What is a Semi-Hermetic Compressor? Everything You Need to Know

BITZER semi-hermetic refrigeration compressor unit on display

Figure 1: BITZER semi-hermetic compressor unit.



If you're in the refrigeration or air conditioning industry, you may have come across the term "semi-hermetic compressor." But what exactly is a semi-hermetic compressor, and how does it differ from other types of compressors?

Unlike hermetic compressors, which are completely sealed units, semi hermetic compressors have a removable cover that allows for maintenance and repair. In this article, we'll take a closer look at what a semi-hermetic compressor is, how it works, and its advantages and disadvantages.

1. What is a Semi-Hermetic Compressor?

A semi-hermetic compressor is a type of compressor used in refrigeration and air conditioning systems. It is called "semi-hermetic" because the compressor's motor and compressor housing are enclosed in a single, sealed unit. Unlike a hermetic compressor, which has the motor and compressor enclosed in a single, welded steel shell, a semi-hermetic compressor has a removable cover that allows for servicing and maintenance.

Semi hermetic compressors are commonly used in commercial and industrial refrigeration systems, where reliability and durability are critical.

2. Main Types of Semi-Hermetic Compressors

Semi-hermetic compressors are a type of compressor that combines some of the features of hermetic and open-drive compressors. There are several main types of semi-hermetic compressors, including:

● Semi-Hermetic Reciprocating Compressors: Reciprocating semi-hermetic compressors work in the same way as reciprocating hermetic compressors, using a piston to compress the refrigerant. However, the motor and compressor components are not completely sealed, and can be accessed for maintenance or repair.

● Semi-Hermetic Screw Compressors: Screw semi-hermetic compressors use two rotors that mesh together to compress the refrigerant. Like reciprocating semi-hermetic compressors, they can be serviced or repaired, but they are typically used in larger applications where higher capacity is needed.

● Semi-Hermetic Scroll Compressors: Scroll semi-hermetic compressors use two interleaved scrolls to compress the refrigerant. Like screw semi-hermetic compressors, they are typically used in larger applications, and can be serviced or repaired.

3. How Does a Semi-Hermetic Compressor Work?

BITZER high/low temperature cold storage semi-hermetic water-cooled compressor section

Figure 2: BITZER semi-hermetic compressor section.



Semi hermetic compressors work by using a motor to drive a piston or scroll that compresses refrigerant gas. Here take the semi-hermetic reciprocating compressor as an example to introduce the working principle of a semi-hermetic compressor.

The basic design of a semi-hermetic compressor consists of a motor, a crankshaft, a piston, and a cylinder. The motor drives the crankshaft, which in turn drives the piston up and down in the cylinder. As the piston moves up and down, it compresses the refrigerant gas that flows into the cylinder, raising its pressure and temperature.

The operation of a semi-hermetic compressor can be broken down into four stages: suction, compression, discharge, and cooling.

3.1 Suction

During the suction stage, the refrigerant gas enters the compressor through the suction line. As the piston moves down in the cylinder, it creates a vacuum that draws the refrigerant gas into the cylinder.

3.2 Compression

During the compression stage, the piston moves up in the cylinder, compressing the refrigerant gas and raising its temperature and pressure.

3.3 Discharge

During the discharge stage, the compressed refrigerant gas leaves the compressor through the discharge line and flows into the condenser.

3.4 Cooling

During the cooling stage, the compressor is cooled by the refrigerant gas flowing through it. The refrigerant gas absorbs the heat generated by the compressor, which is then dissipated by the condenser.



the inner structure diagram of semi hermetic compressor

Figure 3: Semi hermetic compressor diagram.

4. Advantages of Semi-Hermetic Compressors

Semi-hermetic compressors offer several advantages over other types of compressors:

● Easy Maintenance: Semi-hermetic compressors are designed to be easy to maintain and repair. The removable cover allows technicians to access the internal components of the compressor without having to replace the entire unit.

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

● Durability: Semi-hermetic compressors are designed to withstand harsh environments and heavy use, making them ideal for commercial and industrial applications.

● Versatility: Semi-hermetic compressors can be used in a wide range of refrigeration systems, from small commercial units to large industrial systems.

5. Disadvantages of Semi-Hermetic Compressors

Semi-hermetic compressors also have some disadvantages, including:

● Cost: Semi-hermetic compressors are more expensive than reciprocating compressors, as they require more precise manufacturing and assembly.

● Maintenance: While semi-hermetic compressors can be serviced and maintained, they still require more maintenance than hermetic compressors. The removable cover can also be a point of failure if it is not properly installed or if the gasket fails.

● Noise: Semi-hermetic compressors are generally louder than hermetic compressors, as the motor and compressor components are not completely enclosed.

● Limited Access: While the removable cover allows for easy maintenance and repair, it also limits access to certain components of the compressor.

● Larger Size: Semi-hermetic compressors are larger than hermetic compressors, making them less suitable for applications where space is limited.



Copeland semi-hermetic compressor on the wooden support

Figure 4: Copeland semi-hermetic compressor.

6. Applications of Semi-Hermetic Compressors

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

Supermarkets: Semi-hermetic compressors are commonly used in supermarket refrigeration systems, where reliability and efficiency are critical.

Food Processing Plants: Semi-hermetic compressors are used in food processing plants to maintain proper temperature and humidity levels.

Cold Storage Facilities: Semi-hermetic compressors are used in cold storage facilities to maintain the desired temperature and prevent spoilage of goods.

Industrial Cooling Systems: Semi-hermetic compressors are used in industrial cooling systems, such as those used in manufacturing and chemical processing.

Air conditioning: Semi-hermetic compressors are used in air conditioning systems, particularly in larger commercial and industrial buildings.

7. What is the Difference between a Hermetic and a Semi-hermetic Compressor?

Bitzer hermetic scroll compressor (left) and semi-hermetic piston compressor (right)

Figure 5: Bitzer hermetic scroll and semi-hermetic piston compressors.



A hermetic compressor is a sealed unit where all of the internal components are enclosed and cannot be accessed for maintenance or repair. In contrast, a semi-hermetic compressor has a removable cover or shell that allows for maintenance and repair of the compressor without having to replace the entire unit.

The semi-hermetic design makes these compressors more serviceable but also more expensive than hermetic compressors.

Semi-hermetic compressors are commonly used in commercial and industrial refrigeration systems, while hermetic compressors are typically used in smaller residential and commercial applications.

8. Conclusion

OKmarts is a professional company specializing in offering various industrial parts, such as refrigeration compressors, fans, valves. Different sizes and models of Copeland semi hermetic compressors and semi hermetic Bitzer compressors are available on our websites. If you are interested in these products, please feel free to contact us. Our experienced salesmen can find the product you want.

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