The Refrigeration Cycle - How an Air Conditioner Works

How an Air Conditioner Works

The above diagram depicts a simple air conditioner. Inside an air conditioning system is a chemical refrigerant which is a compound that easily changes states from liquid to vapor and back again. In addition to refrigerant, an air conditioning system requires a minimum of four components, the compressor, condenser, metering device, and evaporator.

Component #1: The Compressor

The compressor is the heart of the system. Just like your heart pumps blood through your body at a specific flow rate and pressure, the compressor pumps the refrigerant through the air conditioning system at a designed flow rate and pressure.

When the refrigerant enters the compressor it is in a vapor state. It enters the compressor because it is literally being sucked into it. That is why the side of the compressor where refrigerant enters is called the suction side or low pressure side. As the name suggests, the compressor compresses the vapor as it is being pumped through it. When a vapor is compressed both the pressure and temperature of that vapor increases. The vapor leaving the compressor is very hot. You will get burnt if you were to touch the copper refrigerant lines coming off of the compressor. In the above diagram the high pressure vapor refrigerant is represented by red dots.

Component #2: The Condenser

The high temperature refrigerant passes into a condenser coil. As the vapor refrigerant travels through the coil, air from a fan passes over the coil to cool the vapor refrigerant. As the vapor cools it condenses and becomes a liquid, which is referred to as a change of state. This change of state from vapor to liquid is essential. You may be somewhat familiar with a typical home system where the condensing unit sits outside. When operating you can place your hand over this unit and feel the warm air being blown out. High temperature vapor refrigerant enters the unit as the heat energy in the vapor is removed by blowing air across the condenser coil. While this is happening, the vapor changes to a liquid. The heat being blown from the condensing unit is the heat that used to be in your home. In the above diagram the liquid is represented by solid red.

Component #3: The Metering Device

The metering device controls the flow of the liquid refrigerant to the next component which is the evaporator. This is a dividing point between the high pressure and low pressure sides of the system. As this high pressure liquid is passing through the metering device and into the evaporator the pressure drops.

Component #4: The Evaporator

After leaving the metering device the refrigerant immediately enters a coil called the evaporator. This coil or evaporator has a fan blowing across it. As the refrigerant enters the coil at a lower pressure it begins to boil and change state back to a vapor. During this process of changing state, energy in the form of heat is being removed from the air passing over the coil and is being absorbed by the refrigerant. The heat that was in the air is transferred into the refrigerant. Since heat was removed from the air blowing over the evaporator coil, the air leaving the evaporator coil is cold. In short, air conditioners make cold air by using a refrigerant to absorb the heat in the air.

Now that heat from your computer room, office area etc. is in the refrigerant what do we do with it? The heated refrigerant vapor is sucked into the compressor and pumped back to the condenser coil. Here, in the condenser, the heat that was earlier absorbed by the refrigerant in the evaporator section from the space we are cooling is released and removed. The process of the refrigerant “changing states” from vapor to liquid (releasing heat through the condenser) and from liquid to vapor (absorbing heat in the evaporator) is the central mechanism of air conditioner cooling.

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