It Doesn’t Produce Cold. It Moves Heat.
This is one of those facts that can surprise even people who use air conditioning every day. Contrary to popular belief, an air conditioner is not a device that produces cold.
– From the point of view of physics, we do not speak about producing cold. Instead, we remove thermal energy from one place and transfer it to another. An air conditioner is simply a highly efficient heat pump that transports heat – explains Prof. dr hab. Paweł Kowalczyk, Head of the Department of Solid State Physics at the Faculty of Physics and Applied Informatics.
The easiest comparison is a refrigerator. Its interior remains cool not because the appliance creates cold, but because it removes heat from the food stored inside and releases it into the kitchen through the heat exchanger located at the back of the unit.
An air conditioner works in exactly the same way. However, instead of cooling a few shelves of food, it removes heat from an entire room and transfers it outside the building.
Everything Begins with Evaporation
How can the operating principle of an air conditioner be explained without looking inside the device?
It is enough to think of a cup of hot tea left on a table. Over time it cools down because some of the water evaporates from its surface. The molecules leaving the liquid carry away thermal energy, making the drink progressively cooler.
The human body uses the same mechanism. When sweat evaporates, it removes heat from the skin and helps maintain the proper body temperature.
An air conditioner relies on exactly the same phenomenon. Instead of water, however, it uses a special refrigerant that changes very easily between liquid and gaseous states.
The Invisible Hero of the System
The refrigerant circulates within a tightly sealed system.
Inside the indoor unit, it begins to evaporate. To change its state, it absorbs energy from the air flowing through the heat exchanger.
This is why the air leaving the unit becomes cooler – part of its energy has been absorbed by the refrigerant.
The gas is then directed to a compressor, where it is compressed significantly. As the pressure increases, so does its temperature.
– The compressor performs the greatest amount of work in the system. It makes the refrigerant hot enough to release the heat it has previously collected into the air outside the building. Energy does not disappear – it simply changes location – emphasises Prof. Paweł Kowalczyk.
Where Does the Heat Go?
Many air-conditioning users ask this question.
The answer is simple – nowhere.
If we stand next to an operating outdoor unit, we can feel warm air being expelled. This is the very same energy that, only moments earlier, was present in our room.
After releasing its heat, the refrigerant changes back into a liquid and returns to the indoor unit. There, the entire process starts again and repeats itself hundreds of times every hour.
Why Does an Air Conditioner Need Electricity?
If the device does not produce cold, what is electrical energy needed for?
Primarily to power the compressor and the fans. These components make it possible to transport heat from inside the building to the outside.
It could be said that an air conditioner is a heat pump operating “in reverse” – instead of heating a room, it removes thermal energy from it.
How Does an Air Conditioner Work in Four Steps?
① Evaporation
The refrigerant evaporates in the indoor unit, absorbing heat from the air in the room.
② Compression
The compressor increases the refrigerant’s pressure and, consequently, its temperature.
③ Heat Release
In the outdoor unit, the hot refrigerant transfers its energy to the outside air and condenses back into a liquid.
④ Return
The cooled refrigerant returns to the indoor unit, where the entire cycle begins again.
The Physics That Keeps Us Cool in Summer
Air conditioning is one of the best examples of how the laws of physics translate into everyday comfort. Phenomena associated with evaporation, pressure changes and the transfer of thermal energy make it possible to cool homes, schools, laboratories and lecture rooms effectively.
The next time you breathe a sigh of relief after stepping into a cool room, remember that the air conditioner has not created cold. It has simply used the laws of thermodynamics to move heat somewhere it bothers us less.
Source: Prof. dr hab. Paweł Kowalczyk
