In order to stay cool and comfortable, we rely on our air conditioning systems. But, how exactly do they work?
In the spirit of going back to school, here’s a refresher course on the basic workings of an air conditioner.
How does air conditioning work?
Most air conditioning systems are “split systems,” meaning there is an inside unit—comprised of a blower, air filter, and cooling coils—and an outside unit—comprised of a compressor, fan, and condenser coils.
If you have a furnace, the cooling coils, known as evaporator coils, sit on top of the blower. The indoor evaporator coils are connected to the outdoor condenser coils in a closed loop. The coils contain a chemical known as refrigerant.
When your thermostat hits a set temperature, it sends out two signals, one to the unit outside to turn on the compressor, which is like a pump that starts circulating the refrigerant. The fan also turns on outside. The second signal tells the indoor blower to turn on. Then, the return vents start sucking in the warm and humid air in the house and back to the indoor air handler, where it then flows past the evaporator coil. The evaporator coil, since it’s extremely cold, absorbs the heat from the air and sends the heat outside to the condenser coils. The fan helps dissipate the heat from the coils until they are cool enough to start the process all over again.
Things get a bit more complicated because we have to change the pressure of the refrigerant to gain or lose heat, but these are the basics.
The same refrigeration cycle is how your refrigerator works. Refrigerant absorbs heat from the inside of the fridge and displaces it on the outside, usually via coils on the back of the fridge.
Main Parts of an Air Conditioner
Your air conditioning system is comprised of five main parts:
If you’ve ever walked past an outdoor condensing unit, it’s hot! That’s because the air conditioner is releasing heat gathered from inside the home to the outdoors. An air conditioner moves heat using refrigerant, also known as coolant or the brand name Freon ™.
Refrigerant can change temperature through different principles of physics, known collectively as the “combined gas law.”
Basically, the combined gas law joins three separate gas laws: Boyle's Law, Charles' Law, and Gay-Lussac's Law.
The equation looks like this: PV / T = k
P = pressure of the gas
V = volume of the gas
T = absolute temperature of the gas
k = a constant (for a fixed amount of gas)
This equation tells us that when the pressure of a gas increases, so does its temperature. The opposite is also true: when you decrease the pressure of a gas, the temperature decreases as well.
In an air conditioner, a compressor increases refrigerant pressure and a metering device lowers refrigerant pressure. This raises or lowers the temperature of the refrigerant.
The compressor is located in your outdoor air conditioning unit (also known as a heat pump), usually located on the side or roof of a building. As the name implies, the compressor literally compresses vapor refrigerant, creating higher pressure and with it, higher temperature. It does this by decreasing the volume of the space that the refrigerant is in to increase its pressure.
This hot gas is then transferred to the condenser. Once inside the condenser coils, it loses its heat to the outdoor air with the help of a high-powered fan.
You may be wondering why we have to increase the temperature of the refrigerant. In order for heat to transfer to the outdoors, it must be hotter than the outdoor environment. Considering we use air conditioners when it’s hot out, the refrigerant has to be even hotter.
The second law of thermodynamics asserts that heat always flows naturally from hotter to colder bodies, and not the reverse. For heat to flow out of the refrigerant, it must be hotter than the outdoor temperature. When the refrigerant leaves your evaporator coils, it is still not warm enough, which is why we need to increase the pressure and temperature first.
After the compressor has increased the temperature of the refrigerant, it’s now ready to enter the condenser coils. As the condenser fan blows air over the coils, heat gets transferred to the outdoor air. This is the heat that used to be in your home. The high-pressure, hot vapor refrigerant cools down until it condenses and becomes a liquid.
4. Metering Device (aka Expansion Valve)
When the liquid refrigerant leaves the condenser, it is still too hot. The metering device has two jobs: it controls the flow of refrigerant into the evaporator and lowers the pressure of the refrigerant until it reaches saturation pressure-temperature.
The indoor air handler contains evaporator coils as well as a fan that blows air over the coils. When the air inside your home blows over the evaporator coils, it absorbs heat energy because the coils are so cold. Remember, heat naturally flows from hot to cold.
When enough heat gets absorbed by the evaporator coils, the refrigerant inside turns from liquid to a vapor. The refrigerant goes from being a cold liquid to a hot vapor and then gets passed on to the compressor where the heat is removed from the home.
If you have any questions about how your air conditioner works, contact Sobieski Services. We’re here to educate you on all things HVAC all year long.
At Sobieski Services, our goal is to help our customers in Delaware, Pennsylvania, Maryland, and New Jersey learn more about energy and home comfort issues — especially HVAC and plumbing issues — so that they can save money and live in healthier, more comfortable homes.