What is Hermetic, Semi-Hermetic and Open Compressors?

In the history of commercial compressors, several different technologies have emerged. The earliest commercial compressors were typically of the reciprocating type, which was later followed by the screw compressor. The screw compressor was designed to overcome the engineering limitations and challenges of the reciprocating model.

Today, most commercial compressors are either reciprocating or screw-type. Only the largest commercial compressors rely on centrifugal force as their primary operating principle. However, there is another important factor to consider when choosing a compressor: the underlying architecture of the compressor technology. This dimension can play a significant role in determining the best option for your needs.

There are three main compressor architectures:

- Hermetic

- Semi-Hermetic

- Open

Reciprocating compressors, screw compressors, and other types can be designed using any of these three architectures. Each approach is typically associated with specific technologies and applications, and the choice of architecture will significantly affect your system's performance.

Once a compressor is chosen and installed, it can be difficult to "start over," making the initial selection crucial. When dealing with large-scale refrigeration or HVAC systems, the "right choice" is always one that is informed, ensuring optimal performance and efficiency for the long term.

What Is a Hermetic Compressor?

Hermetic compressor describes a style of compressor you are less likely to see in large industrial or commercial applications, but it is still used on occasion. A hermetic compressor is completely sealed away from the environment, with the casing welded shut. It cannot be accessed by any means.

In general, "hermetic" refers to an airtight seal. In the context of compressors, it means the compressor is completely sealed off from the external operating environment. This design prevents issues such as spillage or debris infiltration, reducing the risk of flooding and slugging.

However, hermetic compressors have some significant limitations, particularly in demanding environments. They are typically used in smaller systems and are more commonly found in consumer goods, such as home refrigerators.

In business settings, hermetic compressors are often seen in small refrigerated displays at grocery stores. These units can be "chained together" to ensure functionality even if one compressor underperforms or fails. The compact, lightweight design of hermetic compressors makes them ideal for this purpose.

Despite their advantages in certain applications, hermetic compressors are often overlooked for situations that require high performance and efficiency. One of the major drawbacks is that they cannot be serviced if a mechanical issue arises. Even if the problem is minor, the only solution is usually to replace the entire compressor.

What Is a Semi-Hermetic Compressor?  

A semi-hermetic compressor, like a hermetic one, features both the compressor and motor fully enclosed within a sealed shell, protecting them from the external environment. However, unlike hermetic compressors, semi-hermetic models are designed to be opened for diagnosis and routine maintenance.  

Maintenance plays a crucial role in extending the service life of a compressor, ultimately saving significant costs over time. While no compressor lasts forever, modern models can operate at peak efficiency for years if properly maintained.  

Thanks to its serviceability and reliability, the semi-hermetic compressor has become the preferred choice for most applications, even replacing other options, including smaller reciprocating units that were traditionally hermetic.

What Is an Open Compressor?  

In an open compressor, the motor and compressor are not shielded from the external environment. While these compressors can be serviced, they require a carefully controlled environment to prevent failure due to dirt, debris, chemicals, and other contaminants. Without proper care, the risk of damage is significantly higher.

What Type of Commercial Compressor Should You Use?

If you have the option to choose between a hermetic and semi-hermetic compressor with the same performance specifications, it’s generally a good idea to opt for the semi-hermetic compressor. This type allows for easier maintenance and repairs, helping to minimize downtime. Be sure to keep the necessary spare parts on hand to quickly address any issues that may arise.

If a hermetic compressor is required for your application, consider reducing your reliance on a single unit. Having a backup commercial compressor ready can help mitigate the impact of any potential failures.

Choosing a remanufactured commercial compressor can also be a cost-effective solution. These units can match the performance and longevity of new OEM products, often costing 10%, 20%, or even 30% less. Additionally, they may be available sooner, which can be crucial in time-sensitive situations.

Regardless of the compressor type or architecture you choose, working with a remanufacturing team ensures you get the most value and the longest lifespan from your equipment.