What Actually IS an Air Conditioning Unit?

ac unit trane

You rely on it to keep you cool all summer long, but do you know how your air conditioning actually cools the air? That unassuming metal box sitting in your yard is a lot more complex than you might think. The scientific concept that it relies on for its cooling action is surprisingly simple. Find out how air conditioning units really work to get a deeper appreciation for this otherwise humble household appliance.

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An Accidental Invention

Willis Carrier

The inventor of modern air conditioning, Willis Carrier

Air conditioning was created purposely by Willis Carrier, but it was originally intended to lower the humidity of a room or space. Carrier worked at a printing company that was having trouble applying inks to a paper that absorbed too much moisture in the humid summers. He experimented until he created a system that involved blowing air over a series of cold metal pipes. This took advantage of the refrigeration cycle, a natural phenomenon that causes moisture in the air to condense into liquid water when it cools enough. While the invention certainly worked to combat humidity in the printing rooms, Carrier also noticed that it left the air cooler as well. This isn’t because the pipes are adding any “coolness” to the air, but rather that heat is transferring into the chilled pipes and therefore out of the air. The result is cooler and drier air, and reducing humidity also makes the air feel cooler than the actual temperature.

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Your Air Conditioner

The AC unit cooling your home follows the same basic principles of that first air conditioning system. Instead of chilled pipes, a coiled metal pipe known as an evaporator is tucked inside the outdoor unit. This provides the cooling effect thanks to pressurized refrigerants that change phase from gas to liquid readily at normal outdoor temperatures. This allows the A/C unit to create a chilling effect as necessary because the refrigerants require heat to convert back and forth from gas to liquid. Any air blown over the evaporator is cooled, and humidity gathers on the cold evaporator to further cool the air through the reduction of humidity as well. A condenser coil carries the heat away so it can be exhausted out of the A/C, which is why you’ll often feel blasts of hot air coming out of the vents in the summer.

how ac unit works

An air conditioning systems diagram

An expansion valve is responsible for regulating the amount of refrigerant in the system, so it’s essential for getting the right amount of cooling. This means that a broken valve can lead to a lack of cooling altogether, or it can cause your system to freeze up when too much refrigerant is constantly flowing through the evaporator coil. The system also stops working if any of the many blower fans inside the A/C system stop working. Most air conditioners include at least one fan each for both the evaporator and condenser coils, along with a master blower inside the house that moves the air through the ducts and around the hours. Zoned cooling systems may have half a dozen or more extra fans to keep air moving and divide it into the various zones around the house.

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