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Compressors – the heartbeat of refrigeration

By Eamonn Ryan

The compressor is commonly described as the ‘engine’ or ‘heart’ of a refrigeration system, with the refrigerant being the blood.

The BITZER Ammonia Compressor Packs (ACPs) for industrial refrigeration. Image supplied by BITZER
The BITZER Ammonia Compressor Packs (ACPs) for industrial refrigeration. Image supplied by BITZER

Compressors are mechanical devices used to increase pressure in a variety of compressible fluids, or gases – and in the case of HVAC&R equipment, to phase shift refrigerants for air conditioning and refrigeration. They come in a number of designs – the main ones being reciprocating, screw, scroll and centrifugal. The right choice depends on the operating environment, load and other design factors.

Hennie Basson, managing member of Coldfact, explains the key the key considerations when it comes to selecting a compressor as being, “the capacity of the compressor, type and range: whether screw, scroll or centrifugal; compressor operating pressures and temperatures; energy efficiency; and also the physical size or dimensions of the compressor”. Daniel de Beer, sub-Saharan Africa regional manager for Copeland, in turn lists the most important factors to consider when selecting a compressor for a specific application as being: efficiency cost, availability, warranty and aftersales support. “A more efficient compressor can help reduce energy consumption and operating costs. It is important to consider the overall cost-effectiveness of the compressor, considering factors such as energy efficiency, maintenance requirements, and expected lifespan.

It is important to choose a compressor that is readily available in the market and supported through a reliable supply chain. It is also wise to consider the length and coverage of the warranty when selecting a compressor, as it can help protect against unexpected repair or replacement costs. Aftersales support must include technical support, maintenance, and repair assistance provided by the manufacturer or authorised service centers. It is important to choose a compressor from a manufacturer that offers reliable aftersales support to ensure prompt resolution of any issues that may arise,” he expands. These factors play a crucial role in selecting a compressor that meets the specific requirements of an application while providing optimal performance, reliability, and cost-effectiveness.

The commercial refrigeration industry has changed drastically in recent years along with changes in customer requirements. Customers today demand an everwidening spectrum of applications, from large centralised systems to small walk-in freezers and coolers. Energy efficiency and environmental sustainability have become business priorities. And digital technologies promise connected, predictable visibility to refrigeration systems. These all affect the compressor market.


The Carrier 19DV centrifugal chillers are the only chillers fitted with a new type of compressor design. Image supplied by AHI-Carrier.
The Carrier 19DV centrifugal chillers are the only chillers fitted with a new type of compressor design. Image supplied by AHI-Carrier.

De Beer says that Copeland has a rich history of innovation and development, having been at the forefront of compressor technology for 102 years. They introduced the first semi-hermetic and hermetic compressors in the 1940s and 1950s, followed by the high-efficiency Discus semi-hermetic, air conditioning, and heating scroll compressors in the 1980s and 1990s. Copeland semi-hermetic compressors were the first to successfully operate with an electric motor inside the compressor casting in 1941. Building upon that success, Copeland advanced the industry with its Copeland Scroll technology launched in 1987.

A scroll compressor is a type of compressor that uses two interleaved spiral-like scrolls to compress refrigerant. It is a hermetic compressor, meaning that it is completely sealed and does not allow any air or pressure to escape. A hermetic scroll compressor is highly compact – as the compressor and motor are placed on a single shaft and sealed together. The coefficient of performance (COP) of a scroll compressor is generally higher than that of a semi-hermetic compressor, says De Beer. This is because scroll compressors have fewer moving parts and are more efficient at compressing refrigerant gas. Additionally, scroll compressors have less leakage and lower friction losses than semi-hermetic compressors, which further improves their efficiency.

“We are seeing a lot more scroll technology adoption within the marketplace, where people see it as a cost effective and efficient solution,” he adds. Copeland manufactures various types of compressors: “We make small hermetic- type compressors similar to that used in a domestic refrigerator, but larger applications as well. We also do semi-hermetic and screw compressor technology, which is where most of the market is positioned. None of that technology is new, having started in the 70s and 80s. “On top of that we developed the scroll technology – and this has been acquiring a share of the refrigeration market for the past 15 years or so to achieve a dominant position as people have transitioned from semi-hermetic to scroll compressors in other markets, while it is now gaining traction in the MEA (Middle East and Africa) region. While its relatively new here, it is by no means a new technology and something that certainly is not new for us,” says De Beer. “The main driver of scroll adoption is the fact that we use this technology in our ZX condensing units. The overall market adoption of our ZX range has put us in a leading position within this segment, where we use scroll technology. This drove adoption as more installers and end-users got familiar with the exceptional reliability of this technology. In addition to this, ongoing innovation has now expanded scroll technology into the hydrocarbon and CO2 market space, with capacity ranges up the 30HP.”

