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Centrifugal vs screw chiller: which to spec for your plant
Centrifugal leads on large-tonnage efficiency; screw wins on part-load toughness, high lift, and air-cooled flexibility.
Short answer
Pick a water-cooled centrifugal when the plant is large and efficiency is the goal; pick a screw for the mid range or where the load is rough, the lift is high, or surge-free operation matters more than the last bit of full-load efficiency. The single biggest deciding factor is tonnage against load profile: above roughly 500 to 1,000 tons the centrifugal takes over and stays the efficiency leader, while the screw holds the mid-to-large range and covers jobs a centrifugal would oversize. Both are rated to AHRI 550/590, so compare certified IPLV or NPLV at your design conditions, not the headline number.
Centrifugal chiller vs Screw chiller: side by side
| Factor | Centrifugal chiller | Screw chiller |
|---|---|---|
| Compressor mechanism | Dynamic; spinning impeller adds velocity, diffuser converts to pressure | Positive displacement; twin meshing helical rotors trap and squeeze gas |
| Typical capacity | Roughly 150 to 3,000 tons, more in multi-compressor sets | Roughly 70 to 1,500-plus tons |
| Full-load efficiency | Best at scale; water-cooled leads all types, gap widens with tonnage | Strong but below centrifugal at large tonnage |
| Heat rejection | Almost always water-cooled | Air-cooled or water-cooled, which is why it shows up everywhere |
| Part-load / low-load behavior | Can surge at low load or high lift; managed with guide vanes and VFD | Does not surge; holds capacity and pressure across a wide load range |
| Maintenance driver | Oil system on geared machines, or none on magnetic-bearing; watch tubes | Oil-flooded; routine oil analysis, oil and filter changes, bearing watch |
| Best use | Large chilled-water plants: high-rises, hospitals, campuses, data centers | Mid-size buildings, packaged air-cooled jobs, rough or high-lift loads |
| Rating standard | AHRI 550/590 certified kW per ton and IPLV/NPLV | AHRI 550/590 certified kW per ton and IPLV/NPLV |
Which should you pick?
Choose Centrifugal chiller when
- Tonnage is large, roughly 500 to 1,000 tons and up, where the centrifugal is the efficiency leader
- A cooling tower is acceptable and the spec chases the lowest kW per ton and IPLV
- The plant runs long hours at part load and a variable-speed or magnetic-bearing machine can pay back its first cost
- The load is steady, like a data center running every hour of the year
Choose Screw chiller when
- Load sits in the mid-tonnage range where a centrifugal is oversized
- You want an air-cooled packaged outdoor chiller and no cooling tower
- The lift is high or the load profile is rough and surge-free operation matters
- Redundancy through multiple staged machines beats one large unit for the building
Bottom line
It depends on tonnage and load profile. At large capacity with a tower and a long part-load life, the water-cooled centrifugal, especially variable-speed or magnetic-bearing, is the efficiency answer and anchors most big plants. In the mid range, on tight or towerless sites, or where the lift is high and the load swings hard, the screw's surge-free operation and air-or-water flexibility make it the safer workhorse. Size to a real peak load, then confirm the model in the manufacturer's selection software and compare candidates on certified IPLV or NPLV at your own water temperatures, not on full-load numbers or first cost alone.
FAQ
When should I choose a screw chiller over a centrifugal?
Choose a screw in the mid-tonnage range where a centrifugal is oversized, or where the load is rough, the lift is high, or surge-free operation matters. Screws are positive-displacement, so they do not surge and hold capacity well at part load. They also come air-cooled or water-cooled, which centrifugals rarely do.
Which is more efficient, centrifugal or screw?
At large tonnage the water-cooled centrifugal is more efficient and the gap widens as tonnage grows; variable-speed and magnetic-bearing centrifugals can reach into the low 0.3s kW per ton on IPLV. The water-cooled screw ranks just behind it. Verify the AHRI 550/590 certified rating at your design conditions, because lift and water temperatures move the result.
Do screw chillers surge like centrifugals?
No. Surge is a centrifugal failure mode: at low load or high lift the impeller cannot hold pressure and flow reverses, which is heard as a rumble and is hard on bearings. A screw is positive-displacement, trapping and squeezing a pocket of gas, so it does not surge and tolerates a wide load range, which is a main reason it is picked where the load is rough.