Refrigeration Theory: Chapter 2
In this module, we will go over the refrigeration cycle and how it works to provide cooling. We will use the concepts we talked about in the previous module to understand this. The refrigeration cycle is what makes your air conditioning, refrigerator, or any other refrigeration system work. Skip to quiz!
1. How Does the Refrigeration Cycle Work?
In your daily life, you are likely surrounded by comforts made possible by the refrigeration cycle — especially during the hot summer months. The refrigeration cycle is what powers your air conditioning unit and, on a smaller scale, your refrigerator.
As mentioned in the video, air conditioning works by absorbing heat from your indoor air and ejecting it outdoors. It uses a refrigerant to do this. A refrigerant is usually a liquid used in refrigeration systems to absorb heat.
Think of a vacuum. With a vacuum, we capture dust and dirt and move them to the trash. This is the same concept. But instead of capturing dirt, we are capturing heat and moving it outdoors.
It does this by passing a refrigerant with a low boiling point through a series of coils that come in contact with warm indoor air. Recall that a boiling point is a temperature at which liquid turns to vapor.
In the refrigeration cycle, we use refrigerants with low boiling points. Because refrigerants have lower boiling points, they will boil at a lower temperature than your indoor temperature on a hot day. This is so that your indoor air is hot enough to make the refrigerant boil.
For example, a hot summer day would be around 90°F. A typical refrigerant, R-134a, has a boiling point of -15.34°F! Since the hot summer air is above the boiling point of the refrigerant, the refrigerant would boil at that temperature.
The most commonly used refrigeration system is called the direct expansion vapor compression system. For example, this type of system is found in both your air conditioning as well as your refrigerator.
Direct expansion systems are systems where the cooling effect comes from the expansion of a liquid to a vapor. If we think about water vaporizing to steam, the steam rises up and fills the air. This is the “expansion” behavior of vapors.
2. Vaporization
As the refrigerant boils, it changes state from liquid to vapor. As mentioned in the previous module, this process is also called vaporization, as the refrigerant is changing from liquid to vapor.
Recall that during vaporization, or boiling, you need to add continuous heat until all liquid has changed state to vapor. The heat that is needed to change the phase is called latent heat.
Think about boiling a pot of water. You apply heat to it by turning on the stove, which increases the temperature of the water. Once the water reaches its boiling point, it starts to bubble and turn into steam, which leaves the pot and dissipates into the air.
If you keep the stove on, you are continuously applying heat to water that is already at its boiling temperature. More and more water molecules will become steam, which is also known as water vapor.
If you turn off the stove after the water starts to boil, what’s left of the water will stop boiling and remain in the pot. This demonstrates that you need to continuously apply heat in order for all of the water to become vapor.
If the stove is left on, the water in the pot will decrease until all the water eventually turns to vapor. You’ve probably seen this if you’ve accidentally left the stove on too long. Either the pot has completely dried up or there’s much less water than before. This is because water has changed state into vapor.
In the refrigeration cycle, instead of water, you have refrigerant boiling. And instead of a stove flame, it is the hot indoor air that is providing heat for refrigerants to completely boil. This process is what draws heat away from your indoor air and provides cooling.
To reiterate, it is the boiling or vaporization of refrigerant that provides cooling in a refrigeration system. This is similar to the example mentioned in the video, where if you have water on your body, you will feel cold as it evaporates.
As the refrigerant moves through the refrigeration cycle, it effectively transfers heat from inside the house to outside the house.
3. Conclusion
In the refrigeration cycle, the refrigerant absorbs heat from your indoor air by using that heat to boil, changing the state from liquid to vapor. We choose refrigerants with a low boiling point in order for this to happen.
The refrigeration cycle is what powers cooling in your air conditioning system or refrigerator. Next, we’ll go into more detail about the components of the refrigeration cycle and what happens in each component.
Question #1: A refrigerant is a substance that
Adds cool air to your house
Absorbs heat to provide cooling
Absorbs cool air to transfer it
All of these
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Answer: Absorbs heat to provide cooling
A refrigerant’s job in refrigeration systems is to absorb heat. By absorbing heat, it provides cooling. It does not add cool air (a) or absorb cool air (c).
Question #2: The boiling point of a refrigerant is similar to that of water because they are both liquids.
True
False
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Answer: False
This is false. We know that the boiling point of pure water is 212 °F or 100 °C. The boiling point of a refrigerant has to be less than room temperature in order for it to work and room temperature is around 68-72°F. So their boiling points are not similar.
Question #3: Refrigerant absorbs heat from your indoor air in order to (Select all that apply)
Change state from vapor to liquid
Change state from liquid to vapor
Make your house cooler
Evaporate into the air
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Answer: Change state from liquid to Vapor
Make your house cooler
The refrigerant absorbs heat from your hot indoor air in. This is what makes your house cooler. As the temperature of the refrigerant increases, it changes state from vapor to liquid.
Question #4: If refrigerant boils at __, that means it will completely change phase to vapor at room temperature (which is 68-72°F).
-10 °F
80 °F
212 °F
All of these
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Answer: -10 °F
We know that refrigerants have boiling points that are below room temperature. The only temperature below room temperature on this list is -10°F.
Question #5:Your air conditioning works by adding cold air into your house.
True
False
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Answer: False
This is false. Your air conditioning works by absorbing heat from your indoor air, not by adding cold air.