An air conditioner is an electromechanical device that is used to regulate both the temperature and the humidity within a living space. These devices have found application in residential, commercial and industrial properties. The air conditioning unit has gained more significance as more and more people become aware of the apparent impact that air quality has on health. It has been shown that breathing fresh clean air has both indirect and direct benefits to the well-being of an individual. Air conditioners use a liquid that alternates between gas and liquid to bring about the cooling of air. This liquid is known as the refrigerant. The same core principles that work in the air conditioners are also used in the refrigeration units with only a few structural differences between the two. The use of the air conditioner did at one time come under serious controversy after scientists realized that the chlorofluorocarbons used as refrigerants were responsible for the depletion of the ozone layer. Since then, air conditioning unit and refrigerator manufacturers switched from using chlorofluorocarbons to ammonia, sulphur dioxide and gaseous alkanes.
The principles of air conditioning
An air conditioning unit is made up of four main components regardless of the configuration of the particular air conditioning unit or system. These four components are:
a. The Compressor unit
b. The Condenser coil
c. The Evaporator coil
d. The Expansion valve
In order to fully understand how an air conditioner works it is best to understand the underlying principles through which the air conditioner carries out its function. These principles are listed according to the order of their application in the air conditioning unit. The air conditioner uses only four principles in its operation. These principles are:
1. As a liquid turns to a gas it tends to absorb heat from the surroundings
Everyone is aware that before a given volume of water turns into water vapor, the water must be heated to its boiling point. The air conditioner makes use of this principle to cool the warm air that passes over the evaporator from a room or building. To start with, the refrigerant is in the form of a low-temperature high-pressure liquid just before entering the evaporator coils. This refrigerant first passes through the expansion valve prior to entering the evaporator coils. The expansion valve allows for the abrupt increase in the diameter of the pipe carrying the refrigerant. The increase in diameter allows the low-temperature high pressure liquid to instantly turn to gas. The refrigerant being a gas at room temperature needs to absorb heat energy from its surroundings in order for it to retain its gaseous state. The gas draws the heat from the evaporator coil cooling it to sub-zero temperatures. Therefore as warm air from a room or house passes over the super cool coils, a similar cooling effect occurs. The end result is that the air that has gone past the evaporator coil acquires a far lower temperature than the air yet to reach the coils.
2. The compression of a gas causes its temperature to rise
It is common knowledge that when a gas is heated it tends to expand. This can be demonstrated by heating water in a container with a small opening. High pressure steam emerges once the boiling water turns to high pressure gaseous water vapor. In a similar manner cooling a gas causes it to contract. This is shown by the instantaneous implosion of an air tight container containing boiling water when it is abruptly cooled. Following this line of logic it is clear that increasing the pressure of a gas by mechanically compressing, it should in effect cause its temperature to rise. An air conditioning unit makes use of this principle in its compressor. The low-pressure low-temperature refrigerant gas coming from the evaporator coils is turned into a high-temperature high-pressure gas. The action through which the compressor draws the low-pressure low-temperature from the evaporator facilitates the flow of the cooling gas through the evaporator coils.
3. Cooling a gas turns it into a liquid
This principle is demonstrated by condensation whereby water vapor turns into a gas after cooling on a cold surface. In the air conditioner this same principle is demonstrated in the condenser coils. The high-pressure high-temperature gas from the compressor then flows to the condenser where it heat up the coils. Cool air is drawn in from the outside air and is forced to pass through the condenser coils. As the cool air passes across the condenser coils it draws out heat from the coils and thereby drawing heat from the hot refrigerant inside. This in turn converts the high-pressure high-temperature gas into a high-pressure low-temperature liquid. This form of the refrigerant is what flows into to the expansion valve just before entering the evaporator coils. At this point the refrigerant has made a complete circuit through all the components of the air conditioning unit.
4. The ability of air to hold water in the form of humidity depends on its temperature
This last principle works outside the air conditioning unit and is responsible for the regulation of the humidity of the circulating air. This principle can be illustrated by the oppressive heat that precedes an oncoming storm. Due to the higher moisture content of the air, the air is able to hold a lot more heat. The opposite application of the same principle can be demonstrated in the freezing nights in desert areas. The low humidity of desert air lowers the ability of the air to retain heat when it is no longer available from the sun.
This principle is demonstrated at around the evaporator coils. As warm air is force over the evaporator coils, the air is cooled. This also causes some of the water vapor contained in the air to freeze over the evaporator coils as frost. The lower temperature of the air that has already passed over the operator coils, lower the ability of the air to hold water in the form of water vapor. This implies that the air from an air conditioner unit is cool and dry. Having broken down the working of the air conditioner into these four principles it is far easier to understand the working of the air conditioner.