He argues that scroll compressor technology is by far the best in class from a COP perspective – its space and weight requirement takes approximately 30% less space within a unit.” He lists one of its greatest efficiency boosters as being the use of Copeland’s Enhanced Vapor Injection (EVI) with the sub-cooling of the liquid before it gets to the plant, making it a lot more efficient. An intermediate pause on a scroll compressor allows gas bypass from the intermediate compression chamber to the discharge side. This technique helps reduce over- compression loss and maintain high efficiency over a wider compression ratio range. This sub-cooling process uses some energy but increases the capacity of the compressor by 30 to 40%. “From a COP perspective, this is far superior over other technology.”

The BITZER CKHE7 CO2 compressor for large capacity trans-critical applications. Image supplied by BITZER
The BITZER CKHE7 CO2 compressor for large capacity trans-critical applications. Image supplied by BITZER

Modulation technologies in scroll compressors is another technology that De Beer describes as having been around for some years. According to Copeland’s website, it allows systems to run at varying capacities to meet cooling demands. These technologies offer several benefits, including increased temperature control, less dehumidification, higher efficiency, reliability, and comfort. In commercial applications, modulation technologies enable cooling systems to adjust capacity as needed. These technologies include multiplexing, variable speed systems, and modulating compressors with 10-100% modulation capabilities. They provide flexibility in meeting cooling demands while reducing energy consumption.

Digital modulating scroll compressors feature infinite capacity control between 10% and 100%. An internal unloading mechanism opens a bypass port or vent at the end of the first compression pocket, allowing the compressed gas to be vented into the beginning of a suction pocket within the scroll. When the bypass port is opened, the effective displacement of the scroll is reduced to 0%, and when it is closed, the scroll operates at 100% capacity. The adoption of this technology has surpassed that of the use of variable speed drives (VSD). This is mostly driven by the simplicity of the technology, where you only have a coil which is either energised or not. Should one have a coil failure, the compressor maintains 100% capacity.

These modulation technologies have become increasingly important due to government mandates around the world for energy-efficient cooling systems and the phaseout of refrigerants like R-22. They offer improved efficiency and performance for both residential and commercial applications. Compressor installation and maintenance come with some associated safety hazards. De Beer explains that the use of natural refrigerants has increased risks associated with installations and maintenance. “This can easily be mitigated through ongoing training and development programmes, which the industry needs to invest in.” There are seldom failures when it comes to installing Copeland compressors. Where there are, De Beer says: “We find that most issues and failures can be prevented through proper installation and commissioning practices.

Compressors are not made to fail, and a well-installed and properly maintained compressor will outlast most of its applications.” He notes that compressors are becoming increasingly energy-efficient and environmentally friendly: “We drive constant innovation throughout our product range and our compressors technologies are best in class. We utilise our global footprint and our extensive regional distribution network to drive customer support. In addition to this, we constantly invest in training, which we found to be the best tool to support our techno-savvy contractor base in the sub- Saharan Africa region.”


One of the first compressors from Bundesfachsule Kaiti Kilma Technik Museum, Frankfurt, Germany. Image supplied by Hennie Basson.
One of the first compressors from Bundesfachsule Kaiti Kilma Technik Museum, Frankfurt, Germany. Image supplied by Hennie Basson.

De Beer lists newer innovations to the technology as being the use of smart controls in the compressors. “In South Africa, the energy crisis has prompted companies to seek different types of modulating technology as well. Even though variable speed technology exists, it adds complexity to a design by requiring an electrician – and so in South Africa we have shifted more and more towards the use of digital unloading for modulation which is a simpler, mechanical means of reducing load from a compressor as opposed to the use of VSD.” Digital unloading is a method used to control the capacity of a compressor. It is an alternative to using VSDs in certain compressor applications.

