A refrigerant is a fluid, ideally with a low boiling point and high latent heat of vaporization. It easily changes state from liquid to gas and in the process absorb heat from a surface and hence its use in refrigeration and air conditioning.
Two examples of refrigerants are Freon (R-22) and Puron (R-410A). Freon was however completely phased out in 2020 due to its contribution to global warming.
The function of a refrigerant in air conditioning is to absorb heat from the warm indoor air and release it to the outside/surrounding air. Its low boiling point and high latent heat of vaporization comes in handy in that regard.
A refrigerant is a gas at room temperature. To turn it into a liquid during air conditioning, it is first compressed and then sent out to a condenser coil. Inside the coils the refrigerant loses its heat (with the help of fan) to the surrounding to become a liquid.
A refrigerant cools a house by vaporizing. The cold liquid absorbs heat from the warm indoor air and due to its low boiling point it changes state to a gas/vapor. Thanks to its high latent heat of vaporization, it removes heat from the house in the process.
The very first air conditioners used chlorofluorocarbons as refrigerants. CFSs were later replaced by R-22 (Freon) but after R-22 was discovered to contribute to global warming R-410A (Puron) was established to be safe and is currently the most common refrigerant.
Types of Refrigerants
There are 3 main types of refrigerants. They are:
1. Chlorofluorocarbons (CFCs)
Chlorofluorocarbons are refrigerants that contain chlorine. Examples of CFC refrigerants are R11 and R12.
They were developed in 1928 in a bid to have refrigerants that were neither corrosive nor toxic but they turned out to be a disaster for the environment. Production of these refrigerants was stopped in 1994.
2. Hydrochlorofluorocarbons (HCFCs)
The difference between hydrochlorofluorocarbons and chlorofluorocarbons is that chlorofluorocarbons do not have a hydrogen atom in their structure. The extra hydrogen atom decreases the stability of hydrochlorofluorocarbons thereby reducing their lifetime in the atmosphere.
Nonetheless, HCFCs are still greenhouse gases with a very high global warming potential. An example of HCFCs is R-22 commonly known by its brand name, Freon.
The production of air conditioning systems using Freon was stopped in 2010 while the production of Freon itself was stopped in January of 2020. That was in line with the Montreal Protocol.
3. Hydrofluorocarbons (HFCs)
These are the refrigerants found in modern air conditioners. A common example of HFCs is R-410A, usually identified by its brand name, Puron.
Without a chlorine atom, HFC refrigerants are relatively safer for the environment. More studies however need to be carried out to ascertain if indeed these refrigerants have no effect on the environment and if they do, by how much.
Related: R-22 vs R-410A
Properties of a Good Refrigerant
- Low boiling point
- High latent heat of vaporization
- High critical temperature
- Low specific heat of liquid
- Low specific volume of vapor
How a Refrigerant Works in Air Conditioning
An air conditioning system is made up of 3 main components. The 3 components are:
- Condenser coil
- Evaporator coil
In central air and mini-split air conditioners, the evaporator coil is located inside the house while the compressor and condenser coil are found outside the house. Window and portable AC have all the components in one unit.
In this guide, I will focus more on the 2 main types of air conditioners that have an outdoor and an indoor unit.
The 3 components are connected together using copper tubes to form a closed-loop system. The refrigerant is then circulated through the 3 components where it changes state from gas to liquid and back to gas again as it removes heat from the house and releases it to the outside.
Let us now look at how a refrigerant works in each component:
1. Refrigerant inside the Compressor
In an air conditioning system, the refrigerant moves from the compressor to the condenser coil and then to the evaporator coil before going back to the compressor and the cycle goes on and on.
The refrigerant therefore enters the compressor, carrying heat from the evaporator coil inside the house. It is usually in its gas state but at a low pressure.
The function of the compressor as its name implies is to compress the gas thereby increasing its pressure. But why is it important to compress the refrigerant gas?
The idea is to remove the heat absorbed by the refrigerant to the outside. The only problem though is that that is usually during summer and the air outside would be hot as well.
Remember that in order for heat transfer to be effected, there needs to be a temperature differential. In other words, heat is transferred from a point of high concentration to one with a low concentration.
Luckily, an increase in the pressure of a fluid also results in an increase in its temperature. Compressing the refrigerant therefore increases its temperature way more than the outside temperature.
2. Refrigerant inside the Condenser Coil
The refrigerant enters the condenser coil as a high-pressure superheated gas. Due to the difference in temperature between the refrigerant and the surrounding air, heat can be transferred from the refrigerant to the surrounding.
A fan installed at the top of the condenser unit helps to accelerate this process. It blows air over the coil which absorbs heat from the refrigerant and takes it away.
By the time the refrigerant is exiting the condenser coil, it will have lost so much heat that it will have turned to its liquid state. That process is known as condensation.
3. Refrigerant inside the Evaporator Coil
The actual cooling of the house happens inside the evaporator coil. That is why this unit is located inside the house.
From the condenser coil, the refrigerant then enters the evaporator coil. Before that though, it is forced through an expansion valve.
An expansion valve is basically a restriction or in other words a small opening. First, this valve controls the amount of refrigerant entering the evaporator coil.
If too much of it enters the coil, not all of it will vaporize, meaning some will get to the compressor in its liquid state. A compressor is only designed to handle a refrigerant in a gas state hence it will be damaged.
Secondly, the expansion valve lowers the temperature of the refrigerant. You see, although the refrigerant is in its liquid state, it is not yet as cold as it needs to be.
The way an expansion valve lowers the temperature of the refrigerant is by reducing its pressure. When the refrigerant goes through the small opening, its pressure falls drastically.
As I had mentioned, an increase in pressure results in an increase in temperature. The opposite is also true.
When the refrigerant goes through the expansion valve, its temperature drops dramatically. From the expansion valve the refrigerant then enters the evaporator coil.
An evaporator coil has a fan which pulls warm air from the house and passes it through the coil. The refrigerant absorbs heat from the air and cools it in the process.
After absorbing enough heat from the indoor air and thanks to its low boiling point, the refrigerant vaporizes and exits the coil heading back to the compressor. The cycle is repeated over and over.
Actually, it is the process of vaporization that cools the house. Just like when you sweat. As the sweat evaporates, a cooling sensation is left on your skin.
Refrigerant Use in a Heat Pump
Heat Pumps are HVAC systems that work like conventional air conditioners when used to cool the house but the exact opposite when used to heat it.
As I had mentioned, during cooling, the refrigerant moves from the compressor to the condenser coil and then to the evaporator coil. When used for heating, the refrigerant in a heat pump moves from the compressor to the evaporator coil and then to the condenser coil.
That is made possible by the reversing valve. The reversing valve as it name implies reverses the direction of flow of the refrigerant when the cold winter months start.
Heat pumps extract heat from the surrounding by lowering the temperature of the refrigerant entering the condenser coil from the evaporator. Even when it is very cold outside, the heat pump can extract heat from the air.
The refrigerant is then compressed by the compressor resulting in a high-pressure superheated gas. The hot refrigerant enters the evaporator coil inside the house where the cold air absorbs heat from the refrigerant.
That is exactly how a heat pump heats your house even during winter.
And basically that is how a refrigerant works in air conditioning. I hope you enjoyed reading this post.