students to practice the practical application of HVAC/R skills: brazing, charging, wiring, or troubleshooting to name a few. Certainly, students must practice their practical skills in the lab. I believe that the lab can also be instrumental in teaching more abstract concepts like gas laws or ohm’s law.

I have found that most HVAC/R students are visual and tactile learners. They learn more by seeing, touching, and doing than by reading, writing, and listening. Frequently the desire “to do” is part of what motivated them to study air conditioning in the first place, as opposed to a more academic pursuit. They arrive at the HVAC/R class excited and ready “to do”, and then we provide them with an opportunity to learn gas law formulas and ohms law. Normally we teach these subjects with an extra helping of mathematical equations. The numbers in the equations are typically all presented as part of a hypothetical example or problem. For those of us with a good understanding of the theory and the concept, the meaning is clear. For students who are still trying to understand the difference between a volt, an amp, and an ohm the problem simply becomes an exercise in math. They are not really interested in math formulas, and telling them the formulas are good for them is a bit like forcing them to take their castor oil. To overcome this, get them in the lab early and use numbers from real objects.

For ohms law, have the students measure the resistance of a strip heater, measure the voltage at the source, and then have them use ohm’s law to predict the amp draw. Next, have them operate the heater and measure its amp draw. The readings won’t be perfect, but they will be close enough to get the point across. Then do the same thing with two heaters in series and then two in parallel. They can read the individual resistance of each heater and then the combined circuit resistance to show how series and parallel resistances work. The key is to have the numbers associated with something real.

Gas behavior also works well. You can talk about the boiling point being tied to the pressure all day long and not really get the point across that boiling does not have to occur at a high temperature. This is because the information contradicts the student’s life experience – the only thing they have seen boil was hot. Put water in a flask, attach the flask to a vacuum pump, and start the vacuum pump. The water will boil at room temperature. Invite the students to touch the flask and ask questions. I have yet to see anyone who does not like this experiment. It is simple, does not take a lot of equipment, and really makes an impact.

There are many other similar labs we run whose purpose is to demonstrate an important concept. Students can quickly learn fundamental electrical circuits in the lab as well. Just make sure students know not to energize any circuits before having an instructor checks them. After the students start to connect the concepts to something that is real, then they will start to ask questions. Now you can start to use hypothetical examples and the students have a mental image of a real device to give the discussion meaning.

For some more ideas about these types of labs, take a look at the Lab Manual by David Skaves. It contains an entire section of labs labeled as Properties labs. These labs teach students about physics properties that make HVAC/R work. Although this Lab Manual is written to accompany Fundamentals of HVAC/R, it works well with any text because it is organized by subject matter with sections on Fundamentals, Properties, Refrigeration, Accessories, Controls, Electricity, Maintenance, Gas Heat, Oil Heat, and Electric Heat. Each section has several labs.

1 comment:

  1. Carter,
    Recently finished constructing a basic lab trainer that has 3 light receptacles, 3 200 watt resistors, 3 run capacitors, line voltage thermostat, transformer, switches, fan relay and an inducer. It also has 20 trouble switches installed to provide either an open, short, high resistance for troubleshooting with meters. Am BETA testing it right now to make sure the troubles do what initially I want them to do. Then will be developing a work book for students to construct series, parallel and series parallel circuits with resistors, capacitors and lamps. Measure and record voltages, resistances and amperes.

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