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A typical central air conditioning system utilizes a split configuration and has one part outside along with an indoor section that moves the air through the structure through metal or fiberglass ducts. The cooling effect is attained with the use of a refrigerant (FREON) Freon is actually a brand name that most people associate with the gas that is used in air conditioning systems. Some other brand names you may not be aware of are Forane and Puron. The cooling effect that we all enjoy is the result of the rapid expansion of this liquefied gas. Water for example can be in some cases considered a refrigerant. When water is vaporized (boiled) the temperature of the material it is in contact with will drop as a result. However water has corrosive properties that make it undesirable for use in air conditioning systems. That is why we use chemicals like Freon.
The refrigeration cycle may be described as follows. Cool low pressure refrigerant vapor enters the compressor where it is compressed to a high pressure high temperature state still in a gaseous form. From there it is sent through pipes to a coil where the heat is removed with the use of a fan. The removal of heat from the gas causes it to condense into a high pressure medium temperature liquid. From this point in the cycle it is transported through pipes to another coil where the cooling effect is desired and passes through a device that meters its flow and reduces the pressure. This reduction in pressure causes the liquid refrigerant to evaporate or boil off rapidly and absorb heat in the process. When this vaporization is complete the refrigerant is again in a low pressure gaseous state and the process starts over again.
The difference between an air conditioner and a heat pump is simply a 4-way valve that reverses the flow of the refrigerant changing the cooling coil into the heating coil where heat from outside is moved inside. Yes even when it feels cold to us outside heat is still present in the air. That is why when you feel the air coming out of the outdoor fan in the winter time it is colder than the surrounding air. The heat has been removed. There are a few more components involved in a heat pump to help it work continuously that we won’t discuss here but that is the basics of how a heat pump and an air conditioner works.
I was asked once to describe how this cooling effect is accomplished through the use of Freon and this is how I replied.
Imagine a one foot square in front of you and in this space is a gas and for simplicity let’s use the air you are breathing. This one cubic foot of air is at the same temperature of the area around you but the cube is sealed so no air can escape. This air inside the cube contains a specific amount of heat energy. Now imagine taking this cube and squeezing it down through whatever means, your own strength or some kind of machine to one half of a cubic foot. Now this one half cubic foot of air will be under a higher pressure as well as a higher temperature because you have taken a specific amount of heat in a specific area and concentrated it into a smaller space. It is still the same amount of heat but in a smaller space. Now if we allow the air to cool and expand the one half cubic foot back to one cubic foot the reverse will happen. Then all you have to do is replace the air with a different gas that will liquefy at a lower pressure and yes air will liquefy but at a very high pressure that would be dangerous to work with. When a gas changes state into a liquid (condenses) a specific amount of heat must be removed for this transformation to take place. This amount of heat is called hidden heat or latent heat and cannot be measured by a thermometer. We take advantage of this phenomenon in the refrigeration cycle which allows us to transfer a greater amount of heat with a small amount of refrigerant.
How does a a central air conditioning / heat pump system work?