By Tamika Brooks · Updated October 9, 2026 · 8 min read
Short answer
Chillers are classified by how they compress refrigerant (scroll, screw, reciprocating, centrifugal) or use heat instead of a compressor (absorption), and by how they reject heat (air-cooled or water-cooled). Scroll suits small loads, screw the middle range, and centrifugal the largest plants. The best type depends on load size, efficiency goals, ambient conditions, water availability and maintenance capacity.
Chillers fall into two big families. Vapor-compression chillers use a compressor, and they are named for the compressor type: scroll, screw, reciprocating or centrifugal. Absorption chillers use a heat source and a salt solution instead of a compressor. Every chiller is then further described as air-cooled or water-cooled, depending on how it rejects heat. Matching the type to the load, the climate and the people who will maintain it is the main selection decision.
If you need a refresher on the basic cycle first, read how a chiller works. This article compares the types.
What are the main types of chillers by compressor?
Scroll chillers
Scroll chillers use one or more scroll compressors, usually several in parallel on one or two refrigerant circuits. They are quiet, compact and simple. Capacities typically run from a few tons to a couple of hundred tons for packaged units, with staging providing part-load control. Most are air-cooled. Details on the compressor itself are in how a scroll compressor works.
Reciprocating chillers
Piston compressors in cylinders, similar in principle to an engine. They have a long history and are still found in older plants and in some smaller or specialized units. They offer step unloading by deactivating cylinders and field-serviceable parts, but vibration, valve wear and higher maintenance have pushed most new designs toward scroll and screw.
Screw chillers
Screw compressors compress gas between two meshing helical rotors. They are the common choice from roughly the mid-double-digit tons to several hundred tons. A slide valve or a variable speed drive provides smooth capacity control, which helps at part load. Both air-cooled and water-cooled versions are common. See how a screw compressor works and screw vs scroll compressors.
Centrifugal chillers
A high-speed impeller adds velocity to the refrigerant, which is then converted to pressure. Centrifugal machines serve the largest loads, typically from a few hundred tons to several thousand, and are usually water-cooled. Modern units often use magnetic-bearing, oil-free compressors with variable speed drives for strong part-load efficiency. More in centrifugal chillers explained.
Absorption chillers
Absorption chillers produce cooling from heat, such as steam, hot water or direct-fired gas, using a refrigerant and absorbent pair, most commonly water and lithium bromide. They have few moving parts and use little electricity, but their efficiency (COP) is much lower than that of electric chillers, commonly around 0.7 for single-effect and roughly 1.0 to 1.4 for double-effect designs, and they reject more heat. They make sense mainly where there is cheap or waste heat, as in some cogeneration and district energy plants.
How do air-cooled and water-cooled chillers differ?
The heat-rejection method is independent of the compressor type, although some combinations are more common than others.
- Air-cooled: Fans move outdoor air through condenser coils. No cooling tower, condenser water pumps or water treatment. Installed outdoors, often on a roof or a pad. Capacity and efficiency drop as outdoor temperature rises.
- Water-cooled: Condenser water goes to a cooling tower or a dry cooler. More efficient, especially at larger sizes, but it requires water, treatment and more equipment to maintain.
- Remote condenser: The chiller sits indoors, and the condenser is outdoors. This keeps noise and heat outside but adds refrigerant piping.
A full comparison is in air-cooled vs water-cooled chillers.
How do the chiller types compare?
The ranges below are general industry rules of thumb. Individual manufacturers and models vary, so use them for orientation, not for specifications.
| Type | Typical capacity range | Usual heat rejection | Strengths | Trade-offs |
|---|---|---|---|---|
| Scroll | A few tons up to about 200 tons | Mostly air-cooled | Compact, quiet, simple, low first cost | Many compressors in large units, more circuits to service |
| Reciprocating | Small to mid-size | Air or water | Serviceable parts, familiar technology | Vibration, valve wear, higher upkeep, less common in new designs |
| Screw | About 50 to 500+ tons | Air or water | Good part load with slide valve or VFD, robust | Oil system, more costly than scroll at small sizes |
| Centrifugal | About 150 to 6,000+ tons | Mostly water-cooled | Highest efficiency at large sizes, fewer wear parts | Higher first cost, needs minimum load, tower and water systems |
| Absorption | A few tons to over a thousand | Water-cooled | Uses heat instead of electricity, quiet | Low COP, bigger footprint, specialized upkeep |
Which type fits which application?
Use these as starting points, not rules:
- Small commercial building or light process load: air-cooled scroll.
- Mid-size campus, hospital wing, or industrial process: air-cooled or water-cooled screw, often two machines for redundancy.
- Large central plant or data center: water-cooled centrifugal or screw with variable speed drives. For data-center context see data center cooling explained.
- Facilities with free or waste heat: absorption, alone or combined with electric chillers.
- Process cooling below about 40°F or with antifreeze: a glycol-capable design. See glycol chillers explained.
- Large food, cold-storage or industrial refrigeration: ammonia systems, covered in ammonia refrigeration system basics, although these are usually described as refrigeration plants rather than packaged chillers.
What else should you consider besides type?
- Load profile. Constant loads favor different machines than highly variable loads. Part-load efficiency matters more than full-load for most buildings. See chiller efficiency: kW per ton and IPLV.
- Sizing and redundancy. Two smaller machines can be better than one large one. Read chiller sizing basics.
- Climate. Hot summers reduce air-cooled capacity. Water-cooled machines depend on wet-bulb conditions instead.
- Refrigerant. Regulations are moving the market toward lower-GWP refrigerants. See what is changing in 2026.
- Water and space. Water-cooled plants need makeup water, treatment and mechanical room space.
- Maintenance capability. Who will service it, and are parts available locally?
- Noise and code. Check local noise limits and the latest mechanical code changes.
Frequently asked questions
Which type of chiller is the most efficient?
At full and part load, large water-cooled centrifugal chillers with variable speed drives are generally the most efficient electric machines, with full-load figures commonly in the range of about 0.5 to 0.6 kW per ton or lower. Air-cooled chillers are less efficient, commonly around 0.9 to 1.3 kW per ton. Actual values depend on conditions and model, so compare certified ratings.
What is the difference between a chiller and an air conditioner?
An air conditioner or rooftop unit cools air directly with a refrigerant coil. A chiller cools water or a glycol mix, which is then piped to coils elsewhere. Chillers suit large buildings and process loads with many cooling points. See CRAC vs CRAH vs chiller for a related comparison.
Are absorption chillers still used?
Yes, though in a narrow set of cases. They are most competitive where waste heat, steam or low-cost natural gas is available, and where electricity capacity is limited. In ordinary commercial buildings, electric chillers generally dominate.
SpecServis engineers in Ukraine work with industrial chillers and refrigeration plants. We are planning to enter the Central Texas market and are looking for technicians, partners and a company to buy. See our open positions or partnership options.
