Episode 3 - Air Conditioners

Air Conditioners–

Hello, and welcome to episode three of the How Things Work podcast. My name is Jamie Aycock, and in each episode we’ll explore the inner workings of things we see and use every day. As it’s about 99 Fahrenheit (37 Celsius) outside, in this episode we’ll explore how air conditioners work.

Most air conditioners (and refrigerators and freezers) have four main components – condenser coils, evaporator coils, a compressor, and an expansion valve. Flowing through this series of tubes, compressors, and valves is a refrigerant like Freon. The basic law of physics behind the operation of air conditioners is called the ideal gas law. The ideal gas law states that the pressure of a gas multiplied by its volume is equal to the temperature times a constant times the amount of the gas. For our discussion, we can simplify that a bit and say that as we pressure a gas, the temperature will increase. Likewise, as we de-pressurize a gas the temperature will decrease. Take a look at the Wikipedia entry for more detail on the ideal gas law if you’re interested.

To give a basic description of how the parts of an air conditioner are arranged in a typical system, the compressor sits outside the building along with the condenser coils. The condenser coils are connected to an expansion valve, which is then connected to the evaporator coils, which are located within the building to be cooled. The evaporator coils connect back to the compressor, completing the loop.

The refrigerant is compressed by the compressor (big surprise there!). Remembering what we said about the ideal gas law, once the gas is compressed we know that it has heated up. This heat has to be dissipated, so the now hot refrigerant flows through the condenser coils. Usually a big fan blows across these coils outside, venting as much of the heat as possible. The now cooler (but still warm) refrigerant flows through the expansion valve, dropping in pressure as it does. As the pressure of the refrigerant drops, the temperature drops as well. The now very cold refrigerant flows through the evaporator coils. Here’s where the big payoff occurs. The refrigerant cools the evaporator coils and air is blown across these coils inside the house or building to cool the building. This cool air is routed throughout the house by the ductwork, spreading relief to everyone.

One way to look at the air conditioner system is as a machine that simply moves heat from one place to another. When we’re trying to cool things off inside, we’re taking heat from the inside of the building and dumping it outside. When we look at the air conditioning system like that, an easy question to ask would be “can we do the opposite to heat the inside of the house?� Absolutely! If your home has a heat pump installed to provide warmth during the cold months, that’s exactly what is happening. When the temperatures dip and you move the switch on your thermostat from “COOL� to “HEAT�, the air conditioner basically runs backwards. The compressed refrigerant flows through the coils inside the building, venting its warmth. The refrigerant then flows through the expansion valve, cooling it off. After cooling off, the refrigerant travels through the coils outside the house (the coils that used to be the condenser coils, now acting as the evaporator coils), warming the refrigerant up a bit (even in the cold of the winter).

That’ll wrap things up for this episode of How Things Work. A transcript of this episode can be downloaded from howthingswork.libsyn.com, and if you have any questions, comments, or topic ideas, please drop me a line at [e-mail]. Thanks for listening.

The music you heard was How’d You Know That by Scott Brown. It’s available on Random Chance records at www.randomchancerecords.com and is made available through the IODA Promonet.

 

Citations –

http://home.howstuffworks.com/ac1.htm

http://en.wikipedia.org/wiki/Ideal_gas_law