How Refrigerants Work In HVAC Systems
In order for a refrigerant to be effective, the thermal energy must be moved around the air conditioning or HVAC system. This is true for every kind of refrigeration system including an industrial unit, a small air conditioning unit and the refrigerator in a home kitchen. All of these units work the same way. A refrigerant is passed between the main components of the evaporator, expansion device, condenser and cooler to take the unwanted heat from a specific location such as a home or office and send the heat outside. This process is how the HVAC cools down the building.
The Boil and Evaporate of the Refrigerant
The term refrigerant refers to a fluid that can be easily boiled. This turns the refrigerant from a liquid into a vapor. The refrigerant can also be condensed to return back to a liquid form from a vapor. To be effective, this process must occur continuously over and over again. Water is a good example of a refrigerant. This is because water is safe and easy to use and is able to both evaporate and condense. Water is often used as a refrigerant in Absorption chillers because it is effective and safe for this purpose. The reason water is not commonly used as a refrigerant for air conditioning units and HVAC systems is because refrigerants are created specifically for this purpose. This type of refrigerant is able to perform with a lot more efficiency than water.
The Boiling Points and Types of Refrigerants
An HVAC App may help determine the type of refrigerant the HVAC requires. Some of the most common refrigerants currently available include R410A, R134A and R22.
It is important to note the regulations and laws regarding refrigerants are tightening. It is possible many of the current refrigerants will be phased out completely as time passes. One commonality between all of these refrigerants is their boiling point is extremely low in comparison to water. This means it does not require nearly as much thermal energy for the refrigerant to evaporate and become a vapor. This enables the refrigerant to extract heat a lot faster.
The Way a Compressor Works
The way the refrigerant is able to move around the HVAC system begins with the compressor. This is because the compressor is the heart of the entire HVAC system. This forces the refrigerant to move around all of the components contained in the refrigeration system. When the refrigerant initially enters, it is a saturated vapor with low pressure and a low temperature. As the refrigerant is pulled in by the compressor, it is rapidly compressed. The molecules are then forced together so they are able to fit into a much smaller area.
These molecules are always bouncing around. Once they have been compressed into a smaller area, they start colliding with each other more frequently. These collisions convert this kinetic energy into heat. While this is happening, all of the energy the compressor put in is being converted into internal energy being used by the refrigerant. The end result is an internal pressure, temperature, enthalpy and energy increase of the refrigerant. The principle is very similar to using a bike pump. As the pressure increases, the pump becomes extremely hot.
The Way a Condenser Works
The next step is when the refrigerant moves to the condenser. The condenser rejects all the undesirable heat right out into the atmosphere. This includes all the heat inside of the compressor in addition to the heat from the building. The refrigerant must be at a higher temperature when it enters the condenser than the surrounding ambient air or the heat will not be able to transfer. The larger the difference in temperature, the easier it is for the heat to transfer. The refrigerant is a superheated vapor when it enters at a high temperature and pressure.
The refrigerant then passes along the condenser tubes. As this is happening, air is blown across the condenser by fans to remove the undesirable energy when in a system cooled by air. This is a lot like blowing on a hot cup of coffee to help it cool down. The heat is removed from the refrigerant as the air is blown across the tubes. Once the refrigerant begins giving up the heat, it is condensed into a liquid form. This means when the refrigerant does leave the condenser, it has become a saturated liquid. The liquid remains at a higher pressure, but it has decreased in both entropy and enthalpy as well as being slightly cooler.
The Way the Evaporator Works
The process then carries the refrigerant to the expansion valve. The flow of refrigeration is measured by the expansion valve as it enters the evaporator. A good example would be a thermal expansion valve. This type of valve holds back the refrigerant and creates both low and high-pressure sides. The valve then makes adjustments to enable some of the refrigerants to flow. This refrigerant will become part vapor and part liquid. As the refrigerant passes through, it expands in an attempt to fill the void. The expansion causes a reduction in temperature and pressure for the refrigerant. This is very similar to holding a spray can. When the trigger is held down, the refrigerant is able to escape from the expansion valve at a low temperature and pressure prior to heading directly into the evaporator.
The refrigerant is received by the evaporator prior to another fan blowing the warm air from the room across the coils of the evaporator. Since the temperature of the air in the room is greater than the refrigerants cooler temperature, it is able to absorb a lot more energy. The refrigerant can then be boiled completely until it turns into a vapor. When a pan of water is heated, the water evaporates due to the heat. The water becomes a steam vapor capable of carrying away the heat. The refrigerant process is very similar. If the hand were placed directly over the rising steam, it would feel extremely hot and could be burned. The boiling point of a refrigerant is low, so it can be boiled into a vapor just through the temperature of the air in the room.
The refrigerant is at a low temperature in the form of a low-pressure vapor when it leaves the evaporator. Many people are confused because there is only a slight change in temperature. The reason the temperature does not dramatically increase is that it went through the change from being a liquid to become a vapor. This means the bonds located between the molecules were broken by the thermal energy. The entropy and enthalpy have increased and this is where the energy goes. Once the fluid has stopped changing, the temperature will no longer change. All of this is the basics of the way refrigerants perform in an HVAC system and how they are able to effectively cool the home or office.
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