An air conditioning unit cools the air in a room through a process called refrigeration, which involves several key components and a refrigerant fluid. Here's a basic overview of how an air conditioner works to cool the air:
Refrigerant: The air conditioning unit uses a chemical compound known as a refrigerant, which has properties that allow it to change from a gas to a liquid and back again at low temperatures. Commonly used refrigerants in the past, like CFCs (chlorofluorocarbons), have been phased out due to their harmful impact on the ozone layer. Modern air conditioners use more environmentally friendly refrigerants like HFCs (hydrofluorocarbons) or HFOs (hydrofluoroolefins).
Evaporation and Compression: The refrigeration cycle starts with the refrigerant in a gaseous state. The compressor in the AC unit pressurizes the gas, causing it to become hot. This high-pressure, high-temperature gas then flows through the condenser coils, where it releases heat to the outside environment, making the refrigerant condense into a high-pressure liquid.
Expansion Valve: After being condensed, the high-pressure liquid refrigerant passes through an expansion valve (also called a throttle valve). This valve reduces the pressure on the refrigerant, causing it to rapidly expand. As it expands, the refrigerant turns into a low-pressure, low-temperature mixture of liquid and gas.
Evaporator Coils: The low-pressure, low-temperature refrigerant mixture now enters the evaporator coils located inside the indoor unit of the air conditioner. The warm air from the room is blown over these cold coils by a fan.
Heat Exchange: As the warm air passes over the cold evaporator coils, heat from the room air is absorbed by the refrigerant, causing it to evaporate back into a gas. This process extracts heat from the indoor air, cooling it down.
Cool Air Delivery: The now-cooled air is then blown back into the room, while the heated refrigerant gas is carried back to the compressor to start the cycle again.
This continuous cycle of compression, condensation, expansion, and evaporation allows the air conditioning unit to remove heat from the indoor air, thus cooling the room and making it more comfortable.
It's worth noting that some air conditioners also have a "reversing valve" that allows them to function in reverse, providing both cooling and heating capabilities. When in heating mode, the AC unit extracts heat from the outside air and transfers it indoors, effectively heating the room. This process is commonly known as a heat pump.