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Overview of Screw vs Centrifugal Compressor in HVAC

Views: 213     Author: Site Editor     Publish Time: 2024-01-26      Origin: Site


There are two major compressors you can depend on for large volume of air. They are: screw compressor and centrifugal compressor. Even though they are both used for the same category of demand, these two have their uniqueness and expertise; they cannot replace each other.


They will certainly coexist for a long time. Therefore, it’s imperative to compare their performances and peculiarities in order to have solid references when choosing the preferred air compressor that fulfills your needs.


Types of Air Compressor




When choosing, many factors come into play, such as air quality, energy efficiency, size, lifespan, capacity, noise, costs, maintenance, and ideal application. In this post, we will discuss which compressor between screw vs centrifugal compressor ticks your boxes.


Overview of Screw Compressor

The idea behind screw compressors can be traced back to the early 20th century when German engineer Heinrich Krigar created the first twin-screw compressor. But it took until the 1950s before the compressor was properly manufactured. The delay was due to insufficient technology and the unavailability of quality materials for the accomplishment of the idea behind the compressor structure.


In the 1960s, different companies started producing screw compressors for various industrial applications, including refrigeration and air conditioning purposes. During this period, oil-injected screw compressors were created. Using oil as lubricant improved the compressors efficiency and extended their lifespan.


Today, screw compressors have marked their stand as one of the most reliable HVAC types of compressors, thanks to their reliability and efficiency.


What is a Screw Compressor?


This is a common type of positive displacement compressors i.e, compressor types that mechanically trap a fixed amount of air and reduce its volume to increase pressure, so as to provide a continuous and controlled airflow.



A Screw Compressor



A scroll compressor features two helical rotors (male and female) that are mesh closely, but don’t touch each other. When working, the rotors spin in opposite directions, and as they spin, they compress the air trapped between them. This compressor offers a steady and pulsation-free airflow.


Furthermore, screw compressors are popularly revered for their low maintenance requirements and reliability in situations that demand continuous flow of air. They are often produced in two kinds: oil-injected and oil-free, thereby providing suitable options for cleanroom applications like the pharmaceutical industry.


Overview of Centrifugal Compressor


Centrifugal compressor was ideated a long time ago, as far back as 1689, with the collaboration of French physicist Denis Papin and Dutch physicist Christian Huyghens. They experimented with an air compressor, using centrifugal force to achieve the compression process.


Thanks to advancement in the physics community with better understanding of fluid and thermal dynamics, the centrifugal compressor system was developed from using a crude single impeller blower into the multi-stage system used today.

With growing emphasis on energy efficiency, centrifugal compressors are integrated with improved control systems and play an important role in energy-efficient industrial processes.


What is a Centrifugal Compressor?


This is a common type of dynamic compressors i.e., compressor types that use kinetic energy conversion through the high-speed rotation of an impeller to increase air compression dynamically.


A Centrifugal Compressor



A centrifugal compressor is a mechanical device constructed to compress air through centrifugal force. It features a few essential components that work harmoniously to efficiently compress air. At the core is the impeller that imparts kinetic energy to the absorbed air. The high-velocity air then passes through a diffuser, where the kinetic energy is changed into potential energy due to an increase in pressure.


Centrifugal compressors are popularly revered for their suitability for applications that require dynamic and variable airflow. Also, these compressors are designed to be oil-free. The airflow path and the oil system are constructed to be in different sections; seals separate them.


Hence, they are most ideal for applications where uncontaminated air is needed, such as food & beverage, pharmaceuticals, and manufacturing industries.


Centrifugal Compressor vs Screw Compressor: Working Principle

Despite the fact that centrifugal and screw compressors are both used for large volume of air, their working principle differs.


How does a Centrifugal Compressor Work?

The working principle of a centrifugal compressor begins with the rotation of the impeller, which is connected to the compressor shaft that an external driver like an electric motor or turbine usually powers.


Air is absorbed into the compressor through the inlet valve. As the impeller spins, it gives kinetic energy to the absorbed air by increasing it radially outward due to centrifugal force.


After that, the high-velocity air leaves the impeller and goes to the diffuser, where the kinetic energy will be converted to potential energy, resulting in a significant increase in pressure.


Then, the air exits the diffuser and flow into a stationary volute casing that guides it towards the outlet valve while maintain the pressure.


