Air conditioning works by removing heat from a room using a refrigerant that changes from gas to liquid. The compressor compresses the refrigerant, making it very hot, and it passes through condensing coils outside the room, dissipating heat. The refrigerant then goes through an expansion valve, evaporates, and removes heat from the surrounding air. The process repeats until the thermostat registers a specific temperature. Energy-saving measures can help air conditioning systems work more efficiently.
Contrary to popular perception, air conditioning (AC) isn’t about adding cool air to the room, but rather taking the heat away. The end result is a space with far less heat, making it feel cooler for the occupants. Air conditioning harnesses the effects of evaporation, just as an alcohol swab makes a person’s skin feel cooler as the liquid evaporates. Alcohol does not lower a person’s skin temperature, but rather draws heat from the air as it turns into a gas.
Air conditioning units contain a special chemical called a refrigerant, which has the unique ability to change from a gas to a liquid in a short amount of time. A refrigerant called freon is commonly used in AC units, although other commercial refrigerants are available. Refrigerant is pumped into the unit at the factory, along with a small amount of lubricating oil for the compressor.
The parts of a typical AC unit usually form a closed system consisting of a compressor, condenser, expansion valve, and thermostat. Motorized fans help circulate conditioned air, while thin metal fins allow for rapid heat dissipation. The heaviest part of a typical air conditioner is often the compressor, as it needs to be strong enough to handle a significant amount of pressure.
The process of cooling an area begins with the refrigerant entering the compressor, usually located at the bottom of the unit. At this point, the refrigerant is a cold gas. When the gas enters the inner chamber of the compressor, the compressor compresses the refrigerant and the gas becomes a very hot gas under high pressure. This hot gas passes through a series of condensing coils placed outside the room to be cooled. The heat dissipates into the outside air, much like a car radiator dissipates heat from the engine’s coolant. Once the refrigerant reaches the end of these coils, it is significantly colder and in liquid form.
This liquid is still under high pressure, like the contents of an aerosol can. In the case of air conditioning, liquid refrigerant is forced through a very small opening called an expansion valve. Liquid coolant comes out the other end of the expansion a very small amount at a time. As the refrigerant evaporates at a much lower temperature than water, it begins to evaporate as it travels through another set of coils. It is this evaporative action that removes heat from the surrounding air, including the air contained in the room. The unit’s fan blows through metal fins placed on these coils, causing a cooling sensation in the room.
At this point, the liquid refrigerant has reverted to a cold gas and re-enters the compressor, where the whole process begins again until a thermostat registers a specific temperature and shuts down the compressor. As the room warms up, the thermostat senses the added heat and the compressor turns back on to create more pressurized hot gas. At some point, the room temperature may equal the cooling power of the air conditioner and the compressor will shut down again. The air conditioning systems in most homes benefit from energy-saving measures such as using awnings and closing the doors, since they don’t have to work as hard to keep the room at an acceptable level of cooling.
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