Seeking SciNote, Chemistry: Air Conditioning
How does air conditioning work? I know temperature is related to the kinetic energy of particles, so if you have AC blowing in your face, then all the air particles should be colliding with your face particles, so shouldn’t it feel hot?
Asked by anonymous
Air conditioning works by taking advantage of the fact that a liquid must absorb heat from its surroundings in order to undergo a phase transition into its gaseous form. Sweating works in the same way: as you perspire, your sweat will evaporate, thereby “removing” heat and keeping you cool. Remember the second law of thermodynamics, which states that heat can only move to areas where it is cooler, not the other way around.
Air conditioners use liquid chemicals called refrigerants to carry out the refrigeration cycle. Refrigerants must have a boiling point that is somewhere around the temperature you wish to cool to, as well as a high heat of vaporization (that is, the amount of heat it takes to convert the liquid to a gas). In the past, CFCs (chlorofluorocarbons) were used extensively as refrigerants; however, due to their effects on ozone depletion, they are no longer used in favour of more eco-friendly coolants.
Air conditioners have a few main components: an evaporator, a condenser, and a compressor. The first part of the air conditioner, the evaporator, does exactly what it sounds like it does. As the refrigerant moves through the evaporator coils, a fan blows hot air across them, exciting the molecules and causing them to use this energy to transition to a gaseous form. It is this process that causes the temperature in the room to lower.
So that’s it, we’ve cooled the room. We must be done, right? Not quite. The heat is still in the system, and in order to keep cooling, the cycle must be completed by having the gaseous coolant transition back to its liquid state. After passing through the evaporator coils, the refrigerant enters the compressor. Here, the gas is subjected to high pressure, but it does not become a liquid just yet. As the gas passes through and is compressed, it actually becomes even hotter.
Finally, the super-heated gas enters the condenser. Just like the evaporator, the condenser is made up of a series of coils that also has a fan blowing air across them. As the air passes across the condenser, it removes the heat from the refrigerant. Because the refrigerant is still under great pressure but has had the heat removed from it, it becomes liquid once again and goes back through the system, completing the cycle over and over again.
Answered by Rachel Rockwell, Expert Leader.
Edited by Margaret Gordon, Editor.