How Do Refrigerants & Air-Conditioning Work?

Refrigerant and refrigeration is used across the world and every day in your daily life, but how does it work? This is a question that gets asked a lot by outsiders of the industry and it seems like most of the time it is hard to get an answer. Well folks, there’s a reason for that. It’s not a simple concept. It’s one of those things that if you look at it long enough something will click in your brain and it will all make sense. I’ll do my best here to document how these systems work and hopefully we can learn something together.

Refrigeration is all about absorbing and displacing heat from a room rather it be in a refrigerator, a freezer, or your home. The principal concept remains the same. In this example today we will be looking at your standard home air-conditioner. While this may not cover a refrigerator or your car’s air-conditioner you should note that the overall concept is the same.

Introduction

First and foremost let me tell you that your home air conditioner does not produce ‘cold air,’ in the same way that your furnace would produce heat. With a gas furnace you have the heat from the flame blowing into your home. Instead of that air-conditioners are all about transferring heat and changing states of the refrigerant. The refrigerant is used to absorb the heat from inside your home, carry that heat to your air-conditioner, and then release it to the outdoors. Once the heat has been removed the colder air blows back into your home. The refrigerant circulates continuously to remove additional heat from your home until your desired temperature is reached.

In order for a refrigerant to absorb heat a change of state has to happen. When I say change of state I am talking about going from liquid to gas and from gas to liquid. It is important to remember that the refrigerant cycle is just that, a cycle. That means that it goes over and over again. There is never any break to this cycle and should never be any leak in this cycle. It is a completely sealed process. Within this cycle there are different components that allow for the refrigerant to change pressure, temperature, and state. We will go over these as well as the process of the refrigeration system.

The Process & Components

Home AC Cycle

The picture above is a great illustration showing you how everything is laid out for a home air-conditioner. That being said, I will say that it does not label the components in order of process. But, that’s ok I will do that below for you. If you are unsure of what component I am referring to please consult the picture above to get an idea.

  1. Evaporator – The evaporator’s cooling coils remove the heat and humidity from the air inside your home using the designated refrigerant. Ever notice when your air conditioner kicks on and doors that were slightly ajar get ‘sucked’ close? That is your system pulling out hot air from your home.
  2. Suction Line – This is where the refrigerant is ‘sucked’ into the compressor. This is also known as the low pressure side.
  3. Compressor – The compressor is a pump that moves the refrigerant between the evaporator and the condenser to chill the indoor air. The compressor is often seen as the heart of the system. Instead of pumping and metering the blood flow to the rest of your body it pumps and meters the amount of refrigerant to the rest of the system. Upon entering the compressor the refrigerant is in a vapor state and as it’s name suggests the compressor’s job is to compress the vapor. When a vapor is compressed both the pressure and temperature of that vapor increases. The vapor leaving the compressor is VERY hot as a high temperature and high pressure vapor.
  4. Discharge Line – The high temperature vapor refrigerant then moves it’s way through the discharge line and into the condenser.
  5. Condenser – Upon entering the condenser the high temperature refrigerant air from a fan passes over the coil to cool the vapor refrigerant. As the vapor cools it undergoes a state change and changes into a liquid. At this point is where the hot air from inside your home is removed as the fan blows the air over the coils and outside of your home. If you ever stuck your hand over the top of your air-conditioner you would feel the hot air being blown out. That is your condenser at work.
    1. While in the condenser the refrigerant will begin to turn into a saturated state. A saturated state is where vapor and liquid both exist at the same time. The saturated state is where the majority of the energy is transferred. This is where the heat that the refrigerant is carrying is dissipated. At this point the refrigerant begins to absorb the heat and as it does it moves to liquid.
  6. Liquid Line – The high pressure liquid refrigerant moves it’s way through the liquid line and into the metering device. This point of the cycle is known as the ‘Subcool.’ If there is a problem with your system this is where most technicians start looking.
  7. Metering Device – The metering device’s purpose is to control the amount of liquid refrigerant that will be fed into the evaporator. Inside the metering device is a dividing point between high pressure and low pressure sides of the system. As the refrigerant is passed through the metering device the pressure drops.
  8. Evaporator Again – After leaving the metering device the low pressure liquid refrigerant immediately moves into the coils of your evaporator. Just like with the condenser the evaporator has a fan blowing against it’s coils. But this time instead of blowing hot air out of your home it is now blowing the cold air back into your home. Here is where big state change happens.
    1. As the refrigerant enters the coil at a lower pressure it begins to bubble and boil and as it does it begins to change state back into a vapor. (Same concept as boiling a pot of water and watching it all evaporate.) During this process of changing state from liquid to vapor the refrigerant is removing energy, or heat, from the air passing over the coils. The heat that was in the air is transferred into the refrigerant. Remember, it’s not about creating cold air but about removing the heat. Since the heat has been removed from the air when the fan blows over the evaporator’s coils cold air will blow into your home.
  9. Repeat – After this the whole process is started over again and again until your home has reached the desired temperature set on your thermostat.

 

Conclusion

While this is a difficult concept to understand I hope that I was able to help you today. If you walk away from this article with just a few things know this. All types of refrigeration work based off of state change. Vapor to Liquid and liquid to vapor over and over again. This constant change of states absorbs the heat and blows in cold air. It’s that simple!

Thanks for reading,

Alec Johnson

RefrigerantHQ

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