What is a Hermetic Compressor? Understanding the Basics

Figure 1: Danfoss reciprocating compressor.

When it comes to refrigeration systems, a crucial component is the compressor. This is the part that compresses the refrigerant and moves it through the system, allowing for heat transfer and ultimately creating the cooling effect.

One type of compressor that is commonly used in refrigeration and air conditioning applications is the hermetic compressor (hermetically sealed compressor). It is called "hermetic" because the motor and compressor are enclosed in a single, welded steel shell.

In this article, we'll take a closer look at what a hermetic compressor is (hermetic compressor definition), how it works, its advantages and disadvantages, and its applications.

1. What is a Hermetic Compressor?

A hermetic compressor is a type of compressor that is completely sealed from the outside environment. The motor and compressor are enclosed in a single, welded steel shell that is designed to prevent any leaks or contamination from entering the compressor.

This shell is often made of steel or aluminum and is designed to be completely airtight, hence the term "hermetic." The hermetic design eliminates the need for external shaft seals or bearings, which can be a source of leaks and maintenance issues.

Figure 2: Hermetic reciprocating compressor diagram.

2. Main Types of Hermetic Compressor

● Hermetic Reciprocating Compressors: Reciprocating compressors are the most common type of hermetic compressor. They work by using a piston that moves back and forth inside a cylinder to compress the refrigerant.

As the piston moves up and down, it creates a vacuum on the intake stroke, which draws in the refrigerant. Then, as the piston moves up on the compression stroke, it compresses the refrigerant and pushes it out of the compressor.

● Hermetic Rotary Compressors: The rotary compressor, that is rolling piston compressor, works by using a roller with a vane that slides in and out of the slot in the rotor. As the rotor turns, the vane moves in and out, creating a vacuum on the intake side and compressing the refrigerant on the discharge side.

● Hermetic Scroll Compressors: Scroll compressors use two interleaved scrolls to compress the refrigerant. As the scrolls rotate, they trap and compress the refrigerant between them.

● Hermetic Screw Compressors: Screw compressors use two rotating screws to compress the refrigerant. As the screws turn, they compress the refrigerant and move it through the compressor.

Regardless of the type of hermetic compressor, they all share the same basic design of being completely sealed within a metal casing, or shell. This makes them a popular choice for refrigeration and air conditioning applications where airtightness is critical, as it reduces the risk of refrigerant leaks.

Figure 3: Hermetic scroll compressor and rotary compressor.

3. How Does a Hermetic Compressor Work?

Hermetic compressors work by using a motor to drive a piston or scroll that compresses refrigerant gas. The basic operation of a hermetic compressor is similar to that of other types of compressors.

It begins with the refrigerant entering the compressor through the suction line. The compressor then compresses the refrigerant, raising its temperature and pressure. The high-pressure refrigerant then moves through the discharge line and into the condenser, where it releases heat and condenses back into a liquid.

Figure 4: The structure and working principle diagram of the scroll compressor.

4. Advantages of Hermetic Compressors

In addition to their airtight design, hermetic compressors offer several other advantages over other types of compressors. These include:

● Lower Cost: Hermetic compressors are typically less expensive than other types of compressors, such as semi-hermetic or open drive compressors. This is because they are simpler in design and require fewer components.

● Easy Maintenance: Hermetic compressors are designed to be maintenance-free. Since they are sealed, there are no moving parts that need to be lubricated or maintained. This can save time and money on maintenance costs.

● Compact Size: Hermetic compressors are generally smaller and more compact than other types of compressors. This can be an advantage in applications where space is at a premium, such as in residential or commercial air conditioning units.

● High Efficiency: Hermetic compressors are highly efficient and can deliver high volumes of compressed refrigerant gas with relatively low energy consumption.

● Quiet Operation: Hermetic compressors operate quietly because the motor and compressor components are completely enclosed.

● Easy installation: Hermetic compressors are easy to install because they come as a complete unit that can be mounted directly onto the refrigeration or air conditioning system.

Figure 5: Maneurop hermetic compressor unit.

5. Disadvantages of Hermetic Compressors

While hermetic compressors offer several advantages, there are also some potential disadvantages to consider. These include:

● Limited Capacity: Hermetic compressors are generally limited in terms of their capacity. This means that they may not be suitable for larger-scale refrigeration or air conditioning applications.

● Limited Serviceability: Since hermetic compressors are designed to be sealed, they are not easily serviceable. If a problem arises, it may be necessary to replace the entire compressor unit rather than repairing it.

● Limited durability: Hermetic compressors may not be as durable as semi-hermetic or open compressors because they are not designed to withstand heavy use or harsh environments.

6. Applications of Hermetic Compressors

Figure 6: Hermetic refrigeration compressor applications.

Hermetic compressors are used in a wide range of refrigeration and air conditioning applications, including:

● Residential Air Conditioning: Hermetic compressors are commonly used in residential air conditioning systems.

● Commercial Refrigeration: Hermetic compressors are used in commercial refrigeration systems, such as those found in grocery stores and restaurants.

● Transportation Refrigeration: Hermetic compressors are used in refrigerated trucks and trailers to transport perishable goods.

● Medical Refrigeration: Hermetic compressors are used in medical refrigeration systems, such as those used to store vaccines and other medications.

The hermetic design makes hermetic compressors a good choice for applications where refrigerant leaks can be especially problematic, such as in food storage or medical facilities.

7. Conclusion

Hermetic compressors offer many advantages over other types of compressors, including low maintenance, high efficiency, compact design, and quiet operation. However, they also have some disadvantages, such as limited serviceability and environmental concerns. Overall, hermetic compressors are an important component of refrigeration and air conditioning systems, and their unique design allows them to be used in a wide range of applications.

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