HVAC Training – Laws of Thermodynamics

by Ron Walker

To understand how refrigeration and air conditioning systems work, you must first know the laws of thermodynamics as they pertain to refrigeration. You could study thermodynamics for weeks on end, but I will try to break it down to what you need to know as they apply to refrigeration.

Law 1 – There is no such thing as cold.

All of our lives we’ve talked about cold. As an air conditioning technician you must start to think in terms of heat (believe me, it will make things much easier when you learn about heat pumps). So, -20F is what most people would consider cold. But if you consider that absolute zero is -460F, then you can see the between cold (no heat) and -20 there is 440F.  These 440F are heat.

Think of it this way. The refrigerator in your kitchen, does not add cold, it removes heat. It is designed to remove heat faster than heat can seep in through the box.

Law 2 – Heat energy flows towards anything that contains less heat. Some would say from hot to cold, but let’s keep it from heat to less heat.

Let’s take two equal size pieces of iron, one is 90F and the other is 70F. Place them touching side by side. Immediately, the heat will flow from the hotter one until they are both equal in temperature. Even if you insulate between them, although it slows the process, the heat will flow from heat to less heat.

Law 3 – When a liquid changes to vapor, it gives up its heat in the form of vapor.

When water changes state and turns to vapor, the liquid is giving up it’s heat in the form of vapor. Try this, put two containers of water outside (in the summer), one with a cover and one without a cover. After several hours, measure the water temperature of both containers. The one without the cover will be 15-30F cooler because the water is evaporating (turning to vapor or changing state).  Changing the state of liquid to vapor takes a tremendous amount of heat energy, many times more than just raising the temperature of the water.

Any liquid capable of boiling or changing state can be used as a refrigerant.

If you can get clear and really understand these three laws, you are well on your way to becoming a top notch air conditioning technician.

Our HVAC Technician Certification Course goes into more detail on the laws of thermodynamics and refrigeration.

About The Author

Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.