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4 Types of HVAC Compressors

Industrial compressor at a refrigeration station - 4 types of HVAC compressors

Four types of HVAC compressors were born out of a necessity to solve specific issues related to different types of HVAC units. Noise levels, space constraints, energy efficiency, unit capacity, maintenance accessibility and, of course, cost are all factors special to the size, scale and capacity of the HVAC unit in question.

Although each compressor design addresses the problems listed above, they essentially do the same thing: compress the refrigerant to facilitate efficient heating and cooling of an enclosed space. In this guide, we’ll explain how compressors work and their applications.

What Does an HVAC Compressor Do?

In a nutshell, the role of a compressor within an HVAC system is to move the refrigerant between the evaporator, condenser and expansion valve in an enclosed loop. The condenser takes low-pressure refrigerant vapor and compresses it into high-pressure refrigerant vapor by decreasing its volume. This, in turn, increases its pressure and temperature so it can then travel through the discharge line to the condenser, where it dissipates its heat and turns it back into its liquid form, enabling the cooling process.

Types of HVAC Compressors

There are four primary types of compressors for HVAC systems: Reciprocating (piston) compressors, screw (rotary or helirotor) compressors, scroll compressors and centrifugal compressors. We’ll take a more detailed look at what sets them apart below.

1. Reciprocating Compressor 

Reciprocating compressors are a kind of positive displacement compressor and are the most common type of compressors used in HVAC, as they are highly efficient and versatile cooling components. Reciprocating compressors use piston technology to pull refrigerant from the suction line into its chamber. 

As the piston moves upward, it compresses the refrigerant into high-pressure vapor. The piston pushes it out through the discharge line, where the condenser turns the refrigerant back into its liquid state, beginning the cycle anew.

2. Screw Compressor 

Screw compressors are typically seen in larger HVAC units because they are more efficient and better suited for industrial and commercial settings. They consist of two interlocking screws, known as rotors, that turn to transport and compress the refrigerant from low-pressure refrigerant vapor to high-pressure refrigerant vapor. 

As the screws rotate, the refrigerant gas gets trapped between the walls of the screw and the chamber. Meanwhile, due to the shape of the screw, the volume of space decreases, increasing the pressure and temperature of the refrigerant. Unlike piston compressors that work in perfectly timed bursts, screw compressors can compress refrigerants continuously, making them more efficient.

3. Centrifugal Compressor 

Centrifugal compressors are a type of dynamic compressor used in large-scale HVAC units for industrial and commercial applications. Different from positive displacement compressors, these types of HVAC compressors use an impeller with radial blades, a diffuser and a high-speed motor to achieve the same ends. 

Refrigerant gas goes in through the impeller at high velocities. As the impeller spins, the gas velocity increases as it gravitates further from the rotational axis. This is important because the diffuser's job is to reduce the velocity of the gas. At this point, you might be wondering why you would go to such lengths to increase the velocity only to slow it down again. Dramatically increasing and rapidly decreasing its velocity converts the refrigerant’s kinetic energy to potential energy, ie. pressure.

Scroll Compressor 

Scroll compressors are the newest of all the different types of HVAC compressors but are swiftly becoming more common due to their higher energy-efficient designs, quieter operations and increased durability. It is also a type of positive displacement compressor. As its namesake suggests, scroll compressors utilize two interconnected spiral-shaped scrolls to compress refrigerant into its high-pressure gaseous state.

Where one coil is fixed, the other one orbits. As it orbits, it draws in low-pressure refrigerant gas from the suction line, guiding it around the coil. The small, circular motions decrease the volume of the gas pockets, increasing the pressure until it's expelled through the discharge line. In this regard, they’re very similar to screw compressors since they can continuously compress refrigerant without interruption.