VSDs are commonly used in compressors to control the speed of the motor, which in turn controls the capacity of the compressor. By adjusting the motor speed, VSDs can modulate the output of the compressor to match the demand for compressed refrigerant. This allows for energy savings and improved efficiency, as the compressor only operates at the required capacity. Digital unloading, on the other hand, is a method that uses digital control algorithms to adjust the capacity of a compressor without the need for a VSD. It achieves this by controlling the opening and closing of inlet valves or unloading mechanisms in the compressor. By adjusting these mechanisms, digital unloading can effectively modulate the capacity of the compressor to match the demand for compressed gas, with the use of a solenoid only.

The effect of digital unloading is similar to that of VSDs in terms of energy savings and improved efficiency. By adjusting the capacity of the compressor to match the demand, both methods will reduce energy consumption and minimise wasteful operation. However, digital unloading may have some advantages over VSDs in certain applications. For example, digital unloading can be more cost-effective, is simpler to implement compared to VSDs, is less impacted by load shedding challenges and provides better oil management due to the fact that the system operates at full volume flow.


A scroll compressor and a semi- hermetic compressor are two different types of compressors used in various applications. Here are the pros and cons of each:

Scroll compressor:


  • Energy efficiency: Scroll compressors are known for their high energy efficiency, which can lead to reduced energy consumption and lower operating costs.
  • Better ability to handle unwanted liquid returning to the compressor Lower oil carry-over (less than 1.5%) leads to improved system efficiency Lower cost compared to other technologies, making this a favourable alternative in a price-sensitive environment.
  • The design of the Copeland scrolls provides mechanically unloaded starts, which improves efficiency Quiet operation: They operate quietly, making them suitable for noise- sensitive environments.
  • Fewer moving parts: Scroll compressors have fewer moving parts compared to other compressor types, resulting in reduced maintenance requirements and improved reliability.
  • Compact design: They have a compact design, making them suitable for applications with limited space High reliability: Scroll compressors are known for their high reliability and long service life

  • Limited capacity range: Scroll compressors are generally available in smaller capacity ranges compared to other compressor types
  • Non-serviceability: when a compressor fails it is replaced with a new one

Semi-hermetic compressor:


  • Serviceability: Semi-hermetic compressors can be repaired in case of failure, as the casing can be opened without damaging it
  • Durability: They offer more durability than open-type compressors as they are sealed against external contaminants
  • Copeland semi-hermetic compressors are supplied with ‘discuss valves’, which provide optimal compression efficiency.


  • Maintenance: Semi-hermetic compressors require regular maintenance, including oil changes, to ensure optimal performance and longevity
  • Larger size: They have a less compact construction compared to scroll compressors, which may limit their suitability for applications with space constraints
  • Higher cost compared to scroll compressors



A Sabroe screw compressor. Image supplied by Sabroe
A Sabroe screw compressor. Image supplied by Sabroe


Earlier this year ebm-papst announced it was expanding its product portfolio to include turbo compressors for different air and gas mixtures. These turbo compressors are used in heat pumps, self-contained drinking water systems and gas supply systems for fuel cells, for example. All components, from the drive motor to the compressor impeller and the newly developed oil-free high-speed bearings, are coordinated to suit the specific application.

Designed as a platform solution, individual compressors with outputs from 1 to 45 kW can be quickly assembled and different refrigerants, air and other gas mixtures can be compressed without oil. Thanks to their high speeds, the turbo compressors are more compact than conventional solutions, operate vibration-free and do not require any lubricating oil. This is of interest wherever gas purity is required. The gas bearing, which is not subject to contact or friction during operation, not only achieves a long service life but also has impressively low noise levels.

The new compressor platform enables a wide range of different applications to be operated economically. By combining different impeller sizes and blade geometries, it enables optimum aerodynamic adaptation to the application. This means that, depending on requirements, the impellers can be matched to the required mass flow or pressure ratio and the working gases used, such as air or R290. The P1 (1 kW) and P2 (2.8 kW) platforms are already available as prototypes and are also in use in customer applications. Series production processes were already considered in the concept phase, which will contribute to a competitive cost structure in future series production. With the help of the technical centre currently under construction at the main site in Mulfingen, Germany, the first small series will start as early as the beginning of 2024. Series production, which is planned from 2026, is aiming for volumes significantly higher than one hundred thousand units per year and platform size.


