AC Demystified

How Does Air Conditioning work?

It has been said that when we clean, we are actually just moving the dirt around. It is true when you think about it; We are merely removing the dirt and dust from places where we don’t want it and taking it to somewhere more desirable. Well, the exact same thing can be said about Air Conditioners. Just as with matter, we cannot create or destroy energy. We are merely taking the energy (heat) from somewhere we don’t want it (inside our home) and dumping it somewhere more desirable (outside).

We accomplish this by creating a loop that runs from inside our homes to the outside and back again. We fill this loop with a refrigerant which has a set of specific chemical properties to make it easy to manipulate. This refrigerant serves as the vehicle for taking the heat and delivering it outside. This begs the question: How do we add and remove heat from this substance?

Let’s answer that question by further examining our loop. Along the course of this loop there are 4 key stations, 2 of which change the state of the refrigerant and 2 of which change the pressure:

1. Somewhere inside your home, typically integrated with a furnace, there is what is called an evaporator coil along with a fan. Inside the evaporator coil is the refrigerant, cold and in liquid form. The warm inside air is blown over this coil by the fan, cooled and then distributed to the house. The heat from the home is absorbed into the refrigerant which causes it to evaporate into gaseous form.
2. As this gas is heading outside it is highly pressurized by a compressor, which causes it to heat up even further. Now it is even hotter than the outside temperature, even on the hottest summer day.
3. Outside, the hot gas enters what is known as the condensor coil. Once again we have a fan blow air over it and transfer heat from the refrigerant into the outside air. As you may have guessed, this causes the refrigerant to condense back into liquid form. This coil, along with the compressor, typically sit together outside in a metal enclosure. This enclosure is the device we typically picture when we think of AC.
4. Finally this liquid returns into the house and is decompressed by running through an expansion device, which can come in various forms. Reducing the pressure of the liquid causes it to cool drastically. Now we can use it to absorb some more heat from the home, and the cycle continues!

Incidentally, this is exactly how your refigerator works as well, only on a smaller scale. The same concept is used to keep both you and your tomatoes from turning into hot mush.

What about Heat Pumps?

Somewhere along the line someone had the bright idea that if we can take heat from inside and dump it outside in the summer, why don’t we grab heat from outside and dump it inside in the winter? Well that is exactly what a heat pump is, an AC system in reverse! It has several relatively small modifications to make it run effectively in this way, but uses virtually all the same components.

This also serves as a fun example of how bad tradesmen and contractors are at naming things, as technically both of these systems pump heat and condition the air, but that’s a story for another day!