Thermal energy is all around you, which makes it a very important concept for any heating and cooling specialist to understand completely. What started out as simple experiments with liquids led to an excellent understanding of the concepts of thermal energy, heat, work, and everything that makes a current day heating and cooling system function properly.

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Who Discovered It

Thermal energy is represented in Joule units today because of James Prescott Joule, the man who discovered that heat is actually an energy type.  He was an English physicist, studying relationships between temperature, heat, and work when he made the discovery. During his testing he realized that simply agitating the water mechanically would raise its temperature.

How the Joule is Used Today

Today the joule is used for a variety of calculations that include thermal energy, heat, and work. A single joule is the measurement that represents one newton moving an object one meter. To bring you back to a more familiar concept that’s a bit less scientific, 1,000 joules make up one British thermal unit or Btu, a concept most people who’ve ever purchased a furnace are quite familiar with. Each time that you shop around for the best furnace, or an HVAC professional calculates what type of system you need for your home, you are going off the work done by James Prescott Joule.

What is Thermal Energy?

Thermal energy is actually a type of kinetic energy possessed by different objects. Heat in an object is actually just faster moving molecules. When you heat up a frying pan to cook your eggs in the morning, you’re speeding up the pan’s molecules to make it hot enough to actually cook the egg. The same can be said for just about anything else that gets hot as well. Many heaters work by warming up air, which is making its molecules move faster.

The Difference Between Heat and Thermal Energy

While thermal energy is the speed an object’s molecules are moving at, heat is actually the transfer of this energy from one object to another. When your stove applies heat to a pan of oil, the thermal energy is being transferred from the stove element to the pan and from the pan to the oil within. Some of the heat is transferred to the air around the stove as well, which is why kitchens seem to warm up so much when you get to cooking.

How Heat Works

If you’ve ever witnessed a mosh pit in progress, you should be able to understand how heat works quite easily. Take, for instance, the stove and pot example once again. The stove element is heated up through the burning of gas and creation of a flame, or through electricity moving through a resistor rapidly. When the element heats up, its molecules start moving back and forth rapidly. They keep bumping into one another and speeding up more and more until you set a pot down on top of the element. Now those molecules start bumping into the pan’s molecules and they start moving faster as a result. The motion from the element molecules continually transfers to the pan’s molecules and the pan’s molecules begin crashing into molecules farther up the pan and against molecules within the pan as well. This is known as conductance and it’s how thermal energy is typically transferred around a home, or most other places for that matter.

Understanding Work and Heat

Although work and heat are related, they’re far from the same thing. They both represent the transfer of energy from one place to another, but heat is this transfer through thermal interaction or molecules colliding into one another and speeding each other up. Work, on the other hand, is the transference of energy through any other means.

The most important thing to know about work and heat is that work can be completely converted into heat, but heat can only be partially converted into work. Think about a steam engine and how it relies on fire to create motion. That’s an example of heat being transferred into work, but as you know steam engines are notoriously inefficient. The internal combustion engine is another example of this—though it’s more efficient, it still uses much more heat energy than it generates work to move the vehicle along.

To flip the idea around, a heat pump is an excellent example of work being used to trigger heat. A compressor condenses a refrigerant and a series of expansion chambers allow it to expand strategically. These two mechanics facilitate the transfer of heat from one location to another, which is essentially heat, but done through the mechanical work of the compressor.

When you understand the concept of thermal energy, work, and heat, it makes it much easier to understand how advanced heating systems work, as well, and how engineers can figure out which materials are the best to use for furnaces, ducts, and other important heating components.