According to Danfoss’ website its Turbocor compressor is an oil-free magnetic bearing compressor designed for the HVAC industry. It is known for its high efficiency, low sound levels, and compact footprint. The compressor utilises advanced technology such as oil-free, magnetic bearings that provide world-class efficiency and zero performance degradation over the life of the compressor.

Some of its key features and benefits:

  • Energy efficiency: it is 35% more energy efficient, achieved through its built-in Variable Frequency Drive (VFD) that optimises speed based on varying load Being oil-free, it eliminates the need for an oil management system, preventing performance degradation over time. The friction-free magnetic bearings reduce wear and tear, resulting in improved long service life.
  • The Turbocor compressor can be used in air-cooled, water-cooled, or evaporative-cooled chillers across a wide range of applications such as comfort cooling, low-temperature processes, ice storage, and heat recovery. It is equipped with intelligent features such as voltage fluctuation sensing and self-monitoring capabilities.


Compressors with permanent magnet motors controlled by DC inverters are one of the most efficient technologies available in the world for HVAC/R applications, says CAREL. This technology, originating from Japan, is becoming the market standard in home air-conditioning and heating applications. For almost 10 years, CAREL has been helping to disseminate this technology in both refrigeration and air-conditioning applications, especially the most energy- hungry of these, such as heat pumps, air-conditioners for data centers, water chillers, condensing units and refrigerated showcases.

The results are energy savings of up to 60% thanks to the capacity to adapt to the cooling or heating demand in real time; down to less than 10% of the nominal load, with minimum power consumption and consequent extremely high seasonal energy efficiency ratio when compared to the most diffuse fixed speed compressor units. All of this would not be possible without the Power Plus family of inverters, the only devices available on the market that can control 100+ different models of DC compressors, among scroll, rotary, twin rotary and reciprocating technologies, made by the world’s leading manufacturers, with cooling capacities up to 50kW or 90cc displacement.

These also include various refrigerant applications, such as HCFs (for example, R410A, R404A, R407C, R134a), natural refrigerants (such as CO2, propane) and options, such as liquid injection, vapour injection, vertical or horizontal layout. Being combined with the pCO and c.pCO series controllers, and Electronic Expansion Valves of the ExV family, this ‘CAREL system’ integrates the compressor’s electrical and thermodynamic characteristics, and is engineered based on in-depth lab tests conducted in collaboration with the compressor manufacturers.

Maximum efficiency and total reliability are therefore guaranteed by dynamic control of the compressor envelope, the area in which correct operation is guaranteed. However, when dealing with thermodynamics, the compressor envelope control is just the tip of the iceberg. Dedicated functions have been developed to manage any compressor operating variable, such as discharge and sump temperatures, oil circulation, suction and discharge superheat as well as speed ramps and start-up and stop procedures. CAREL’s experience in this sector has also allowed this system to be upgraded with exclusive functions to protect the compressor and optimise the entire refrigeration system.

These are the reasons why the Power Plus is actually a compressor drive, rather than just a ‘general purpose’ inverter, as the motor speed control is just a small portion of all its numerous functions dedicated to the compressor management. In the end, this CAREL control system is integrated into the final HVAC&R application, for example a heat pump, a condensing unit or a showcase so as to ensure the technology meets all the needs of the OEM and of the end user.

A Recip Compressor. Image supplied by Sabroe
A Recip Compressor. Image supplied by Sabroe

Some examples?

  • When driving water chillers, the Carel DC compressor system is able to directly control the water outlet temperature, reducing or even zeroing the need of a water tank buffer and allowing a more strict humidity control on the hydronic terminals.
  • When driving a refrigerated plug- in display case, its precise capacity modulation allows one to reduce the number of defrosts per day with a consequent reduction of the energy cost of this application and makes the food temperature a ‘straight line’ without any oscillating behaviour increasing the products life.
  • When driving a computer room air conditioning system, its capability to modulate compressor, expansion valve and fans allows the unit to run out of the design working conditions for hours (for example, at unexpected external ambient temperatures) without compromising any component and without interrupting the essential cooling duty.


  3. management
  4. Danfoss website
  5. Emb-papst website