Chillers Types, Best Uses, and the Pros and Cons of Each
A chiller is a machine used to produce chilled water for air conditioning or process cooling in large facilities. Most chillers operate using vapor compression, and there are four basic types: reciprocating, centrifugal, screw, and scroll.
Reciprocating chillers draw refrigerant into a compressor through an intake valve, and an internal piston compresses the refrigerant. Pressure forces it through an exhaust valve where it is released back into the system to absorb more heat. Reciprocating chillers can accommodate cooling loads between 30 and 150 tons, and multiple units can be used, allowing flexibility. Reciprocating chillers are the most affordable of all the types, but they require a higher level of maintenance, produce more noise and vibration, and can consume more energy in multiple-chiller configurations.
Screw chillers employ helical rotors to compress the refrigerant, which is forced into spaces created by meshing helical screws within a cylinder. There, it travels the length of the rotors and exits when it reaches the other end. Screw chillers are mid-range units with capacities generally ranging from 20 to 1,000 tons. They have a high compression ratio and few moving parts, which makes them smaller than reciprocating and centrifugal chillers of similar capacity. They are quiet, vibration-free, reliable, efficient, and require very little maintenance. The main drawback is higher initial costs.
Centrifugal chillers use an impeller wheel to force refrigerant against the sides of a cylindrical chamber, then exhaust the compressed refrigerant to continue the cycle. Centrifugal chillers can handle large volumes of refrigerant, and because their compressive force is relatively small, multiple impellers are often used. They have the largest capacity – up to 2,000 tons – and are often used in applications requiring 300 tons and larger, and are the least costly and most efficient design when operating at full load. When used for lower loads, chiller surge can often be a problem.
Scroll chillers have the smallest capacity of the four types, commonly ranging from 5 to 150 tons. Two offset spiral disks are nested together, one stationary and one rotating. Refrigerant is compressed into the center of the spiral where it is exhausted back into the system. Scroll chillers are compact, efficient, quiet, and low-maintenance. They're often used in smaller applications and can be good options for spot cooling and make-up cooling.
There are many option packages and accessories available that can increase chiller efficiency, control, and user-friendliness. For more information on what type of chiller best meets your needs, please contact PJM Mechanical Contractors, Inc. at (609) 496-8696.