How does a Screw Compressor Work?


The working principle of a screw compressor is quite simple. It involves the spinning of the two intermeshing rotors. Another compressor that has a similar working principle is the scroll compressor. Hence, why there is often a comparison between scroll vs screw compressor.


Screw compressor rotors are precisely designed and machined to mesh closely. However they don’t touch each other; rather, they move in opposite directions.


As they begin to rotate, the compressor absorbs air through an inlet valve. With the continued spinning, the rotors begin to decrease the space between them, causing the air to compress. After that, the compressed air is pushed to the midpoint of the rotors, where it exits the compressor through a discharge port attached to the end of the rotors.


For the oil-injected screw compressors, oil is applied to the compression chamber to serve as lubrication on the moving parts. The oil doesn’t just serve as lubricant, it stops air from leaving the compression chamber.


Design Difference between Screw vs Centrifugal Compressor


The structural design of screw and centrifugal compressors is the major factor that influences the differences that exist between these two reliable compressors.


Centrifugal compressors have an intricate design, involving the connection of the key components to one another. Firstly, the impeller is linked directly to the shaft, which is guided by suction valves, bearings, and seals for stability and prevention of air leakage. Then, there is the inlet that allows ambient air to enter, passing through the impeller to the diffuser, which converts kinetic energy to potential energy. Lastly, the diffuser is linked to the outlet part that distributes the compressed air for use.


Centrifugal Compressor Design Structure



Screw compressors consist of two helical rotors (male and female) that intermesh closely, and rotate in opposite directions. The rotors are encapsulated within a cylindrical casing, with inlet and outlet ports for entry and exit of air. They also have other main parts like the bearings and cooling jacket.


Screw Compressor Design Structure


Screw Compressor vs Centrifugal Compressor Pros and Cons

Screw compressor vs centrifugal compressor can also be differentiated based on their pros and cons.


Screw Compressor


Pros

● Ideal for a wide range of applications and compression ratios

● Provides continuous and steady flow of air

● Energy-efficient with good part-load performance

● Suitable for smaller industrial applications


Cons

● Require more frequent maintenance compared to centrifugal compressor

● Less-effective for extremely high-speed operations

● Oil contamination concerns when using oil-injected screw compressors


Centrifugal Compressor


Pros

● Perfect for high-speed and dynamic applications

● Capable of handling variable airflows

● Require less frequent maintenance compared to screw compressor

● Suitable for larger industrial applications


Cons

● Complex design structure with many intricate parts

● High manufacturing cost

● Produce louder noise and vibration


Centrifugal Compressor vs Screw Compressor on Performance

There are many factors behind the difference between centrifugal compressor vs screw compressor. Below, we will compare these two compressors and see their overall performance.


● Air Quality


When using air quality as a parameter to compare centrifugal vs screw compressor, it’s essential to look into the solutions they are catering to.


Centrifugal compressors have departmental design, as there are many parts in the construction, and each of them has unique functions. The oil lubrication part is different from the compression section, which ensures that the air is not contaminated. Generally, centrifugal compressors are known for their dynamic and high-speed operation, which ensures smoother compression and lower oil carryover.


Centrifugal Compressor



Screw compressors are available in two kinds: oil-free options and oil-injected options. The oil-free types don’t use oil lubrication, guaranteeing that the compressed air is clean and free from contaminants. However, the oil-injected types often produce compressed air with oil carryover.



● Energy Efficiency

Screw compressor vs centrifugal compressor efficiency is primarily dependent on the operational conditions.


Screw compressors are most energy-efficient when used in part-load operational conditions, hence why they are best-suited for applications that have varying air demand, including low temp heat pumps. They are very reliable in handling start-stop cycles.


Centrifugal compressors, on the other hand, are most energy-efficient when used in full-load operational conditions, hence why they are best-suited for applications that require constant high-speed airflow. They are very reliable in handling scenarios with stable and predictable air demand.


● Costs

Just like any equipment, it’s imperative to be aware of the cost difference of screw compressor vs centrifugal compressor.


Screw compressors have lesser initial cost due to their simple design construction and fewer parts compared to centrifugal compressors. However, they have higher running costs because their operation mechanism involves more moving parts, which results in frequent maintenance and repairs.


Centrifugal compressors, on the other hand, have high initial cost, particularly because of the complexity of the construction and intricacy of the design. However, they have fewer moving parts, resulting in lesser maintenance and repairs.


