Refrigeration and Air Conditioning
Air conditioners and refrigerators are devices used to keep a space at a colder temperature than its surroundings. The main difference between refrigeration and air conditioning is that refrigeration, in general, refers to any process where thermal energy is taken away from a place and transferred to a place with a higher temperature.
Air conditioning is a type of refrigeration where thermal energy is taken away from the air (typically in a room or a vehicle) in order to keep the air cooler.
What is Refrigeration
Refrigeration refers to processes that take thermal energy away from a place and gives off that energy to a place with a higher temperature. Naturally, thermal energy flows from a place with a higher temperature to a place with a lower temperature. Therefore, refrigeration runs against the natural heat flow and so it requires work to be done. Refrigerator is a name that we use for devices that are used to keep food at low temperatures. A refrigerator consists of a fluid called refrigerant which gets expanded and compressed in a cycle:
- When refrigerant enters the compressor, the refrigerant is compressed adiabatically. This raises the temperature of the refrigerant.
- Then, the hot refrigerant is sent into the condenser under high pressure, which is typically a tube outside the refrigerator. Here, the temperature of the refrigerant is higher than the temperature of the surroundings. So, the refrigerant gives off heat to the surroundings and gets condensed into a liquid. If you touch the tubes at the back of a refrigerator, it feels hot because you are feeling the heat given out by the condenser.
- Next, the refrigerant goes through an expansion valve, where the pressure of the refrigerant is lowered. The refrigerant expands here, evaporating and cooling down.
- The refrigerant now enters the evaporator, which is a set of tubes inside the refrigerator. At this stage, the refrigerant is at a temperature lower than the temperature of the air inside the refrigerator. Now, the refrigerant draws in heat from inside the refrigerator. This is how heat is removed from inside a refrigerator.
Once the refrigerant goes through the evaporator, it is sent again into the compressor… and the cycle continues repeatedly.
What is Air Conditioning?
Air conditioning is a type of refrigeration where thermal energy is taken away from the air in a large space such as a room or a vehicle. Air conditioners are fitted into rooms so that they cool the air inside them. Air conditioners also reduce humidity in rooms, because the water vapor in the room can condense around the colder parts of the air conditioner. The condensed water can be then drained off.
Air conditioners work in the same way as refrigerators. The primary difference between an air conditioner and a refrigerator is that air conditioners are not only concerned with maintaining the temperature of the air; they also help to regulate humidity and filter the air. Air conditioners also consist of fans in order to circulate air, so that the hot air comes into contact with the evaporator at a faster rate.
Difference Between Refrigeration and Air Conditioning
Refrigeration is a process where thermal energy is transferred from a place with lower temperature to a place with higher temperature using energy, against he natural flow of heat.
Air conditioning is a type of refrigeration which is used to cool large volumes inhabited by people.
Refrigeration is concerned only with regulating the temperature of a volume of air.
Air conditioning is concerned with not only maintaining the temperature of a volume of air, but also maintaining he humidity and purity.
- An air conditioning system requires that the air is filtered and purified continually to remove odours and dust particles, using enzyme, mechanical and bio-filters. Refrigeration systems only require the same volume of air to be cooled and passed through the compartment in order to maintain the desired temperature.
- An air conditioning system demands the circulation of a certain volume of fresh air containing 20.9% O2. If fresh air is not provided, after a short time the O2 in the room’s atmosphere will be depleted and replaced with CO2. This makes it initially uncomfortable and then unsafe for human occupancy.
- The temperature in the refrigerator is very low to inhibit enzymatic action of the perishable items (thus facilitating its storage) whereas an air-conditioner provides temperature and humidity more favourable to human comfort.
- The control volume of a refrigerator is very limited for a specific size of compressor. But for the same size of the compressor an air-conditioner offers a much larger control volume.
- Convective Heat Transfer: Air movement is required for air conditioning in a closed room, as to keep the occupants cool the air needs to be circulated continually. In refrigerator, air movement is controlled by the temperature that is needed to be maintained (ie the demand temperature or thermostat set-point). Once the desired temperature is reached, the air movement simply stops.
The above list is the most prominent differences. I have excluded the finer working principles and the Psychrometry part.