By Yevhen Kovalchuk · Updated September 24, 2026 · 6 min read
Short answer
Refrigeration compressors are positive-displacement (reciprocating, scroll, screw) or dynamic (centrifugal). Scroll fits small to mid capacity, reciprocating covers a wide range, screw dominates mid to large industrial duty and centrifugal serves very large chillers. Each can be hermetic, semi-hermetic or open drive, which decides serviceability and refrigerant compatibility.
A refrigeration compressor draws in low-pressure refrigerant gas and compresses it so the system can reject heat. Compressors fall into two families: positive displacement (reciprocating, scroll, screw), which trap and squeeze a fixed volume of gas, and dynamic (centrifugal), which add energy with a spinning impeller. The right type depends on capacity, refrigerant, efficiency needs and who will service it.
What are the main compressor types?
| Type | How it compresses | Typical capacity | Typical use |
|---|---|---|---|
| Reciprocating | Pistons in cylinders | very small to large | Commercial refrigeration, racks, ammonia plants, older chillers |
| Scroll | Two spiral scrolls, one orbiting | small to about 60 tons per unit in tandem | Light commercial, chillers, heat pumps |
| Screw | Two meshing helical rotors | mid to very large | Industrial refrigeration, process chillers |
| Centrifugal | Impeller adds velocity, converted to pressure | large, hundreds to thousands of tons | Large chillers |
Ranges vary by manufacturer and refrigerant. Use them as a starting point, not a selection tool.
Reciprocating compressors
They use pistons and valves like a small engine. They are robust and cover a wide range, with good efficiency at moderate pressure ratios. Drawbacks include more moving parts, valve wear and vibration. Many commercial refrigeration compressors, including semi-hermetic ones, are reciprocating.
Scroll compressors
Two spiral elements compress gas continuously with few moving parts. They are quiet and efficient in their range, and common in rooftop units and small chillers. They are usually hermetic and are replaced rather than rebuilt in the field. Larger capacity comes from tandem or multiple compressors.
Screw compressors
Two helical rotors mesh, trapping gas and squeezing it along the length of the rotors. Oil injection seals and cools. Screws handle high capacities and high pressure ratios, and capacity control uses a slide valve or variable speed. They are the workhorse of industrial refrigeration. See how a screw compressor works.
Centrifugal compressors
An impeller spins at high speed and converts velocity to pressure. They are efficient at large capacities and suit big water chillers. They need minimum flow to avoid surge and are less common below a few hundred tons.
What are hermetic, semi-hermetic and open compressors?
This is about the housing, not the compression method:
- Hermetic. Motor and compressor sealed in a welded shell. Compact and leak-tight, but not field-serviceable. Common in small scroll and rotary units.
- Semi-hermetic. Bolted housing with the motor inside the refrigerant circuit. Service access allows overhaul. Used in commercial and mid-size equipment.
- Open drive. The motor is outside, connected by a shaft with a mechanical seal. Required for ammonia, since ammonia attacks copper windings, and allows any motor type.
Selection affects serviceability, leak points and refrigerant compatibility.
How do you choose a compressor type?
- Capacity and range. Match to the load and how widely it varies.
- Refrigerant. Ammonia needs open-drive designs without copper wetted parts; HFCs and HFOs suit hermetic and semi-hermetic designs.
- Efficiency at part load. Screws and variable-speed units handle varying loads well; scrolls and reciprocating use staging.
- Serviceability. Open and semi-hermetic compressors can be overhauled; hermetic units usually cannot.
- Noise, vibration and space. Scroll is quiet; reciprocating needs vibration control.
- Future refrigerant. Check that the design is approved for lower-GWP refrigerants; see A2L refrigerants explained.
What questions help narrow the compressor type?
Rather than starting with a brand, answer a few questions about the duty.
- What is the capacity range? Small loads favor scroll or hermetic reciprocating; large industrial loads favor screw or centrifugal.
- How much does the load vary? Wide swings favor capacity control such as slide valves or variable speed; see variable-speed VFD compressors.
- What is the evaporating temperature? Low-temperature duty narrows the options and changes oil and refrigerant choices.
- How serviceable should it be? Sealed units are replaced, while semi-hermetic and open units can be rebuilt. See rebuild vs. replace.
- Which refrigerant? Check approval and oil compatibility with compressor oil types.
For a side-by-side look at two common choices, read screw vs. scroll compressors. Writing the answers down turns a vague preference into a short specification you can hand to a supplier.
Frequently asked questions
Which refrigeration compressor is most efficient?
It depends on the capacity and operating conditions. Centrifugal and screw compressors are efficient at large capacities; scrolls are efficient in their range. Compare using manufacturer data at your conditions.
What is the difference between a compressor and a condensing unit?
A condensing unit packages a compressor, condenser coil, fans and controls into one outdoor assembly.
How do you identify a compressor?
Read the nameplate; see how to read a compressor nameplate.
SpecServis has worked with screw and reciprocating compressors in Ukraine. We are planning to enter the Central Texas market and are looking for people and partners. See our open positions or partnership options.
