Operation of air conditioner

We sweat when the weather gets warm. As sweats cool down, our temperature drops. This is because sweats take the heat away from our skin as they evaporate. When liquid evaporates and take heat away from the surroundings, it is called Latent Heat Of Vaporization. The bigger the Latent Heat Of Vaporization, the more heat it takes away. An air conditioner uses refrigerant with large evaporative latent heat. Let’s assume a refrigerant in a hot room. The refrigerant will take away heat from its surroundings to evaporate. If we enlarge the area of contact of the refrigerant to the air, the refrigerant will take away more heat. When we blow wind from behind the refrigerant, air that lost heat becomes cooler and the a cool breeze comes out from the front. The refrigerant used in an air conditioner tends to evaporate easily and have high Latent Heat Of Vaporization which make it perfect for a cooling device. Now, to understand how an air conditioner works, let’s follow the flow of a refrigerant. First, let’s look at the general flow. This is a compressor. If we compare a refrigerant to blood, a compressor is like the heart. A compressor circulates a refrigerant and compress it with high temperature and pressure. Then, the refrigerant pressed by the compressor flows to a condenser. While evaporation is the transition of liquid to gas through heat absorption, condensation is the transition of gas to liquid when it loses heat. A condenser serves to turn refrigerant in hot gas state into liquid form by taking away its heat. The refrigerant passed through a condenser becomes liquid and flows into expansion valve. There is a section in the expansion valve where the piping gets narrow and as the refrigerant passes here, it splits up into many pieces. What we see here is similar to the principle behind water being spread from spray. As the pressure on the refrigerant drops, its temperature drops dramatically as well. The refrigerant with lowered temperature then, goes into an evaporator to steal away heat. An evaporator is literally, a device that evaporates liquid into gas. Cooled refrigerant steals away the heat in the room and evaporates. The compressor and condenser are built inside the outdoor unit of an air conditioner. The evaporator and expansion valve are built within the indoor unit of an air conditioner, which is what we normally refer to when we talk about air conditioner. Now, let’s dive deeper into the functions of each mechanical components of an air conditioner. In the evaporator, refrigerant loses heat and is evaporated as gas into the compressor. When a piston compresses the gas refrigerant, its pressure rises and so does its temperature. We use products of spray type sometimes. You might have come across insect repellent spray or butane fuel canister whose surface of the can gets cooler after use. This is because the pressure inside the product has become lower. If pressure is lowered, temperature is lowered and if pressure goes up, temperature also rises. Now, coming back to the case of an air conditioner, when gas with low pressure and temperature is pressed by piston, its pressure rises and so does its temperature. However, more air conditioners nowadays use scroll type of compressor rather than piston type. In a scroll compressor, there are 2 scrolls of which one is fixed and the other rolls constantly. As more air coming through the entrance gets inside the scroll, space becomes crowded. As there is less space now, gas becomes more compressed and is discharged from the middle of the scroll in a compressed state. The reason for using such type of a compressor is the efficiency of space utilization. This type of a compressor allows the machinery to become smaller in size and reduces noise as well as vibration. Compressed air is then sent to a condenser to be pressed into liquid. The temperature of refrigerant passed through the compressor is above 80 Celsius which is in a hot gas state. This refrigerant passes through a condenser and is cooled down slowly with chilled air from fans. When liquid evaporates, it absorbs heat and becomes gas. As it transforms into gas, its kinetic energy becomes stronger. When the gas loses heat, its kinetic energy becomes weaker and it becomes liquid. In other words, chilled gas becomes liquid. A refrigerant in gas state of high temperature loses heat as it passes through a condenser. As such, it becomes condensed and at the exit, it turns into liquid almost. Although the refrigerant has thrown off some of the heat as it passes through a condenser, it is still hot, with temperature at about 50 Celsius. The refrigerant in high temperature and high pressure liquid flows into expansion valve. The refrigerant which used to flow in large space now passes through narrow area and its pressure drops as it goes. When the pressure drops, temperature drops dramatically as well. The cool refrigerant is now sent to an evaporator. Expansion valve are connected to sensible heat storage that detects heat. Sensible heat storage is installed on the exit of an evaporator and detects temperature Inside the storage is fluid sensitive to temperature changes and as the temperature at the exit of an evaporator rises, the gas pressure rises which in turn, presses on a spring to send more refrigerant to evaporator. When the amount of refrigerant going into evaporator surges, cooling emission surges too. When the temperature at the exit of an evaporator drops, gas pressure drops and the amount of refrigerant going into evaporator in turn,drops too. Applying the above principle, an air conditioner controls the amount of refrigerant injected into an evaporator to prevent over-cooling. A refrigerant passes through the pipes of an evaporator and takes away heat in this process. As the pan underneath starts to operate, warm air in the room is sent to an evaporator and cooled air is emitted.