● Size

A rotary screw vs centrifugal compressor comparison won’t be complete without mentioning their size variation and how it affects their functionality.


Rotary screw compressors have a simple, compact design, which is very beneficial in installations with limited space. Their size allows for flexibility, ensuring easy adaptation to varying spatial constraints. However, in larger capacity applications, screw compressors are not always the best because their design structure limits their ability.


While centrifugal compressors have a more complicated design structure. Their construction allows scalability for increased capacity, thereby are best used for applications with more extensive spatial requirements. Additionally, centrifugal compressors are often associated with larger industrial applications due to their efficiency in handling higher air volume.


● Stability and Durability

Both compressors demonstrate resilience, but there are certain factors that can be used to differentiate screw vs centrifugal chiller in this regard.


Screw chillers are known for their robust design, and when properly maintained, offer good stability and durability. Carrying out regular maintenance practices like lubrication and inspections can also extend their lifespan.


While centrifugal chillers operate at high speed, they have fewer moving parts. Also, they have a broader external structure, which makes them more stable and durable than screw chillers. Carrying out regular maintenance practices like monitoring for vibration and balancing can help improve their stability and lifespan.


● Capacity

There is a big difference in the capacity of screw chillers vs centrifugal chillers, as they cater to varying industrial needs.


Screw chillers have a broader capacity. They can be used for a wide range of applications with varying compression ratios. Their construction supports premium performance across different load conditions, making them the better option for fluctuating air demands.


On the other hand, centrifugal chillers are specifically used for larger industrial applications because of their capacity to handle higher air volumes efficiently.


● Noise and Vibration

Screw Compressor

Noise and vibration levels are crucial factors to consider when examining the operational comfort of screw vs centrifugal compressor.


Screw compressors, because of their compact design and more moving parts, produce greater noise and vibration. Also, the positive displacement mechanism in these compressors add to the generated sound, especially during start-stop operations.


Centrifugal compressors, on the other hand, because of their dynamic and high-speed working mechanism, produce lesser noise and vibration. These compressors have a smoother operation process, resulting in a quieter environment.


● Maintenance and Repair

Maintenance and repair play a crucial role in determining which is better between screw chiller vs centrifugal chiller, and how their overall performance is affected.


Screw chillers, firstly because of their positive displacement mechanism, require more regular maintenance and repairs. Secondly, their working system involves more moving parts, which causes friction that eventually results in wear and tear over time. However, this can be reduced by constant lubrication and inspection practices.


On the other hand, the working system of centrifugal chillers involve fewer moving parts, resulting in less frequent maintenance and repairs.


● Application

Rotary screw vs centrifugal compressor can also be categorized using their applications. Both compressors excel in various industries.


Rotary screw compressors are versatile and perfect for a wide range of applications, which makes them the go-to option for industries with diverse compression needs. They are most-efficient for variable loads and start-stop cycles demands.


Centrifugal compressors are best-suited for larger industrial applications, especially for situations where constant high-speed airflow is needed. Their dynamic operation and scalability make them perfect for tough demanding applications with substantial capacity and efficiency.


Screw vs Centrifugal Compressor in HVAC: Which One is better


Now that we’ve discussed the differences between centrifugal vs screw compressor, it’s time to choose which one is better for your needs.


Overall, screw compressors are best for a wide range of applications, including variable loads and start-stop cycle operations. Centrifugal compressors are the best for larger industrial applications that require dynamic operation with high-speed compression rate.


Also, screw compressors have a simple design and lesser initial costs. But because of their working mechanism that involves many moving parts, they require more maintenance and repairs. This contributes to increased running costs. Additionally, due to the many moving parts, they produce higher noise and vibration.


Centrifugal compressors have a complex design and higher initial costs. But their working mechanism involves fewer moving parts, thereby lesser maintenance and repairs, which lowers running costs. Due to the fewer moving parts, they produce less sound.


SPRSUN is one of the prominent and reliable air to water heat pump manufacturers across the world. We have expertise and knowledge in choosing the best type of compressor for HVAC since compressors directly affect the performance of HVAC systems. We use the best Panasonic compressor to equip Chinese heat pumps. If you are looking for the best professional for personalized advice on compressors for heat pumps or ACs, feel free to contact us.



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