By Tamika Brooks · Updated August 12, 2026 · 6 min read
Short answer
A centrifugal chiller compresses refrigerant with a high-speed impeller instead of pistons or screws. It is efficient and compact at large capacity, from about 100 tons to several thousand, and suits hospitals, campuses and data centers. Variable-speed drives and magnetic bearings improve part-load efficiency, while surge at low load and refrigerant choice are the main design limits.
A centrifugal chiller is a water chiller whose compressor is a spinning impeller. The impeller accelerates refrigerant vapor outward, and a diffuser turns that speed into pressure. These machines dominate large cooling plants because they deliver very high capacity from one compressor with relatively few moving parts. The rest of the system, evaporator, condenser and expansion device, is the same as in any chiller; see how a chiller works.
How does a centrifugal compressor work?
The compressor is a dynamic machine, unlike the positive-displacement types in our guide to refrigeration compressor types. Refrigerant gas enters the eye of the impeller, which spins at high speed, thousands of revolutions per minute. The gas leaves at the rim with high velocity, then slows in the diffuser and volute, and that conversion raises pressure. Large machines use two or three impeller stages; small ones use one.
Capacity control has historically used inlet guide vanes (IGV) that throttle the gas entering the impeller. Modern machines combine IGVs with variable-speed drives (VFD), which slow the motor as load drops and saves considerable energy at part load.
What capacity range do centrifugal chillers cover?
Ranges depend on manufacturer and line, but published product data gives a sense of scale:
| Example line (manufacturer data) | Approximate range |
|---|---|
| Carrier AquaEdge 19PV, magnetic bearing | about 100 to 350 tons |
| YORK YZ, magnetic bearing | about 165 to 2,000 tons |
| Daikin Magnitude, magnetic bearing | about 86 to 1,600 tons, with larger models |
| Large conventional units | up to several thousand tons |
Below roughly 100 tons, screw and scroll chillers are usually the more economical choice. Above a few hundred tons, centrifugal machines become the default. Always use the current manufacturer data for a specific model.
What is surge, and why does it matter?
Surge is an unstable condition in dynamic compressors. When load drops and the compressor must raise pressure with too little flow, gas can reverse direction through the impeller, causing pulsation, noise, vibration and eventual damage. It can also happen when condensing pressure is too high for the machine’s current speed or guide-vane position.
Designers manage surge with:
- Control logic that keeps the compressor away from its surge line.
- Hot-gas bypass at very low loads, which keeps flow up at the cost of efficiency.
- VFDs and IGVs that move the operating point away from surge as conditions change.
- Condenser water control that avoids very high lift at low load.
The practical result is a minimum load below which the chiller cycles off instead of unloading further. Plants with low or widely varying loads often add a smaller chiller or a thermal storage tank so the large machine runs where it is stable.
What are magnetic bearing and oil-free chillers?
Conventional centrifugal compressors use oil-lubricated bearings. Magnetic bearing compressors levitate the shaft with electromagnets, so there is no oil in the refrigerant circuit. Benefits manufacturers cite include:
- No oil system to maintain, and no oil fouling of heat exchangers.
- Very low friction and good part-load efficiency, especially with a built-in VFD.
- Soft starting and low vibration.
Trade-offs include higher first cost for some models, the need for clean, stable power and a controller that manages the bearings, and specialized service skills. Several manufacturers offer them from roughly 100 tons upward, and some now offer very large models.
What refrigerants do centrifugal chillers use?
Common choices include R-134a, R-513A, R-1234ze(E) and R-1233zd(E). The last two are HFOs with very low global warming potential. Some are low-pressure refrigerants, and low-pressure machines may operate with part of the circuit below atmospheric pressure, which affects leak behavior and purge design. Rules are changing: the AIM Act and EPA’s Technology Transitions rule drive the move to lower-GWP options, and EPA revised parts of the rule in 2026. See A2L refrigerants explained for the safety class that many of these newer fluids fall into, and check EPA’s current pages for dates that apply to chillers.
When is a centrifugal chiller the right choice?
- Large, steady loads, such as hospitals, campuses, airports and data centers.
- High efficiency priority, where energy cost dominates over a 20-year life.
- Water-cooled plants with cooling towers, since centrifugals are usually water-cooled; see air-cooled vs water-cooled chillers.
- Space limits, because they are compact for their capacity.
They are a poorer fit for small or highly variable loads, for sites without water, or where a single large machine means no redundancy. In critical facilities, designers use multiple machines in N+1 arrangements.
What are common issues with centrifugal chillers?
- Tube fouling in condenser and evaporator, which raises approach temperature and power use.
- Non-condensables and leaks in low-pressure machines.
- Surge events from poor condenser water control or unstable loads.
- Bearing and oil problems on conventional machines.
- Control and VFD faults.
Logging approach temperatures, amps and pressures is the best defense; the same habit works for compressors, as in five signs a compressor is wearing out.
Frequently asked questions
Are centrifugal chillers more efficient than screw chillers?
At large capacity and with variable speed, usually yes. At small capacity or low loads, screw chillers can be as efficient or better. Compare at your real load profile using IPLV or NPLV and manufacturer data.
How long does a centrifugal chiller last?
With good maintenance they commonly run 20 to 30 years or more. Many plants refurbish or retrofit rather than replace.
Do oil-free chillers need less maintenance?
They remove oil service, but still need tube cleaning, controls checks and water treatment. Specialized training is needed for magnetic bearing systems.
If you work on large chiller plants in Central Texas, we would like to meet you. See our open positions or partnership options.
