Have you ever noticed that the more you're required to speed up to get all your work done in a day, the more the cleanliness of your work vehicle suffers?

Some techs won't clean their vans, no matter how slow or busy the schedule gets, but most of us prefer a clean and organized vehicle. However, our van cleanliness can slip a bit in the really busy season.

This is entropy at work.

One way to think of entropy is the tendency for energy to be “wasted” or for energy to become more disorganized as it is changed from one form to another. In practical terms, the higher the entropy, the greater the waste in moving energy around. The lower the entropy, the less energy is wasted or unusable.

When your van is clean, you waste less energy trying to find what you need, but that is easier to do when you aren't “rushed.”

Don't confuse entropy with enthalpy. Entropy is the measure of the “availability” of energy to do useful work; enthalpy is a measure of total heat content.

Alternatively, you can think of entropy as the tendency for everything to go from more organized to less organized over time.

When we talk about entropy in classroom settings, we typically do it when analyzing a pressure-enthalpy diagram of a refrigeration circuit like the one shown above. You will notice the red shape is nearly a rectangle, barring the slanted line on the right; that line shows what happens when the refrigerant is compressed. Rather than going straight up and down, it curves to the right to show that additional heat is added to the refrigerant (enthalpy) as it is compressed. This increase in enthalpy follows something called lines of constant entropy; in other words, as more energy is added to a system, the faster the molecules move and the less organized they become.

As pressure and temperature increase, so (generally) does entropy. When it gets hot and the dispatcher starts putting pressure on you, your van entropy also increases.

In a refrigeration circuit, the system will work more efficiently when we achieve the desired movement of BTUs with a minimal amount of entropy. Practically speaking, this means using lower pressures and temperatures to move heat from one place to another when possible, but we still need to get the job of moving heat from one place to another done. In that process, entropy WILL occur.

We all know the guy who has the PERFECT van, the spotless tools, and the clean uniform. His van stays that way because he hardly does anything, and then he takes 20 minutes after every call, wiping down and oiling his tools. He has very little entropy in his van because there is very little WORK being done.

Absolute zero is the temperature at which no molecular motion exists. In that state, there is also no entropy. No heat, no work, no disorganization. More heat, more work, more disorganization (entropy).

So, don't use me as an excuse for a messy van, but if your boss hassles you too much on a busy day, you can remind him of what we discussed today. Heat and pressure result in entropy, and the back of that van—that's entropy, baby.

—Bryan

P.S. – I know that this article took some liberty with definitions. It's an analogy, not a science textbook. You can find another explanation of entropy HERE.