How the Quirky A/C cools a room

GE Aros Smart Window A/C

With temperatures on the way up throughout the country A/C purchases are on the rise. Homeowners like having cooler rooms and homes, though over time the A/C unit has become something like the family car in that we don't know how they work. So, how do they work?

Let's start at the beginning. The simple idea that makes an air conditioner work is that heat is transported from one place (the room or the house) to another place (outside). To make this happen, five components work together to move the heat:
  • Compressor
  • Refrigerant
  • Condenser
  • Expansion Valve
  • Evaporator Coil
As you know, since you are reading this blog, there are many types of A/Cs including whole-house models, window models, and the ductless A/C which is finally gaining popularity in the USA. All of these systems use the five components listed above. Let's spend just a minute on each of them.

The compressor is the core component in the system, much like your heart. Compressors are pumps that move refrigerant throughout the system.

Refrigerant is an element that transports heat away from your living space. When it is cool, it is a liquid and when it is hot, it is a gas. This state change coupled with the compressor is what really allows an A/C unit to work.

This is where refrigerant in vapor form (when it is hot) goes to cool down. There is typically a fan that blows outside air over metal fins or pipes to remove some of the heat from the refrigerant. At the condenser, the refrigerant transitions from vapor to liquid, but it is still hot. If you have a whole-house A/C unit, this is the thing sitting outside with the big fan in it. In a window A/C unit, this is located on the exterior side of the unit.

Expansion Valve
The expansion valve is where the somewhat cooler refrigerant goes from high pressure liquid on the intake side to a low pressure gas on the output side. Thinking back to chemistry, you learned that a gas cools as it expands, and that is exactly the process at work here. The result is low pressure liquid that is cool.

Evaporator Coil
The low pressure refrigerant comes to the evaporator coil next. This is where the refrigerant meets the warm air in your house and picks up the heat from the air. The result for the air is that it is cooler since it transferred heat into the refrigerant. The result for the refrigerant is that it is hot again, so hot that it changes to vapor and now that it is a vapor, it moves on through the compressor and the processes is repeated.

There you have it. Now you know almost all there is to know about how an A/C unit works. Of course there are some physics involved if you want to know more visit The Physics Hypertextbook where there is a page dedicated to refrigeration physics.